Journeyman Electrician (NEC) — All Questions

A 208-volt, single-phase branch circuit supplies a continuous load of 24 amperes. What is the minimum standard overcurrent device rating permitted?

• a.30 amperes✓
• b.25 amperes
• c.24 amperes
• d.40 amperes

An overcurrent device supplying a continuous load must be rated at not less than 125 percent of that load: 24 A x 1.25 = 30 A, which is a standard rating in 240.6(A). The 24 A and 25 A choices ignore or under-apply the 125 percent factor, and 40 A jumps past the next standard size above the calculated value.2023 NEC §210.20(A)

For that same 24-ampere continuous load, what is the minimum size copper branch-circuit conductor, assuming 75 degrees C terminations and THWN insulation?

• a.12 AWG
• b.10 AWG✓
• c.8 AWG
• d.14 AWG

The conductor must carry at least 125 percent of the continuous load, or 30 A. In the 75 degrees C column of Table 310.16, 12 AWG copper is only 25 A, so it fails; 10 AWG copper is 35 A and is adequate, and 240.4(D) still allows a 30 A device on 10 AWG. Choosing 8 AWG is oversized for the minimum asked, and 14 AWG is limited to 15 A.2023 NEC §210.19(A)

Six current-carrying 12 AWG THHN copper conductors are installed in a single EMT run at a 30 degrees C ambient. What is the adjusted ampacity of each conductor before termination limits are applied?

• a.25 amperes
• b.20 amperes
• c.22.5 amperes
• d.24 amperes✓

Start in the 90 degrees C column of Table 310.16, where 12 AWG THHN is 30 A, then apply the adjustment factor for 4 through 6 current-carrying conductors, which is 80 percent: 30 A x 0.80 = 24 A. The 22.5 A answer wrongly starts from the 75 degrees C value of 25 A, 25 A applies no adjustment at all, and 20 A is simply the 60 degrees C table value.2023 NEC §310.15(C)(1)

Four current-carrying 8 AWG THWN-2 copper conductors run in a raceway through a 48 degrees C ambient. What is the adjusted ampacity of each conductor?

• a.36 amperes✓
• b.44 amperes
• c.40 amperes
• d.33 amperes

Begin with the 90 degrees C ampacity of 8 AWG copper, 55 A, then correct for the 46 to 50 degrees C ambient range at 0.82 and adjust for four current-carrying conductors at 0.80: 55 x 0.82 x 0.80 = 36 A. Answers of 40 A and 44 A apply only one of the two required factors, and 33 A comes from starting in the 75 degrees C column, which is not required when a 90 degrees C conductor is used as the derating base.2023 NEC §310.15

A 120-volt circuit carries 20 amperes through 12 AWG copper (6,530 circular mils) to a load 100 feet away. Using K = 12.9, what is the approximate voltage drop?

• a.10.5 volts
• b.3.9 volts
• c.5.2 volts
• d.7.9 volts✓

For a single-phase circuit, VD = (2 x K x I x L) / CM = (2 x 12.9 x 20 x 100) / 6,530 = 51,600 / 6,530, or about 7.9 volts. The 3.9-volt answer forgets that current travels out and back, so it omits the factor of 2; 5.2 volts and 10.5 volts do not correspond to any correct combination of the formula terms.2023 NEC Chapter 9, Table 8

A 480-volt, three-phase feeder carries 40 amperes 250 feet using 6 AWG copper (26,240 circular mils). Using K = 12.9, what is the approximate voltage drop?

• a.14.8 volts
• b.4.9 volts
• c.8.5 volts✓
• d.17.0 volts

For three-phase, VD = (1.732 x K x I x L) / CM = (1.732 x 12.9 x 40 x 250) / 26,240, or about 8.5 volts, roughly 1.8 percent of 480 volts. The 17.0-volt answer uses the single-phase factor of 2 instead of 1.732, 4.9 volts halves the run length, and 14.8 volts does not follow from the given values.2023 NEC Chapter 9, Table 8

A 120-volt branch circuit must carry 12 amperes 120 feet with voltage drop held to 3 percent. Using K = 12.9 for copper, what is the smallest conductor that meets the target?

• a.8 AWG
• b.14 AWG
• c.12 AWG
• d.10 AWG✓

Three percent of 120 volts is 3.6 volts, so the required area is CM = (2 x 12.9 x 12 x 120) / 3.6 = 37,152 / 3.6 = 10,320 circular mils. From Chapter 9, Table 8, 12 AWG has only 6,530 circular mils and fails, while 10 AWG has 10,380 circular mils and just satisfies the requirement. 8 AWG works electrically but is larger than the minimum asked for, and 14 AWG is far too small.

A feeder supplies 30 amperes of continuous load plus 50 amperes of noncontinuous load. What is the minimum standard overcurrent device rating?

• a.100 amperes
• b.80 amperes
• c.90 amperes✓
• d.110 amperes

The device must be sized for the noncontinuous load plus 125 percent of the continuous load: 50 + (30 x 1.25) = 87.5 A, and the next standard size in 240.6(A) is 90 A. The 80 A answer simply adds the loads without the 125 percent factor, and 100 A or 110 A skip past the next standard rating.2023 NEC §215.3

Which of the following is NOT a standard ampere rating for fuses and inverse-time circuit breakers?

• a.110 amperes
• b.45 amperes
• c.70 amperes
• d.55 amperes✓

The standard ratings listed in 240.6(A) include 45, 50, 60, 70, 80, 90, 100 and 110 amperes, but 55 amperes is not among them. Knowing this list matters because calculated loads are routinely rounded up to the next standard rating, and selecting a size that does not exist is a common exam trap.2023 NEC §240.6(A)

What is the minimum number of 20-ampere small-appliance branch circuits required for the kitchen, pantry, breakfast room and dining room receptacles of a dwelling unit?

• a.One
• b.Two✓
• c.Three
• d.Four

At least two 20-ampere small-appliance branch circuits must serve the receptacle outlets in those rooms, and those circuits may not supply other outlets. One circuit is below the minimum, while three or four exceed the code minimum and are design choices rather than requirements.2023 NEC §210.11(C)(1)

What is the minimum branch-circuit rating for the receptacle outlets serving a dwelling unit bathroom?

• a.15 amperes
• b.20 amperes✓
• c.25 amperes
• d.30 amperes

A dedicated 20-ampere branch circuit is required for bathroom receptacle outlets, and it may serve only bathroom receptacles unless it supplies a single bathroom entirely. A 15-ampere circuit is not permitted for this purpose, and 25 or 30 amperes are not used for 125-volt, 15- and 20-ampere receptacle circuits.2023 NEC §210.11(C)(3)

What is the allowable ampacity of 8 AWG copper Type NM cable?

• a.40 amperes✓
• b.55 amperes
• c.50 amperes
• d.45 amperes

The ampacity of Type NM cable must be taken from the 60 degrees C column of Table 310.16, where 8 AWG copper is 40 A, even though the conductors inside carry a 90 degrees C rating. The 50 A and 55 A choices come from the 75 degrees C and 90 degrees C columns, which may be used only as a starting point for derating, not as the final NM cable ampacity.2023 NEC §334.80

A feeder supplies a 100-ampere continuous load. Using 75 degrees C terminations and copper THWN, what is the minimum feeder conductor size?

• a.1 AWG✓
• b.2 AWG
• c.1/0 AWG
• d.3 AWG

The feeder conductor must have an ampacity of at least 100 x 1.25 = 125 A. In the 75 degrees C column, 2 AWG copper is 115 A and falls short, while 1 AWG copper is 130 A and satisfies the requirement. 1/0 AWG at 150 A is larger than necessary, and 3 AWG at 100 A does not cover the continuous-load multiplier.2023 NEC §215.2(A)(1)

Nine current-carrying 10 AWG THHN copper conductors share one raceway at a 30 degrees C ambient. What is the adjusted ampacity of each?

• a.35 amperes
• b.24.5 amperes
• c.26.3 amperes
• d.28 amperes✓

The 90 degrees C ampacity of 10 AWG copper is 40 A, and the adjustment factor for 7 through 9 current-carrying conductors is 70 percent: 40 x 0.70 = 28 A. The 26.3 A answer applies 70 percent to the 75 degrees C value, 24.5 A uses the 50 percent bracket that begins at 10 conductors, and 35 A ignores adjustment entirely.2023 NEC §310.15(C)(1)

A four-wire, three-phase, 208Y/120-volt feeder supplies electric-discharge lighting, and the major portion of the load is nonlinear. How many current-carrying conductors are counted for adjustment purposes?

• a.Two
• b.Four✓
• c.Three
• d.Five

When the major portion of the load is nonlinear, harmonic currents keep the neutral loaded even under balanced conditions, so the neutral counts as a current-carrying conductor along with the three phase conductors, giving four. If the load were linear the neutral would not be counted, giving three, and the equipment grounding conductor is never counted.2023 NEC §310.15(E)

Where must a multiwire branch circuit have a means to simultaneously disconnect all ungrounded conductors?

• a.Only where the circuit supplies more than one device on a single yoke
• b.At the first outlet box on the circuit
• c.At each utilization equipment location
• d.At the point where the branch circuit originates✓

Simultaneous disconnection of all ungrounded conductors is required at the point of origin, normally by handle ties or a multipole breaker in the panelboard, so no part of the shared neutral stays energized during service work. Disconnecting at the first outlet or at the equipment does not remove the hazard back at the panel, and the single-yoke rule is a separate requirement in 210.7.2023 NEC §210.4(B)

In a dwelling unit living room, no point measured horizontally along the floor line of any wall space may be more than what distance from a receptacle outlet?

• a.12 feet
• b.6 feet✓
• c.4 feet
• d.8 feet

The 6-foot rule means a 6-foot appliance cord can reach a receptacle from any point along the wall line, which works out to a maximum spacing of 12 feet between receptacles. The 12-foot answer confuses spacing between outlets with distance from any point, and 4 or 8 feet are not code values for general wall space.2023 NEC §210.52(A)(1)

In a dwelling unit, 125-volt receptacles installed within what distance of the outside edge of a sink require GFCI protection?

• a.5 feet
• b.3 feet
• c.6 feet✓
• d.10 feet

The measurement is 6 feet from the outside edge of the sink, taken along the shortest path a cord would follow without piercing a wall or partition. The 3-foot dimension belongs to other rules such as service conductor clearance from openable windows, and 5 or 10 feet are not used for the sink measurement.2023 NEC §210.8(A)

Arc-fault circuit-interrupter protection is required for 120-volt, single-phase, 15- and 20-ampere branch circuits supplying outlets in which dwelling unit areas?

• a.Kitchens, laundry areas, bedrooms and most other habitable rooms✓
• b.Bedrooms only
• c.Unfinished basements and garages only
• d.Bathrooms and outdoor areas only

The AFCI requirement now reaches nearly every habitable area of a dwelling, including kitchens and laundry areas, not just bedrooms as in older code cycles. Bathrooms, garages and unfinished basements are the spaces typically addressed by GFCI rules instead, so limiting AFCI to those areas reverses the two protection schemes.2023 NEC §210.12(A)

A 277-volt feeder supplies three continuous lighting loads of 12, 15 and 18 amperes. What is the minimum standard feeder overcurrent device rating?

• a.50 amperes
• b.45 amperes
• c.60 amperes✓
• d.70 amperes

Total the loads first: 12 + 15 + 18 = 45 A, all continuous, so the device must be at least 45 x 1.25 = 56.25 A and the next standard rating is 60 A. The 45 A answer omits the continuous-load factor, 50 A is below the calculated minimum, and 70 A overshoots the next standard size.2023 NEC §215.3

For that same 45-ampere continuous lighting feeder, what is the minimum copper conductor size at 75 degrees C terminations?

• a.6 AWG✓
• b.8 AWG
• c.4 AWG
• d.10 AWG

The conductor must carry 45 x 1.25 = 56.25 A. In the 75 degrees C column, 8 AWG copper is 50 A and is insufficient, while 6 AWG copper at 65 A meets the requirement. 4 AWG is oversized for the stated minimum, and 10 AWG at 35 A is far below the calculated ampacity.2023 NEC §215.2(A)(1)

What is the smallest conductor size generally permitted to be installed in parallel?

• a.250 kcmil
• b.2 AWG
• c.4/0 AWG
• d.1/0 AWG✓

Conductors of 1/0 AWG and larger may be run in parallel when the paralleled sets are the same length, material, size and insulation type and terminate in the same manner. Sizes smaller than 1/0, such as 2 AWG, are not permitted to be paralleled except in a few narrow special applications, and 4/0 or 250 kcmil are simply larger than the stated minimum.2023 NEC §310.10(G)

The rule permitting the next higher standard overcurrent device rating above the conductor ampacity may be applied only where that device rating does not exceed what value?

• a.400 amperes
• b.600 amperes
• c.1,000 amperes
• d.800 amperes✓

The round-up allowance stops at 800 amperes; above that rating the overcurrent device must not exceed the ampacity of the conductors it protects. The other values are not thresholds in 240.4(B), and choosing 600 A would needlessly restrict legitimate designs in the 601 to 800 A range.2023 NEC §240.4(B)

A 200-ampere feeder uses THHN copper conductors, but the equipment terminations are rated 75 degrees C. What is the minimum conductor size?

• a.4/0 AWG
• b.2/0 AWG
• c.3/0 AWG✓
• d.250 kcmil

Because the terminations are listed for 75 degrees C, the final ampacity must be taken from the 75 degrees C column even though THHN is a 90 degrees C insulation. In that column 2/0 copper is 175 A and fails, while 3/0 copper is 200 A and matches the device. Reading the 90 degrees C column would wrongly allow 2/0, and 4/0 or 250 kcmil exceed the minimum.2023 NEC §110.14(C)(1)(b)

Using the dwelling service and feeder conductor table, what is the minimum copper conductor size for a 200-ampere single-phase dwelling service?

• a.1/0 AWG
• b.3/0 AWG
• c.4/0 AWG
• d.2/0 AWG✓

For single-phase dwelling services and the main power feeder, conductors are permitted to be sized at 83 percent of the service rating, and the dwelling table lists 2/0 copper for a 200-ampere service. The 3/0 answer is what Table 310.16 alone would require without the dwelling allowance, and 1/0 is below what the dwelling table permits.2023 NEC §310.12

What is the allowable ampacity of 4/0 AWG copper THWN in the 75 degrees C column?

• a.195 amperes
• b.205 amperes
• c.260 amperes
• d.230 amperes✓

Table 310.16 lists 4/0 copper at 230 amperes in the 75 degrees C column. The 260-ampere figure is the 90 degrees C value and may be used only as a derating base, 195 amperes is the 60 degrees C value, and 205 amperes belongs to 3/0 copper at 90 degrees C rather than 4/0.2023 NEC Table 310.16

Twelve current-carrying 12 AWG THHN copper conductors run in one raceway through a 38 degrees C ambient. What is the adjusted ampacity of each conductor?

• a.15 amperes
• b.13.65 amperes✓
• c.12 amperes
• d.10.9 amperes

Start at the 90 degrees C ampacity of 30 A, apply the 36 to 40 degrees C correction factor of 0.91, then the 50 percent adjustment for 10 through 20 conductors: 30 x 0.91 x 0.50 = 13.65 A. Answers of 15 A and 12 A apply only one of the two factors, and 10.9 A uses the 45 percent bracket that begins at 21 conductors.2023 NEC §310.15

A 5,000-watt, 240-volt single-phase electric heater operates continuously. What is the minimum standard branch-circuit overcurrent device rating?

• a.30 amperes✓
• b.20 amperes
• c.25 amperes
• d.35 amperes

The load current is 5,000 / 240 = 20.8 A, and because the load is continuous the device must be rated at least 20.8 x 1.25 = 26 A, so the next standard rating is 30 A. The 20 A and 25 A answers either ignore the continuous factor or land below the calculated minimum, and 35 A is not the next standard size above 26 A.2023 NEC §210.20(A)

What is the line current of a balanced 45 kVA, three-phase, 208-volt load?

• a.216 amperes
• b.125 amperes✓
• c.72 amperes
• d.144 amperes

For a three-phase load, I = VA / (1.732 x E) = 45,000 / (1.732 x 208) = 45,000 / 360.3, or about 125 A. The 216-ampere answer divides by the voltage alone as if the load were single-phase, 72 amperes divides by three times the voltage, and 144 amperes does not follow from the formula.

On a 20-ampere branch circuit that supplies both lighting outlets and cord-and-plug-connected equipment not fastened in place, what is the maximum load the cord-and-plug equipment may impose?

• a.12 amperes
• b.20 amperes
• c.16 amperes✓
• d.15 amperes

Cord-and-plug-connected equipment that is not fastened in place is limited to 80 percent of the branch-circuit rating when other loads share the circuit: 20 x 0.80 = 16 A. The 20-ampere answer would let the equipment consume the entire circuit, and 12 or 15 amperes are not derived from the 80 percent rule.2023 NEC §210.23

A service uses 3/0 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor?

• a.4 AWG✓
• b.6 AWG
• c.2 AWG
• d.1/0 AWG

Table 250.66 groups 2/0 and 3/0 copper service conductors together and calls for a 4 AWG copper grounding electrode conductor. The 6 AWG row applies to service conductors of 1 or 1/0 AWG, 2 AWG copper is required only above 3/0 through 350 kcmil, and 1/0 applies to service conductors above 350 through 600 kcmil.2023 NEC Table 250.66

A service is supplied by two parallel sets of 250 kcmil copper conductors per phase. What is the minimum size copper grounding electrode conductor?

• a.4 AWG
• b.2 AWG
• c.1/0 AWG✓
• d.3/0 AWG

With parallel conductors the equivalent area is the sum of the areas in one phase: 2 x 250 kcmil = 500 kcmil, which falls in the over 350 through 600 kcmil row and requires 1/0 copper. Using 2 AWG treats a single 250 kcmil conductor as the whole service, and 3/0 corresponds to services above 1,100 kcmil.2023 NEC Table 250.66

Where the grounding electrode conductor connects only to a driven ground rod, what is the largest size it is required to be?

• a.2 AWG copper
• b.4 AWG copper
• c.6 AWG copper✓
• d.1/0 AWG copper

A rod, pipe or plate electrode has a limited earth contact area, so the conductor to it is never required to be larger than 6 AWG copper regardless of what Table 250.66 would otherwise demand. The 4 AWG limit applies to a concrete-encased electrode, and larger sizes are not required for any rod connection.2023 NEC §250.66(A)

Where the grounding electrode conductor connects only to a concrete-encased electrode, what is the largest size it is required to be?

• a.2 AWG copper
• b.6 AWG copper
• c.4 AWG copper✓
• d.1/0 AWG copper

The conductor to a concrete-encased electrode is never required to be larger than 4 AWG copper. The 6 AWG cap belongs to rod, pipe and plate electrodes, and 2 AWG or 1/0 would only come from Table 250.66 before this limiting rule is applied.2023 NEC §250.66(B)

What is the minimum size copper equipment grounding conductor for a circuit protected at 60 amperes?

• a.10 AWG✓
• b.12 AWG
• c.8 AWG
• d.6 AWG

Table 250.122 is entered by the rating of the overcurrent device ahead of the circuit, and the 60-ampere row calls for 10 AWG copper. 12 AWG is listed for 20 amperes, 8 AWG for 100 amperes, and 6 AWG for 200 amperes, so all three are the wrong rows.2023 NEC Table 250.122

A 200-ampere feeder requires what minimum size copper equipment grounding conductor?

• a.3 AWG
• b.8 AWG
• c.4 AWG
• d.6 AWG✓

The 200-ampere row of Table 250.122 specifies 6 AWG copper. 8 AWG belongs to 100 amperes, 4 AWG to 300 amperes and 3 AWG to 400 amperes, so those choices come from reading adjacent rows.2023 NEC Table 250.122

What is the minimum size copper equipment grounding conductor for a 400-ampere feeder?

• a.4 AWG
• b.3 AWG✓
• c.2 AWG
• d.1 AWG

Table 250.122 lists 3 AWG copper at 400 amperes. 4 AWG is the 300-ampere value, 2 AWG the 500-ampere value and 1 AWG the 600-ampere value, so all three are one row away from the correct entry.2023 NEC Table 250.122

A 100-ampere feeder originally sized with 3 AWG copper (52,620 circular mils) is upsized to 1/0 AWG copper (105,600 circular mils) for voltage drop. What is the minimum equipment grounding conductor?

• a.4 AWG copper✓
• b.8 AWG copper
• c.6 AWG copper
• d.2 AWG copper

When ungrounded conductors are increased in size, the equipment grounding conductor must be increased in the same proportion by circular-mil area. The ratio is 105,600 / 52,620 = 2.0, and the base 100-ampere equipment grounding conductor of 8 AWG (16,510 circular mils) doubles to about 33,100 circular mils; 6 AWG has only 26,240 circular mils, so 4 AWG at 41,740 circular mils is the smallest that qualifies. Leaving it at 8 AWG ignores the proportional rule.2023 NEC §250.122(B)

A service is supplied by a single set of 500 kcmil copper ungrounded conductors. What is the minimum size copper main bonding jumper?

• a.3/0 AWG
• b.2 AWG
• c.4 AWG
• d.1/0 AWG✓

The main bonding jumper is sized from the same table used for the grounded conductor and supply-side bonding jumpers, and the over 350 through 600 kcmil row calls for 1/0 copper. The 2 AWG and 4 AWG answers come from smaller service conductor rows, and 3/0 applies to much larger services.2023 NEC §250.28(D)(1)

A service uses two parallel sets of 750 kcmil copper per phase. Using the 12.5 percent rule, what is the minimum copper main bonding jumper?

• a.250 kcmil
• b.3/0 AWG
• c.4/0 AWG✓
• d.2/0 AWG

Where the ungrounded service conductors exceed 1,100 kcmil of copper, the main bonding jumper must be at least 12.5 percent of that area: 2 x 750 = 1,500 kcmil, and 1,500 x 0.125 = 187.5 kcmil. The smallest standard conductor with at least that area is 4/0 AWG at 211.6 kcmil; 3/0 at 167.8 kcmil falls short and 250 kcmil is larger than the calculated minimum.2023 NEC §250.28(D)(2)

Service-entrance conductors supply 68 amperes of continuous load plus 120 amperes of noncontinuous load. What minimum ampacity must the conductors have?

• a.205 amperes✓
• b.188 amperes
• c.235 amperes
• d.225 amperes

Service-entrance conductors follow the same rule as feeders: noncontinuous load plus 125 percent of continuous load, or 120 + (68 x 1.25) = 120 + 85 = 205 A. The 188-ampere answer simply adds the loads, while 225 and 235 amperes apply the 125 percent factor to the entire load instead of only the continuous portion.2023 NEC §230.42(A)(1)

Using the dwelling conductor table, what is the minimum copper conductor size for a 400-ampere single-phase dwelling service?

• a.600 kcmil
• b.500 kcmil
• c.350 kcmil
• d.400 kcmil✓

The dwelling service and feeder table lists 400 kcmil copper for a 400-ampere single-phase dwelling service, reflecting the 83 percent allowance. Table 310.16 alone would push you toward 600 kcmil, and 350 kcmil is the table value for a 350-ampere service.2023 NEC §310.12

A 45 kVA, three-phase transformer has a 480-volt primary. If only primary overcurrent protection is provided at 125 percent, what is the maximum standard primary device rating?

• a.90 amperes
• b.60 amperes
• c.80 amperes
• d.70 amperes✓

Primary full-load current is 45,000 / (1.732 x 480) = 54.1 A, and 54.1 x 1.25 = 67.6 A. Because the calculated value does not correspond to a standard rating, the next higher standard size of 70 amperes is permitted. The 60-ampere answer rounds down and would nuisance trip, while 80 and 90 amperes skip past the next standard size.2023 NEC §450.3(B)

What is the secondary full-load current of a 75 kVA transformer with a 208Y/120-volt, three-phase secondary?

• a.120 amperes
• b.361 amperes
• c.208 amperes✓
• d.104 amperes

Secondary current is I = VA / (1.732 x E) = 75,000 / (1.732 x 208) = 75,000 / 360.3, or about 208 amperes. The 361-ampere answer divides by the voltage alone, 120 amperes uses the phase voltage incorrectly, and 104 amperes is roughly half the correct value.

What is the minimum length of a rod-type grounding electrode?

• a.10 feet
• b.6 feet
• c.8 feet✓
• d.5 feet

Rod and pipe electrodes must be at least 8 feet long and must have at least 8 feet in contact with the soil once installed. The 10-foot value is associated with the minimum earth contact required of a metal underground water pipe electrode, and 5 or 6 feet fall short of the rod requirement.2023 NEC §250.52(A)(5)

Where two rod electrodes are installed to make up the grounding electrode system, what is the minimum spacing between them?

• a.3 feet
• b.6 feet✓
• c.8 feet
• d.10 feet

Rods that supplement one another must be separated by at least 6 feet so their earth shells do not overlap and defeat the purpose of the second rod. The 8-foot figure is the minimum rod length rather than spacing, and 3 or 10 feet are not the code minimum.2023 NEC §250.53(A)(3)

A single ground rod does not have to be supplemented by a second electrode if its resistance to earth does not exceed what value?

• a.5 ohms
• b.25 ohms✓
• c.100 ohms
• d.1 ohm

A single rod, pipe or plate electrode must be supplemented unless it is shown to have a resistance to earth of 25 ohms or less. Values such as 5 ohms or 1 ohm come from specialized standards for communications and lightning systems, not from this general requirement, and 100 ohms is far too high.2023 NEC §250.53(A)(2)

A metal underground water pipe qualifies as a grounding electrode only if it is in direct contact with the earth for at least what length?

• a.20 feet
• b.10 feet✓
• c.8 feet
• d.5 feet

The metal underground water pipe electrode must have 10 feet or more in direct contact with the earth, including any metal well casing bonded to it. The 20-foot value belongs to the concrete-encased electrode, and 5 or 8 feet do not meet the requirement.2023 NEC §250.52(A)(1)

A concrete-encased electrode may be formed by at least 20 feet of which of the following?

• a.Bare 4 AWG copper conductor encased in the concrete footing✓
• b.Bare 6 AWG copper conductor encased in the concrete footing
• c.Insulated 4 AWG copper conductor run through the footing
• d.Bare 8 AWG copper conductor encased in the concrete footing

A concrete-encased electrode consists of at least 20 feet of bare copper not smaller than 4 AWG, or at least 20 feet of one-half inch or larger electrically conductive reinforcing bar, encased in at least 2 inches of concrete near the bottom of a footing in direct contact with earth. Smaller conductors do not qualify, and the copper must be bare so it can couple to the concrete.2023 NEC §250.52(A)(3)

When a metal underground water pipe is used as a grounding electrode, what else is required?

• a.It must be bonded to the interior metal gas piping system, which then serves as the required supplemental grounding electrode
• b.No supplement is required if the pipe is longer than 20 feet
• c.It must be supplemented by an additional electrode of a type identified in 250.52✓
• d.It may be used as the sole electrode only if its measured resistance to earth is 25 ohms or less at installation

A water pipe electrode is never allowed to stand alone because plastic repairs or dielectric fittings can silently disconnect it from earth, so it must always be supplemented by another qualifying electrode such as a rod or a concrete-encased electrode. Pipe length does not remove the requirement, gas piping is bonded but is not permitted as an electrode, and the 25-ohm test applies to rod, pipe and plate electrodes.2023 NEC §250.53(D)(2)

What is the maximum number of service disconnecting means permitted for a single set of service-entrance conductors?

• a.Eight
• b.Two
• c.Four
• d.Six✓

Up to six service disconnects are permitted, but current code requires them to be in separate enclosures or in a listed assembly with individual disconnects, each marked as a service disconnect. Two and four are below the ceiling but are not the code maximum, and eight exceeds the limit.2023 NEC §230.71

What is the minimum service disconnecting means rating for a one-family dwelling?

• a.60 amperes
• b.100 amperes✓
• c.125 amperes
• d.200 amperes

A one-family dwelling service disconnect must be rated at least 100 amperes, 3-wire. The 60-ampere minimum applies to certain limited installations and older code cycles, while 125 and 200 amperes are common design choices but exceed the code minimum.2023 NEC §230.79(C)

What is the minimum clearance above a residential driveway for overhead service conductors limited to 150 volts to ground?

• a.18 feet
• b.10 feet
• c.12 feet✓
• d.15 feet

Residential driveways and commercial areas not subject to truck traffic require 12 feet of clearance. The 10-foot clearance applies only above finished grade, sidewalks and platforms accessible to pedestrians, and 18 feet is required over public streets, alleys and roads.2023 NEC §230.24(B)

Overhead service conductors must maintain what minimum clearance from a window that is designed to be opened?

• a.6 feet
• b.5 feet
• c.10 feet
• d.3 feet✓

Service conductors must keep 3 feet of clearance from windows designed to open, doors, porches, balconies, stairs and similar locations. Conductors run above the top level of a window are considered out of reach and are exempt, and the other distances do not appear in this rule.2023 NEC §230.9(A)

Ground-fault protection of equipment is required for a solidly grounded wye service with more than 150 volts to ground when the disconnect is rated at least what value?

• a.800 amperes
• b.1,000 amperes✓
• c.600 amperes
• d.1,200 amperes

The threshold is a service disconnect rated 1,000 amperes or more on a solidly grounded wye system of more than 150 volts to ground but not exceeding 1,000 volts phase-to-phase, which describes a typical 480Y/277-volt service. The 1,200-ampere figure is the maximum permitted setting of the ground-fault protection, not the threshold at which it is required.2023 NEC §230.95

How must a panelboard be protected against overcurrent?

• a.By an overcurrent device rated at 125 percent of the panelboard rating
• b.By the sum of the branch-circuit devices installed in it
• c.By an overcurrent device having a rating not greater than the panelboard rating✓
• d.No separate protection is required if the feeder conductors are properly sized

Each panelboard must be protected by an overcurrent device rated no higher than the panelboard rating, located either in the panelboard itself as a main or ahead of it in the feeder. Summing the branch devices routinely exceeds the panelboard rating because of diversity, and no code rule allows protecting a panelboard at 125 percent of its rating.2023 NEC §408.36

On the load side of the service disconnecting means, what is the general rule for using the grounded neutral conductor to ground equipment enclosures?

• a.It is permitted only in dwelling units
• b.It is permitted where the grounded neutral conductor is at least 6 AWG copper and runs directly to the equipment
• c.It is permitted in any panelboard or subpanel that is supplied directly from the service equipment enclosure
• d.It is not permitted; a separate equipment grounding conductor must be used✓

Downstream of the service disconnect the neutral and the equipment grounding conductor must be kept separate so that normal load current does not travel on enclosures and raceways. Bonding them together at a subpanel creates parallel neutral paths and objectionable current, and neither conductor size nor occupancy type changes this general prohibition.2023 NEC §250.142(B)

A dry-type transformer rated 112.5 kVA or less is installed indoors. What is the minimum separation from combustible material unless it is separated by a fire-resistant heat-insulating barrier?

• a.3 inches
• b.6 inches
• c.12 inches✓
• d.18 inches

Dry-type transformers of 112.5 kVA or less must be at least 12 inches from combustible material unless separated by a fire-resistant, heat-insulating barrier or unless the unit is completely enclosed except for ventilating openings. The smaller clearances listed belong to other rules such as recessed luminaire and insulation spacing, not to transformer installation.2023 NEC §450.21(A)

A box contains six 12 AWG conductors, one internal cable clamp and one duplex receptacle, all 12 AWG. What minimum box volume is required?

• a.20.25 cubic inches✓
• b.13.5 cubic inches
• c.18.0 cubic inches
• d.22.5 cubic inches

Count six conductors, one allowance for all internal clamps and two allowances for the device yoke, giving 9 volume allowances. Each 12 AWG allowance is 2.25 cubic inches, so 9 x 2.25 = 20.25 cubic inches. Counting only the conductors gives 13.5 cubic inches, and forgetting that a yoke counts as two conductors gives 18.0 cubic inches.2023 NEC §314.16(B)

A device box has three 14-2 NM cables with equipment grounding conductors entering through internal clamps, and one single-pole switch is installed. What minimum box volume is required?

• a.20.0 cubic inches✓
• b.18.0 cubic inches
• c.16.0 cubic inches
• d.22.5 cubic inches

Six insulated conductors count individually, all equipment grounding conductors together count as one, all internal clamps together count as one, and the switch yoke counts as two, for 10 allowances. At 2.00 cubic inches for 14 AWG, 10 x 2.00 = 20.0 cubic inches. The 18.0 answer misses one allowance, 16.0 omits both the clamp and grounding allowances, and 22.5 uses the 12 AWG allowance by mistake.2023 NEC §314.16(B)

What is the minimum trade size of EMT required for nine 12 AWG THHN conductors?

• a.One-half inch✓
• b.Three-quarter inch
• c.One inch
• d.One and one-quarter inch

Annex C, Table C1 shows that one-half inch EMT accepts nine 12 AWG THHN conductors, exactly meeting the requirement. Three-quarter inch EMT holds sixteen and one inch holds twenty-six, so both are larger than the minimum. Annex C may be used directly whenever all conductors are the same size and insulation type.2023 NEC Annex C, Table C1

When more than two conductors are installed in a raceway, what is the maximum permitted percentage of the raceway cross-sectional area they may occupy?

• a.53 percent
• b.31 percent
• c.40 percent✓
• d.60 percent

Chapter 9, Table 1 allows 53 percent fill for one conductor, 31 percent for exactly two conductors and 40 percent for three or more. The 60 percent value applies only to a nipple not exceeding 24 inches in length between boxes or enclosures.2023 NEC Chapter 9, Table 1

A short raceway nipple no longer than 24 inches connects two enclosures. What fill percentage is permitted?

• a.31 percent
• b.40 percent
• c.53 percent
• d.60 percent✓

Notes to Chapter 9, Table 1 permit a nipple not exceeding 24 inches in length to be filled to 60 percent of its total cross-sectional area, because heat buildup and pulling friction are both minimal over such a short run. The 40, 53 and 31 percent values are the normal fills for three or more, one, and two conductors respectively.2023 NEC Chapter 9, Table 1, Note 4

Four 3/0 AWG THWN conductors, each 0.2679 square inch in area, are pulled into rigid metal conduit. What is the minimum trade size?

• a.2 inch✓
• b.1 and 1/2 inch
• c.2 and 1/2 inch
• d.1 and 1/4 inch

Total conductor area is 4 x 0.2679 = 1.0716 square inches, and with more than two conductors only 40 percent of the raceway may be filled. One and one-half inch RMC allows only about 0.81 square inch at 40 percent, which is too little, while 2 inch RMC allows about 1.34 square inches and is adequate. Two and one-half inch is larger than the calculated minimum.2023 NEC Chapter 9, Table 4

What is the minimum cover for a direct-buried UF cable installed in a residential yard on a 120-volt, 20-ampere circuit that is NOT GFCI protected?

• a.18 inches
• b.24 inches✓
• c.12 inches
• d.6 inches

Direct-buried cables and conductors under all locations not otherwise covered require 24 inches of cover. The 12-inch reduction applies only to residential branch circuits rated 120 volts or less, 20 amperes or less, and provided with GFCI protection, so removing the GFCI removes the reduction. The 6-inch and 18-inch values belong to metal and nonmetallic raceways respectively.2023 NEC Table 300.5

What is the minimum burial cover for rigid metal conduit installed underground in a location not otherwise specified?

• a.18 inches
• b.12 inches
• c.6 inches✓
• d.24 inches

Rigid metal conduit and intermediate metal conduit are permitted at 6 inches of cover because the metal wall provides its own physical protection. Nonmetallic raceways listed for direct burial require 18 inches, direct-buried cable requires 24 inches, and 12 inches applies to GFCI-protected residential branch circuits.2023 NEC Table 300.5

What is the minimum burial cover for a nonmetallic raceway listed for direct burial without concrete encasement, installed under a lawn?

• a.18 inches✓
• b.6 inches
• c.24 inches
• d.12 inches

Listed nonmetallic raceways buried without concrete encasement require 18 inches of cover in locations not otherwise specified. Metal conduit needs only 6 inches, direct-buried cable needs 24 inches, and 12 inches applies to GFCI-protected 120-volt residential branch circuits.2023 NEC Table 300.5

A GFCI-protected 120-volt, 20-ampere residential branch circuit is direct buried in a yard. What is the minimum cover?

• a.18 inches
• b.6 inches
• c.12 inches✓
• d.24 inches

Residential branch circuits rated 120 volts or less and 20 amperes or less that have GFCI protection may be buried with only 12 inches of cover, because a ground fault from a dig-in will clear immediately. Without GFCI protection the general 24-inch requirement applies, and the 6- and 18-inch values belong to metal and nonmetallic raceways.2023 NEC Table 300.5

How must electrical metallic tubing be secured and supported on a normal horizontal run?

• a.Secured within 3 feet of each box and supported at least every 10 feet✓
• b.Secured within 12 inches of each box and supported every 4 and 1/2 feet
• c.Secured within 3 feet of each box and supported every 6 feet
• d.Support is required only every 10 feet with no requirement near boxes

EMT must be securely fastened within 3 feet of every box, cabinet or termination and supported at intervals not exceeding 10 feet. The 12-inch and 4 and 1/2-foot figures belong to Type NM and Type AC cable, and the 6-foot interval is the MC cable support spacing.2023 NEC §358.30(A)

How must Type NM cable be supported where it enters a box equipped with cable clamps?

• a.Secured within 8 inches of each outlet box or fitting and supported at intervals not exceeding 6 feet along the run
• b.Secured within 12 inches of the box and supported at least every 4 and 1/2 feet✓
• c.Secured within 3 feet of the box and supported every 10 feet
• d.Secured within 12 inches of each box and supported at intervals not exceeding 6 feet, matching the rule for Type MC cable

Type NM cable is secured within 12 inches of each box, cabinet or fitting and supported at intervals not exceeding 4 and 1/2 feet. The 8-inch figure applies to a single-gang nonmetallic box without clamps, the 3-foot and 10-foot values are EMT, and the 6-foot interval belongs to MC cable.2023 NEC §334.30

At what maximum interval must Type MC cable be supported and secured?

• a.Every 3 feet, and within 12 inches of every termination
• b.Every 4 and 1/2 feet, and within 12 inches of every termination
• c.Every 10 feet, and within 3 feet of every termination
• d.Every 6 feet, and within 12 inches of every termination✓

Type MC cable is secured at intervals not exceeding 6 feet and within 12 inches of every box, cabinet or fitting where the cable terminates. The 4 and 1/2-foot interval belongs to Types NM and AC, and the 10-foot interval belongs to EMT and other rigid raceways.2023 NEC §330.30

At what maximum interval must Type AC cable be supported?

• a.Every 6 feet
• b.Every 4 and 1/2 feet✓
• c.Every 10 feet
• d.Every 3 feet

Type AC armored cable is supported at intervals not exceeding 4 and 1/2 feet and secured within 12 inches of each termination. The 6-foot figure is for Type MC cable and 10 feet is for EMT, so mixing the cable types is the usual source of error here.2023 NEC §320.30

What is the maximum support spacing for a 1-inch trade size rigid PVC conduit?

• a.6 feet
• b.5 feet
• c.3 feet✓
• d.10 feet

PVC expands and sags with temperature, so support spacing depends on trade size: one-half through 1 inch is supported every 3 feet, 1 and 1/4 through 2 inch every 5 feet, and larger sizes at progressively longer intervals. The 10-foot spacing belongs to EMT and rigid metal conduit, which are far stiffer.2023 NEC §352.30(B)

What is the maximum total amount of bend permitted in one run of EMT between pull points?

• a.270 degrees
• b.180 degrees
• c.360 degrees✓
• d.540 degrees

No more than the equivalent of four quarter bends, or 360 degrees total, is permitted between pull points such as conduit bodies and boxes, because friction rises sharply with each bend. The same 360-degree limit appears in the articles for rigid metal conduit and PVC, so it is worth memorizing once.2023 NEC §358.26

A cable passes through a bored hole in a wood stud. If the edge of the hole is less than 1 and 1/4 inches from the nearest edge of the stud, what is required?

• a.The cable must be removed and rerouted through a notch cut into the edge of the wood stud rather than the bored hole
• b.A steel plate or bushing at least 1/16 inch thick installed to protect the cable✓
• c.A listed nonmetallic sleeve of any thickness
• d.Nothing additional is required, provided that the cable installed in the bored hole is Type MC or Type AC armored cable

When the required 1 and 1/4-inch setback cannot be maintained, a steel plate, sleeve or bushing at least 1/16 inch thick must cover the area of the wire so a drywall screw or nail cannot reach it. Notching is more damaging to the stud and creates the same exposure, and nonmetallic sleeves do not satisfy this rule.2023 NEC §300.4(A)(1)

A pull box is used for a straight pull, and the largest raceway entering it is 3 inch trade size. What is the minimum required length of the box in the direction of the pull?

• a.18 inches
• b.24 inches✓
• c.12 inches
• d.36 inches

For straight pulls, the box length must be at least eight times the trade size of the largest raceway: 8 x 3 = 24 inches. The 18-inch answer uses a factor of six, which applies to angle and U pulls, and 12 inches uses a factor of four that appears nowhere in the rule.2023 NEC §314.28(A)(1)

An angle pull box has one 2-inch raceway and one 1-inch raceway entering the same wall, with conductors turning 90 degrees. What is the minimum distance from that wall to the opposite wall?

• a.24 inches
• b.12 inches
• c.16 inches
• d.13 inches✓

For angle pulls the distance is six times the trade size of the largest raceway plus the sum of the diameters of the other raceways on the same wall: (6 x 2) + 1 = 13 inches. The 12-inch answer forgets to add the additional raceway, and 24 inches applies the straight-pull factor of eight.2023 NEC §314.28(A)(2)

How must liquidtight flexible metal conduit be secured on a normal run?

• a.Within 12 inches of each box and at intervals not exceeding 6 feet
• b.Within 3 feet of each box and at intervals not exceeding 10 feet
• c.Within 12 inches of each box or fitting and at intervals not exceeding 4 and 1/2 feet✓
• d.Support is not required for lengths of 6 feet or less in any application

LFMC is secured within 12 inches of each box, cabinet or fitting and supported at intervals not exceeding 4 and 1/2 feet. Certain short lengths used for flexibility or for connections to luminaires are exempt, but that exemption is narrow and does not apply to ordinary runs, and the 10-foot spacing belongs to rigid raceways.2023 NEC §350.30(A)

How many 12 AWG conductors may be installed in a 4-11/16 inch by 2-1/8 inch square box with a volume of 42.0 cubic inches, assuming no clamps, devices or fittings?

• a.21
• b.20
• c.16
• d.18✓

Each 12 AWG conductor requires 2.25 cubic inches, so 42.0 / 2.25 = 18.67, and the count must be rounded down to 18 whole conductors. The 21-conductor answer uses the 14 AWG allowance of 2.00 cubic inches, and 20 comes from rounding up rather than down.2023 NEC §314.16(A)

Direct-buried conductors emerging from grade must be protected by an approved enclosure or raceway from below grade to what height?

• a.8 feet above finished grade✓
• b.6 feet above finished grade
• c.10 feet above finished grade
• d.4 feet above finished grade

Protection must extend from below grade to at least 8 feet above finished grade, and the underground portion must reach at least 18 inches below grade. Six feet leaves the conductors within easy reach of damage, and neither 4 nor 10 feet is the code value.2023 NEC §300.5(D)(1)

What is the maximum fill percentage when exactly two conductors are installed in a raceway?

• a.40 percent
• b.31 percent✓
• c.53 percent
• d.60 percent

Two conductors are limited to 31 percent fill, a lower figure than the 40 percent allowed for three or more, because two round conductors of similar size can jam in a bend and damage insulation during the pull. One conductor may fill 53 percent, and 60 percent applies only to a nipple 24 inches or shorter.2023 NEC Chapter 9, Table 1

What is the minimum trade size of EMT required for twenty-four 12 AWG THHN conductors?

• a.One inch✓
• b.Three-quarter inch
• c.One and one-quarter inch
• d.One and one-half inch

Annex C, Table C1 shows one inch EMT accepts twenty-six 12 AWG THHN conductors, so twenty-four fit. Three-quarter inch holds only sixteen and is too small, while one and one-quarter inch holds far more than needed. Remember that twenty-four current-carrying conductors would also trigger a 45 percent ampacity adjustment.2023 NEC Annex C, Table C1

Conductors installed in an underground raceway in a wet location must have which characteristic?

• a.A nylon jacket, which by itself qualifies the conductor for wet locations
• b.Any thermoplastic insulation, since the raceway keeps water out
• c.Insulation rated 90 degrees C, regardless of wet-location listing
• d.Insulation listed for use in wet locations, such as THWN or THWN-2✓

Raceways in underground and other wet locations are considered wet inside, so the conductors must carry a wet-location listing such as THWN, THWN-2 or XHHW. The W in the type designation is what matters; plain THHN without the dual THWN-2 marking is a dry- and damp-location conductor, and a temperature rating or nylon jacket alone does not confer a wet-location listing.2023 NEC §310.10(C)

A 25-horsepower, 460-volt, three-phase squirrel-cage motor has a table full-load current of 34 amperes. Using 75 degrees C terminations and copper, what is the minimum branch-circuit conductor size?

• a.6 AWG
• b.10 AWG
• c.8 AWG✓
• d.4 AWG

Single-motor branch-circuit conductors must carry at least 125 percent of the table full-load current: 34 x 1.25 = 42.5 A. In the 75 degrees C column, 10 AWG copper is 35 A and fails, while 8 AWG at 50 A is adequate. Sizes 6 and 4 AWG exceed the calculated minimum.2023 NEC §430.22

That same motor has a nameplate full-load current of 32 amperes and a marked service factor of 1.15. What is the maximum separate overload device rating?

• a.36.8 amperes
• b.40 amperes✓
• c.42.5 amperes
• d.32 amperes

Overload protection is based on the nameplate current, not the table value, and a service factor of 1.15 or greater permits 125 percent: 32 x 1.25 = 40 A. The 36.8-ampere answer applies the 115 percent factor used for motors with no marked service factor or temperature rise, and 42.5 amperes wrongly applies 125 percent to the table value of 34 A.2023 NEC §430.32(A)(1)

For that 34-ampere three-phase squirrel-cage motor, what is the maximum inverse-time circuit breaker permitted for branch-circuit short-circuit and ground-fault protection, using the next standard size allowance?

• a.90 amperes✓
• b.85 amperes
• c.100 amperes
• d.70 amperes

An inverse-time breaker is permitted at 250 percent of full-load current: 34 x 2.50 = 85 A, which is not a standard rating, so the next higher standard size of 90 amperes may be used. The 100-ampere answer skips a standard size, and 70 amperes corresponds to the 175 percent dual-element fuse calculation instead.2023 NEC Table 430.52(C)(1)

For the same 34-ampere motor, what is the maximum dual-element time-delay fuse permitted at the standard percentage?

• a.60 amperes✓
• b.70 amperes
• c.50 amperes
• d.90 amperes

Dual-element time-delay fuses are permitted at 175 percent of full-load current: 34 x 1.75 = 59.5 A, and because that is not a standard rating the next standard size of 60 amperes is used. The 90-ampere answer belongs to the inverse-time breaker at 250 percent, and 50 amperes falls below the calculated value.2023 NEC Table 430.52(C)(1)

A 5-horsepower, 230-volt single-phase motor has a table full-load current of 28 amperes. What is the minimum copper branch-circuit conductor at 75 degrees C terminations?

• a.10 AWG✓
• b.12 AWG
• c.8 AWG
• d.6 AWG

The conductor must carry 28 x 1.25 = 35 A. In the 75 degrees C column, 10 AWG copper is exactly 35 A and qualifies, while 12 AWG at 25 A does not. Note that 240.4(D) limits ordinary 10 AWG circuits to a 30-ampere device, but motor branch-circuit protection is sized under Article 430 instead.2023 NEC §430.22

A 30-horsepower, 460-volt three-phase motor has a table full-load current of 40 amperes. What is the minimum ampere rating of the disconnecting means?

• a.50 amperes
• b.40 amperes
• c.46 amperes✓
• d.60 amperes

The disconnecting means must have an ampere rating of at least 115 percent of the full-load current: 40 x 1.15 = 46 A, so a 60-ampere switch would be the practical selection. The 40-ampere answer omits the 115 percent factor entirely, and 50 or 60 amperes are available equipment ratings rather than the calculated minimum the question asks for.2023 NEC §430.110(A)

A feeder supplies a 25-horsepower motor (34 amperes) and a 10-horsepower motor (14 amperes), both 460 volts three phase. What minimum conductor ampacity is required?

• a.67.5 amperes
• b.60 amperes
• c.48 amperes
• d.56.5 amperes✓

Feeder conductors for several motors must carry 125 percent of the largest motor full-load current plus the sum of the other full-load currents: (34 x 1.25) + 14 = 42.5 + 14 = 56.5 A. The 48-ampere answer simply adds the two currents, and 67.5 amperes wrongly applies 125 percent to the total of both motors.2023 NEC §430.24

For that same two-motor feeder, if the largest branch-circuit protective device is 90 amperes, what is the maximum feeder overcurrent device rating?

• a.90 amperes
• b.104 amperes
• c.110 amperes
• d.100 amperes✓

The feeder device may not exceed the largest branch-circuit short-circuit and ground-fault protective device plus the sum of the full-load currents of the other motors: 90 + 14 = 104 A. Since 104 is not a standard rating and this is a maximum rather than a minimum, the next lower standard size of 100 amperes must be selected. Choosing 110 amperes would exceed the calculated ceiling.2023 NEC §430.62(A)

When sizing motor branch-circuit conductors and short-circuit protection, which current value must be used?

• a.The locked-rotor current from the nameplate code letter
• b.The motor nameplate full-load amperes
• c.The full-load current from Table 430.248 or 430.250✓
• d.The larger of nameplate current or table current

Conductor sizing, branch-circuit protection and disconnect rating are all based on the table values, which are conservative and independent of a particular manufacturer's nameplate. Nameplate current is used only for overload protection under 430.32, and locked-rotor current is used for withstand and disconnect horsepower comparisons, not for conductor sizing.2023 NEC §430.6(A)(1)

A continuous-duty motor over 1 horsepower is marked with a temperature rise of 40 degrees C but no service factor. What percentage of nameplate full-load current sets the maximum overload device?

• a.140 percent
• b.115 percent
• c.125 percent✓
• d.250 percent

Motors with a marked temperature rise not over 40 degrees C, like those with a service factor of 1.15 or greater, are permitted overload protection at 125 percent of nameplate current. The 115 percent figure applies to all other motors, 140 percent is the allowance when the initial setting will not carry the load, and 250 percent is a short-circuit protection value.2023 NEC §430.32(A)(1)

A continuous-duty motor over 1 horsepower has no marked service factor and no marked temperature rise. What is the maximum overload device rating as a percentage of nameplate full-load current?

• a.140 percent
• b.125 percent
• c.115 percent✓
• d.175 percent

Motors that carry neither a service factor of 1.15 or greater nor a marked temperature rise of 40 degrees C or less are limited to 115 percent of nameplate current, because there is less thermal margin available. The 125 percent value applies to the better-rated motors, 140 percent is the permitted increase when the motor will not start, and 175 percent is a fuse sizing percentage.2023 NEC §430.32(A)(1)

Where must a motor disconnecting means be located relative to the motor?

• a.Within 25 feet of the motor in all cases
• b.In sight from the motor location and the driven machinery, unless it is capable of being locked in the open position✓
• c.Anywhere on the same floor level as the motor
• d.In sight from the motor controller only, on the theory that the controller disconnect is always sufficient and that no separate in-sight rule applies to the motor itself

A disconnect must be in sight from the motor and driven machinery so a technician working on the equipment can see that it is open; the alternative is a disconnect elsewhere that is capable of being individually locked in the open position with the locking means remaining in place. In sight means visible and not more than 50 feet away, and a separate rule requires a disconnect in sight from the controller.2023 NEC §430.102(B)

An air conditioning condensing unit nameplate reads minimum circuit ampacity 24.6 and maximum overcurrent protective device 40. What overcurrent device must be installed?

• a.A 30-ampere device, the next standard size above the minimum circuit ampacity
• b.A 25-ampere device to match the minimum circuit ampacity
• c.A 50-ampere device sized at 125 percent of the marked maximum
• d.A device not exceeding 40 amperes✓

The marked maximum overcurrent protective device value is a ceiling set by the equipment manufacturer and tested with the unit, so the installed device must not exceed 40 amperes; a smaller device is acceptable only if it will carry the starting current. The minimum circuit ampacity of 24.6 sizes the conductors, not the protective device, and nothing permits multiplying the marked maximum by another factor.2023 NEC §440.4(B)

A hermetic refrigerant motor-compressor has a rated-load current of 20 amperes. What is the maximum branch-circuit short-circuit and ground-fault protective device at the standard 175 percent figure?

• a.60 amperes
• b.25 amperes
• c.45 amperes
• d.35 amperes✓

Protection for a motor-compressor is sized at not more than 175 percent of the rated-load current: 20 x 1.75 = 35 A, which is a standard rating. Where that device still will not carry the starting current it may be increased, but never above 225 percent, which here would be 45 amperes. A 25-ampere device is below the calculated value and would nuisance trip on start.2023 NEC §440.22(A)

For that same 20-ampere rated-load compressor supplied alone, what minimum conductor ampacity is required?

• a.35 amperes
• b.20 amperes
• c.25 amperes✓
• d.30 amperes

Branch-circuit conductors for a single motor-compressor must have an ampacity of at least 125 percent of the rated-load current or branch-circuit selection current, whichever is greater: 20 x 1.25 = 25 A, which calls for 10 AWG copper. The 35-ampere figure is the 175 percent protective device calculation, and 20 amperes omits the required multiplier entirely.2023 NEC §440.32

A surface-mounted luminaire with a completely enclosed light source is installed in a clothes closet. What is the minimum clearance to the nearest point of the defined storage space?

• a.12 inches✓
• b.6 inches
• c.3 inches
• d.18 inches

Surface-mounted luminaires with a completely enclosed light source require 12 inches of clearance from the storage space, while recessed luminaires with an enclosed light source are permitted at 6 inches because the housing is set back into the ceiling or wall. Open incandescent lamps are not permitted in clothes closets at all.2023 NEC §410.16(C)

A recessed luminaire that is NOT identified for insulation contact must maintain what minimum clearance from thermal insulation?

• a.1 inch
• b.1/2 inch
• c.6 inches
• d.3 inches✓

A non-IC recessed luminaire must be spaced at least 3 inches from thermal insulation so heat can dissipate, and insulation must not be installed above it in a way that traps heat. The 1/2-inch dimension is the required clearance from combustible materials other than the mounting surface, which is a different measurement.2023 NEC §410.116

A generator nameplate current rating is 200 amperes. What minimum conductor ampacity is required from the generator terminals to the first overcurrent device?

• a.230 amperes✓
• b.200 amperes
• c.250 amperes
• d.160 amperes

Conductors from generator terminals to the first distribution device must have an ampacity of at least 115 percent of the nameplate current rating: 200 x 1.15 = 230 A, which corresponds to 4/0 copper at 75 degrees C. The 200-ampere answer omits the factor, 250 amperes uses 125 percent, and 160 amperes derates rather than uprates.2023 NEC §445.13(A)

A photovoltaic source circuit uses modules with a rated short-circuit current of 10 amperes. What minimum conductor ampacity is required before any temperature or conduit-fill adjustments?

• a.12.5 amperes
• b.15.6 amperes✓
• c.10 amperes
• d.20 amperes

The maximum circuit current is 125 percent of the rated short-circuit current, or 10 x 1.25 = 12.5 A, and the conductor must then be sized at 125 percent of that value without adjustment factors: 12.5 x 1.25 = 15.6 A. The 12.5-ampere answer stops after only the first multiplier, and 10 amperes ignores both.2023 NEC §690.8

A motor with a service factor of 1.16 will not start because the overload device trips, even though it is sized at 125 percent of nameplate current. To what maximum percentage may the overload device be increased?

• a.140 percent✓
• b.130 percent
• c.150 percent
• d.175 percent

Where the overload device selected at the basic percentage is not sufficient to start the motor or carry the load, motors with a service factor of 1.15 or greater or a marked temperature rise of 40 degrees C or less may be increased to 140 percent of nameplate current. The 130 percent ceiling applies to all other motors, and 175 percent is a fuse percentage for short-circuit protection.2023 NEC §430.32(C)

What is the maximum non-time-delay fuse permitted for branch-circuit short-circuit and ground-fault protection of a 34-ampere three-phase squirrel-cage motor, using the next standard size allowance?

• a.110 amperes✓
• b.100 amperes
• c.90 amperes
• d.125 amperes

Non-time-delay fuses are permitted at 300 percent of full-load current: 34 x 3.00 = 102 A, which is not a standard rating, so the next standard size of 110 amperes may be used. The 90-ampere answer belongs to the inverse-time breaker at 250 percent, and 125 amperes skips a standard size.2023 NEC Table 430.52(C)(1)

A 20-horsepower, 208-volt three-phase motor has a table full-load current of 59.4 amperes. What is the minimum copper branch-circuit conductor at 75 degrees C terminations?

• a.6 AWG
• b.4 AWG✓
• c.3 AWG
• d.8 AWG

The conductor must carry 59.4 x 1.25 = 74.25 A. In the 75 degrees C column, 6 AWG copper is 65 A and falls short, while 4 AWG copper at 85 A is adequate. Choosing 3 AWG is oversized for the minimum, and 8 AWG at 50 A is well below the requirement.2023 NEC §430.22

A heating element of 30 ohms is connected across 240 volts. What current flows?

• a.8 amperes✓
• b.0.125 ampere
• c.7,200 amperes
• d.12 amperes

Ohm's law gives I = E / R = 240 / 30 = 8 amperes. The 0.125-ampere answer inverts the division, 7,200 multiplies voltage by resistance instead of dividing, and 12 amperes would require a 20-ohm element.

What power is consumed by a 120-volt load drawing 12 amperes at unity power factor?

• a.1,440 watts✓
• b.10 watts
• c.132 watts
• d.1,200 watts

Power in a resistive single-phase circuit is P = E x I = 120 x 12 = 1,440 watts. The 10-watt answer divides instead of multiplying, 132 watts adds the two values, and 1,200 watts does not follow from the given numbers.

How much power is dissipated when 5 amperes flows through a 20-ohm resistor?

• a.100 watts
• b.500 watts✓
• c.4 watts
• d.2,000 watts

Using P = I squared x R, the calculation is 5 x 5 x 20 = 500 watts. The 100-watt answer multiplies current by resistance without squaring the current, 4 watts divides the wrong way, and 2,000 watts squares the resistance instead of the current.

Three resistors of 10, 15 and 25 ohms are connected in series across 120 volts. What is the circuit current?

• a.24 amperes
• b.2.4 amperes✓
• c.4.8 amperes
• d.0.42 ampere

Series resistances add: 10 + 15 + 25 = 50 ohms, so I = 120 / 50 = 2.4 amperes. The 24-ampere answer misplaces the decimal, 4.8 amperes would result from a 25-ohm total, and 0.42 ampere inverts the division.

A 20-ohm resistor and a 30-ohm resistor are connected in parallel. What is the total resistance?

• a.50 ohms
• b.12 ohms✓
• c.25 ohms
• d.10 ohms

For two resistors in parallel, R total = (R1 x R2) / (R1 + R2) = (20 x 30) / 50 = 600 / 50 = 12 ohms. The 50-ohm answer adds them as if they were in series, and 25 ohms averages them, but total parallel resistance is always less than the smallest branch resistance.

A balanced three-phase load draws 40 amperes at 480 volts with a power factor of 0.85. What is the true power?

• a.Approximately 33.3 kilowatts
• b.Approximately 28.3 kilowatts✓
• c.Approximately 19.2 kilowatts
• d.Approximately 16.3 kilowatts

True power for a three-phase load is P = 1.732 x E x I x PF = 1.732 x 480 x 40 x 0.85, or about 28,270 watts. The 33.3-kilowatt answer omits the power factor and gives apparent power in kVA instead, 19.2 kilowatts leaves out the 1.732 factor, and 16.3 kilowatts omits both.

On a 208Y/120-volt wye system, what is the relationship between line voltage and phase voltage?

• a.Line voltage equals phase voltage divided by 1.732
• b.Line voltage equals phase voltage
• c.Line voltage equals phase voltage multiplied by 3
• d.Line voltage equals phase voltage multiplied by 1.732✓

In a wye configuration the line voltage is the square root of three times the phase voltage: 120 x 1.732 = 208 volts, while line current equals phase current. In a delta configuration the relationship reverses, with line voltage equal to phase voltage and line current equal to 1.732 times phase current.

A balanced delta-connected load has a phase current of 20 amperes. What is the line current?

• a.20 amperes
• b.Approximately 34.6 amperes✓
• c.Approximately 11.5 amperes
• d.60 amperes

In a delta connection each line conductor feeds two phase windings, so line current equals 1.732 times phase current: 20 x 1.732 = 34.6 amperes. The 20-ampere answer describes a wye connection, 11.5 amperes divides instead of multiplying, and 60 amperes triples the value rather than applying the square root of three.

A single-phase transformer has a 480-volt primary and a 120-volt secondary. If the secondary carries 100 amperes, what is the approximate primary current?

• a.50 amperes
• b.100 amperes
• c.400 amperes
• d.25 amperes✓

Voltage and current transform inversely, so the 4 to 1 voltage ratio produces a 1 to 4 current ratio: 100 / 4 = 25 amperes on the primary. Neglecting losses, the volt-amperes match on both sides, 480 x 25 = 120 x 100 = 12,000 VA. The 400-ampere answer inverts the ratio and would represent an impossible power gain.

What is the secondary full-load current of a 25 kVA single-phase transformer with a 240-volt secondary?

• a.Approximately 60 amperes
• b.Approximately 104 amperes✓
• c.Approximately 208 amperes
• d.Approximately 52 amperes

For a single-phase transformer, I = VA / E = 25,000 / 240, or about 104 amperes. The 60-ampere answer divides by 480 volts, 208 amperes divides by 120 volts, and 52 amperes is half the correct value.

A 480-volt panelboard is mounted on a wall with a grounded concrete wall directly behind the working space. What is the minimum depth of working space?

• a.2 and 1/2 feet
• b.3 feet
• c.4 feet
• d.3 and 1/2 feet✓

For nominal voltages of 151 to 600 volts to ground, Condition 2 exists when exposed live parts face a grounded surface such as a concrete or masonry wall, and the required depth is 3 and 1/2 feet. Condition 1, with no live or grounded parts opposite, requires 3 feet, and Condition 3, with exposed live parts on both sides, requires 4 feet.2023 NEC §110.26(A)(1)

What is the minimum width of working space in front of electrical equipment?

• a.30 inches in all cases regardless of equipment width
• b.30 inches, or the width of the equipment, whichever is greater✓
• c.36 inches, or the width of the equipment, whichever is greater
• d.24 inches, measured from the centerline of the equipment

The working space must be at least 30 inches wide or as wide as the equipment, whichever is greater, and it must allow all doors and hinged panels to open at least 90 degrees. The space need not be directly centered on the equipment, but it must be continuous across the full width required.2023 NEC §110.26(A)(2)

Entrances at each end of the working space are generally required for equipment rated at least what value and over 6 feet wide?

• a.1,000 amperes
• b.800 amperes
• c.1,200 amperes✓
• d.600 amperes

Equipment rated 1,200 amperes or more and over 6 feet wide containing overcurrent, switching or control devices needs an entrance at each end of the working space so a worker is never trapped behind an arcing fault. The 1,000-ampere threshold belongs to service ground-fault protection, and 800 amperes is the ceiling for the next-standard-size overcurrent rule.2023 NEC §110.26(C)(2)

The dedicated equipment space above a panelboard extends from the top of the equipment to what height?

• a.It extends all the way up to the structural ceiling in every case, with no allowance to stop at any lower height
• b.It extends only 3 feet above the top of the equipment in all cases, regardless of the height of the structural ceiling
• c.6 feet above the equipment or to the structural ceiling, whichever is lower✓
• d.6 and 1/2 feet above the finished floor

The dedicated space is the footprint of the equipment extended from the floor to a height of 6 feet above it or to the structural ceiling, whichever is lower, and no foreign piping, ducts or equipment may be installed in it. Suspended ceilings with removable panels are not considered structural ceilings, and the 6 and 1/2-foot dimension is the minimum headroom of working space, a separate requirement.2023 NEC §110.26(E)(1)

Which sequence correctly describes verifying that equipment is de-energized before beginning work?

• a.Test the meter on a known live source, test the de-energized conductors, then retest the meter on the known live source✓
• b.Test the de-energized conductors, then test the meter on a known live source
• c.Rely on the open position of the disconnect and the applied lock
• d.Test the de-energized conductors only, since the meter was checked at the start of the shift

The live-dead-live method proves the instrument is working both before and after the absence-of-voltage test, so a meter that failed during the check cannot lead a worker to treat energized conductors as safe. Locking and tagging the disconnect is required, but it does not by itself confirm that the conductors ahead of the work are actually de-energized, since backfeeds and mislabeled circuits are common.

Using the standard calculation method, what is the general lighting and general-use load for a dwelling unit with 2,000 square feet of habitable floor area, before any demand factors?

• a.4,500 volt-amperes
• b.3,000 volt-amperes
• c.6,000 volt-amperes✓
• d.9,000 volt-amperes

Table 220.12 assigns dwelling units a general lighting unit load of 3 volt-amperes per square foot, so 2,000 x 3 = 6,000 volt-amperes. The 4,500 answer uses 2.25 VA and 9,000 uses 4.5 VA, neither of which is the dwelling value in the 2023 NEC.2023 NEC Table 220.12

How much load must be included for the two required small-appliance branch circuits plus the one required laundry branch circuit of a dwelling, before demand factors are applied?

• a.3,000 volt-amperes
• b.4,500 volt-amperes✓
• c.1,500 volt-amperes
• d.6,000 volt-amperes

Each small-appliance and laundry branch circuit is calculated at 1,500 volt-amperes: two small-appliance circuits plus one laundry circuit is 3 x 1,500 = 4,500 volt-amperes. The 3,000 answer counts only the two small-appliance circuits and omits the laundry circuit.2023 NEC §220.52

A dwelling has a combined general lighting, small-appliance and laundry load of 12,000 volt-amperes. Applying the standard demand factors, what is the demand load?

• a.12,000 volt-amperes
• b.4,200 volt-amperes
• c.7,650 volt-amperes
• d.6,150 volt-amperes✓

The dwelling lighting demand table takes the first 3,000 volt-amperes at 100 percent and the remainder from 3,001 to 120,000 volt-amperes at 35 percent: 3,000 + (9,000 x 0.35) = 3,000 + 3,150 = 6,150 volt-amperes. Applying 35 percent to the whole 12,000 gives the incorrect 4,200 figure.2023 NEC Table 220.45

Using the standard demand table for household cooking appliances, what is the demand load for a single 12-kilowatt household electric range?

• a.8 kilowatts✓
• b.12 kilowatts
• c.6 kilowatts
• d.9.6 kilowatts

Column C of Table 220.55 gives a demand of 8 kilowatts for one household range rated not over 12 kilowatts, reflecting the fact that all burners and the oven are rarely at full power at once. The 9.6-kilowatt answer applies an 80 percent factor that does not appear in the table, and 12 kilowatts ignores the demand allowance entirely.2023 NEC Table 220.55

A dwelling has a single household electric clothes dryer with a nameplate rating of 4.5 kilowatts. What value must be used for the dryer load in the service calculation?

• a.4,500 volt-amperes
• b.4,000 volt-amperes
• c.5,000 volt-amperes✓
• d.3,600 volt-amperes

The load for a household electric clothes dryer is 5,000 volt-amperes or the nameplate rating, whichever is larger, so a 4,500-volt-ampere nameplate is calculated at the 5,000-volt-ampere floor. Using the nameplate 4,500 value violates the minimum, and the other figures apply factors that do not belong here.2023 NEC §220.54

A dwelling feeder supplies four fastened-in-place appliances (a disposal, a dishwasher, a water heater and a trash compactor) in addition to other loads. What demand factor may be applied to the nameplate total of these appliances?

• a.100 percent
• b.75 percent✓
• c.50 percent
• d.80 percent

Where four or more fastened-in-place appliances other than ranges, clothes dryers, space-heating and air-conditioning equipment are on the same feeder, a 75 percent demand factor may be applied to the nameplate total. With three or fewer such appliances no reduction is permitted, which is where the 100 percent answer applies.2023 NEC §220.53

Using the optional calculation method for a dwelling, the general loads total 40 kVA. What is the demand load for these general loads?

• a.40 kVA
• b.16 kVA
• c.22 kVA✓
• d.20 kVA

The optional dwelling method takes the first 10 kVA of general load at 100 percent and the remainder at 40 percent: 10 + (30 x 0.40) = 10 + 12 = 22 kVA. Applying 40 percent to the entire 40 kVA gives the incorrect 16-kVA figure.2023 NEC §220.82(B)

A commercial building has 50 general-use receptacle outlets. Using the standard method, what receptacle load must be calculated before demand factors?

• a.9,000 volt-amperes✓
• b.6,000 volt-amperes
• c.7,500 volt-amperes
• d.9,900 volt-amperes

Non-dwelling receptacle outlets are calculated at 180 volt-amperes each, where a single or multiple receptacle on one yoke counts as one outlet: 50 x 180 = 9,000 volt-amperes. The 7,500 answer uses 150 VA and 6,000 uses 120 VA, neither of which is the code value.2023 NEC §220.14(I)

When calculating a feeder or service that supplies several motors plus other loads, how is the largest motor accounted for?

• a.It is counted at 100 percent of its full-load current, exactly the same as all of the other motors in the calculation
• b.It is counted at 80 percent of its full-load current because of assumed diversity among the connected motors
• c.At 115 percent of its full-load current
• d.By adding 25 percent of its full-load current on top of the summed loads✓

Motor loads are calculated per Article 430, which requires the feeder to carry 125 percent of the largest motor plus the full-load currents of the remaining motors; in a combined load calculation this is applied by adding an extra 25 percent of the largest motor to the total. The 115 percent figure is the motor disconnect rating, not the conductor calculation.2023 NEC §220.50

Which of the following dwelling-unit locations requires GFCI protection for 125-volt, 15- and 20-ampere receptacles?

• a.A wall receptacle in a second-floor bedroom
• b.A receptacle in an unfinished basement✓
• c.A receptacle in a first-floor hallway
• d.A receptacle in a bedroom clothes closet

Section 210.8(A) lists unfinished basements among the dwelling areas requiring GFCI protection, along with bathrooms, garages, outdoors, crawl spaces, kitchens and laundry areas. Bedrooms and hallways are addressed by AFCI rather than GFCI requirements, so they are not on the GFCI list.2023 NEC §210.8(A)

Using the standard demand table for household cooking appliances, what is the demand load for three 12-kilowatt household electric ranges supplied by one feeder?

• a.24 kilowatts
• b.8 kilowatts
• c.14 kilowatts✓
• d.22 kilowatts

Column C of Table 220.55 gives a demand of 14 kilowatts for three ranges rated not over 12 kilowatts each, applying diversity across the appliances. The 24-kilowatt answer would result from a naive sum with a partial factor, and 8 kilowatts is the single-range value.2023 NEC Table 220.55

The interior metal water piping system of a building must be bonded to the service equipment. How is the required bonding jumper sized?

• a.From Table 250.66, based on the size of the service-entrance conductors✓
• b.From Table 250.122, based on the rating of the overcurrent device protecting the largest service conductor
• c.Always 6 AWG copper regardless of service size
• d.From Table 310.16, based on the service ampacity and the temperature rating of the terminations used

The bonding jumper for the interior metal water piping system is sized from Table 250.66 using the ungrounded service-entrance conductors, the same table used for the grounding electrode conductor. Table 250.122 sizes equipment grounding conductors by overcurrent device and does not apply to this bond.2023 NEC §250.104(A)(1)

For a separately derived system such as a transformer secondary, where is the system bonding jumper permitted to be installed?

• a.At every downstream panelboard
• b.Only at the main service disconnecting means of the building and never at the transformer, panelboard, or any other point of the separately derived system
• c.At the source of the separately derived system or at the first disconnecting means, but at only one of those points✓
• d.It is not required for separately derived systems

A separately derived system requires a single system bonding jumper connecting the grounded conductor to the equipment grounding system, installed either at the source or at the first disconnecting means but at only one location. Installing it at more than one point creates parallel neutral paths, and omitting it leaves no effective fault-clearing path for the derived system.2023 NEC §250.30(A)(1)

A single-family dwelling has a calculated demand load of 21,600 volt-amperes on a 240-volt, single-phase service. What is the minimum service disconnecting means rating permitted?

• a.90 amperes
• b.100 amperes✓
• c.125 amperes
• d.60 amperes

The calculated current is 21,600 / 240 = 90 amperes, but the service disconnecting means for a one-family dwelling must be rated at least 100 amperes, so the code floor governs. Selecting 90 amperes satisfies the calculation but violates the 100-ampere minimum, and 125 amperes exceeds the required minimum.2023 NEC §230.79(C)

The grounded (neutral) service conductor also serves as the effective ground-fault current path back to the utility. It must be sized not smaller than what?

• a.The equipment grounding conductor from Table 250.122
• b.6 AWG copper in all cases
• c.One-half the ungrounded conductor size
• d.The grounding electrode conductor value from Table 250.102(C)(1)✓

Because there is no main bonding jumper ahead of the service, the grounded conductor must carry any fault current back to the source, so it may not be smaller than the value from Table 250.102(C)(1), which mirrors Table 250.66. Sizing it from the equipment grounding conductor table would leave it too small for that duty.2023 NEC §250.24(C)

At service equipment, why are standard locknuts and bushings alone not adequate where service raceways connect through concentric or eccentric knockouts?

• a.They are in fact adequate by themselves, so no additional bonding means, jumpers, or listed fittings are needed where service raceways connect through concentric or eccentric knockouts
• b.Because service raceways must always be nonmetallic
• c.Because service bonding requires bonding jumpers, bonding bushings or other listed bonding-type fittings to ensure a low-impedance path✓
• d.Because only exothermic welding is permitted at a service

Service raceways and enclosures must be bonded by an approved means such as bonding jumpers, bonding-type locknuts or bushings, since standard locknuts across concentric or eccentric knockouts cannot be relied on for the high fault current available ahead of the service overcurrent device. Downstream of the service, standard locknuts are generally acceptable.2023 NEC §250.92(B)

A grounding electrode conductor is run from the service to a driven ground rod. What is the rule regarding splices in that conductor?

• a.Any listed split-bolt connector may be used
• b.It must be installed in one continuous length unless spliced by irreversible compression connectors, exothermic welding or connections to busbars✓
• c.Up to three twist-on wire connector splices are permitted along the run, provided that each connection is made accessible and the conductor is not reduced in size at any of the splice points
• d.Splices are permitted only inside accessible junction boxes

A grounding electrode conductor must be continuous, and where a splice is necessary it is permitted only by irreversible compression connectors listed for the purpose, exothermic welding, or bolting to busbars. Ordinary split-bolts and twist-on connectors are reversible and are not acceptable for this conductor.2023 NEC §250.64(C)

How is the load on a feeder or service neutral (grounded) conductor determined?

• a.By the maximum unbalanced load, the maximum net current between the neutral and any one ungrounded conductor✓
• b.By the sum of all ungrounded conductor currents
• c.It is always the same size as the ungrounded conductors
• d.By taking 125 percent of the load on the largest single ungrounded conductor and applying that resulting value to the neutral conductor

The neutral carries only the imbalance among the phase conductors, so its calculated load is the maximum unbalanced load, defined as the maximum net current between the neutral and any one ungrounded conductor. Loads such as 240-volt line-to-line appliances place no current on the neutral at all.2023 NEC §220.61(A)

A demand factor may be applied to the portion of a feeder neutral load that exceeds what value?

• a.100 amperes
• b.150 amperes
• c.200 amperes✓
• d.400 amperes

For a feeder or service, the portion of the maximum unbalanced neutral load that exceeds 200 amperes may be taken at 70 percent, recognizing the diversity of line-to-neutral loads at higher currents. This reduction does not apply to nonlinear loads on a wye system, where the neutral can be as heavily loaded as the phases.2023 NEC §220.61(B)

A junction box contains four 14 AWG conductors and two 12 AWG conductors, with no devices, clamps or fittings. What minimum box volume is required?

• a.12.5 cubic inches✓
• b.13.5 cubic inches
• c.11.0 cubic inches
• d.15.0 cubic inches

Each conductor is counted at the volume allowance for its own size: four 14 AWG at 2.00 cubic inches is 8.0, and two 12 AWG at 2.25 cubic inches is 4.5, for a total of 12.5 cubic inches. Using 2.25 for every conductor gives the incorrect 13.5 figure.2023 NEC §314.16(B)(1)

What is the minimum distance a 125-volt, 15- or 20-ampere receptacle must be located from the inside wall of a permanently installed pool?

• a.10 feet
• b.6 feet✓
• c.5 feet
• d.3 feet

General-use receptacles must be at least 6 feet from the inside walls of a permanently installed pool, measured along the shortest path a cord would follow. At least one required receptacle must also be located between 6 and 20 feet from the pool, and receptacles serving pool equipment must be GFCI protected.2023 NEC §680.22(A)(1)

A location is classified as Class I, Division 1 when which condition exists?

• a.Combustible dust in ignitible concentrations is present in the surrounding air only during infrequent abnormal operating conditions
• b.Easily ignitible fibers or flyings are handled or stored but are not normally likely to become suspended in the air
• c.Ignitible concentrations of flammable gases or vapors can exist under normal operating conditions✓
• d.Flammable liquids are stored only in sealed containers

Class I covers flammable gases and vapors, and Division 1 means ignitible concentrations can exist under normal operating conditions or frequently because of repair, maintenance or leakage. Combustible dust is Class II and ignitible fibers are Class III, so those descriptions point to different classifications.2023 NEC §500.5(B)(1)

A 15-ampere, 125-volt receptacle is installed outdoors in a wet location. What type of cover is required?

• a.Any weatherproof cover, effective only when the receptacle is unused
• b.A standard thermoplastic wall plate
• c.A cover that is weatherproof only when no plug is inserted
• d.A cover that is weatherproof whether or not an attachment plug is inserted✓

Receptacles in wet locations must have an enclosure that is weatherproof whether or not an attachment plug is inserted, commonly an in-use or bubble cover, because cords are often left plugged in outdoors. A cover that seals only when empty meets the lesser damp-location standard, not the wet-location rule.2023 NEC §406.9(B)(1)

In a dwelling unit, 125-volt and 250-volt, 15- and 20-ampere receptacles must generally be what type?

• a.Isolated-ground type
• b.Listed tamper-resistant type✓
• c.Hospital-grade type
• d.Twist-lock type

To prevent children from inserting objects into energized slots, these receptacles in dwelling units must be listed tamper-resistant. Hospital-grade and isolated-ground receptacles address other concerns and are not the general dwelling requirement.2023 NEC §406.12

Type NM (nonmetallic-sheathed) cable is NOT permitted in which of the following?

• a.Wet or damp locations✓
• b.The framed walls of a one-family dwelling
• c.An exposed dry run in the basement of a dwelling
• d.A concealed dry run in an attic

Type NM cable is prohibited in wet or damp locations because its sheath is not rated for moisture, and it may not be embedded in concrete or used where exposed to corrosive fumes. It remains a standard method for the dry, concealed and exposed interior wiring of dwellings.2023 NEC §334.12(B)

Flexible metal conduit (FMC) may serve as an equipment grounding conductor only where the total length in the ground-return path does not exceed 6 feet and which additional condition is met?

• a.The conduit is at least 1 inch trade size
• b.The circuit voltage does not exceed 50 volts
• c.The circuit conductors are protected at 20 amperes or less and the fittings are listed for grounding✓
• d.A separate equipment bonding jumper is installed on the outside of the conduit for its full length and terminated at both ends

FMC qualifies as an equipment grounding conductor only when the ground-return length is 6 feet or less, the overcurrent protection is 20 amperes or less, and the fittings are listed for grounding. Where any of these limits is exceeded, a separate equipment grounding conductor must be installed.2023 NEC §250.118(6)

The equipotential bonding grid required around a permanently installed pool must be formed with which conductor?

• a.6 AWG stranded aluminum
• b.8 AWG solid copper✓
• c.10 AWG solid copper
• d.4 AWG insulated copper

The equipotential bonding required around a pool uses a solid copper conductor not smaller than 8 AWG to tie together the reinforcing steel, coping, deck, ladders and equipment so that everyone stands at the same potential. Aluminum is not permitted for this bond, and 10 AWG is undersized.2023 NEC §680.26(B)

A box or conduit body installed in a wet location must meet which requirement?

• a.It may be any standard indoor box, provided that a weatherproof gasket is added between the box and the cover plate
• b.It must be completely filled with an approved duct seal compound to keep out all moisture and condensation
• c.It must be nonmetallic only
• d.It must be listed for wet locations and be installed so water cannot enter or accumulate within it✓

Boxes and fittings in damp or wet locations must be placed or equipped so water cannot enter or accumulate inside, and in wet locations they must be listed for that use. Both metallic and nonmetallic boxes are permitted if properly listed and installed, so material alone does not satisfy the rule.2023 NEC §314.15

How many running overload protective devices are required for a three-phase alternating-current motor?

• a.One
• b.Two
• c.Three, one in each phase✓
• d.Four

Table 430.37 requires a three-phase motor to have an individual overload device in each of the three ungrounded conductors, so that a single-phasing condition, which overloads the remaining windings, is detected. One or two devices could miss an overload on an unprotected phase.2023 NEC §430.37

A 25-kVA, single-phase transformer has a 480-volt primary and is protected by primary overcurrent protection only, sized at 125 percent. With a primary full-load current of 9 amperes or more, what is the maximum standard primary overcurrent device rating?

• a.60 amperes
• b.50 amperes
• c.65 amperes
• d.70 amperes✓

Primary current is 25,000 / 480 = 52.1 amperes, and 52.1 x 1.25 = 65.1 amperes. Because that value is not a standard rating, the next higher standard size of 70 amperes is permitted. 65 amperes is not a standard overcurrent device rating, and 60 amperes would be below the calculated value.2023 NEC §450.3(B)

On a feeder supplying several motors, 125 percent is applied to which motor's full-load current?

• a.The highest-rated motor, meaning the one with the largest full-load current✓
• b.The smallest motor
• c.Every motor on the feeder
• d.The motor with the highest horsepower nameplate regardless of current

Feeder conductors are sized at 125 percent of the largest motor full-load current plus the sum of the full-load currents of the other motors, and the largest motor is the one with the highest rated full-load current per 430.17. Applying 125 percent to every motor over-sizes the feeder.2023 NEC §430.24

An outlet box used as the sole support of a ceiling-suspended paddle fan must meet what requirement?

• a.Any 4-inch box rated for 50 pounds is acceptable
• b.It must be listed and marked for the purpose of supporting a fan, and fans over 70 pounds require additional independent support✓
• c.It must be a nonmetallic box only
• d.No special outlet box is required as long as two long wood screws are driven through the box and directly into the structural framing member above

Outlet boxes are not permitted as the sole support of a ceiling fan unless they are listed and marked for that purpose, and a fan exceeding 70 pounds must be supported independently of the box. A standard lighting outlet box is not rated for the dynamic load of a rotating fan.2023 NEC §314.27(C)

Within what zone measured from the rim of a bathtub or the threshold of a shower stall are hanging luminaires and ceiling-suspended paddle fans generally prohibited?

• a.2 feet horizontally and 6 feet vertically
• b.5 feet horizontally and 10 feet vertically
• c.3 feet horizontally and 8 feet vertically✓
• d.6 feet horizontally and 8 feet vertically

Cord-connected luminaires, hanging luminaires, track lighting, pendants and ceiling fans are not permitted within a zone of 3 feet horizontally and 8 feet vertically from the top of the bathtub rim or shower threshold, keeping them out of reach of a wet person. Fixed luminaires outside that zone are acceptable.2023 NEC §410.10(D)

A cord-and-plug-connected room air conditioner is the only load on its branch circuit. Its total rating must not exceed what percentage of the branch-circuit rating?

• a.100 percent
• b.80 percent✓
• c.50 percent
• d.125 percent

Where the room air conditioner is the only load on the circuit, its marked rating may not exceed 80 percent of the branch-circuit rating. If lighting units or other appliances are also supplied by the circuit, that ceiling drops to 50 percent.2023 NEC §440.62(B)

An indoor dry-type transformer rated more than 112.5 kVA must generally be installed in what manner?

• a.Installed no less than six inches away from any combustible material, or otherwise provided with a listed thermal barrier, with no requirement for a fire-resistant transformer room no matter how large the unit is
• b.On a raised concrete pad only
• c.Within sight of the main service
• d.In a transformer room of fire-resistant construction, unless it has Class 155 or higher insulation and is separated from combustibles by a barrier or by adequate distance✓

Dry-type transformers over 112.5 kVA installed indoors must be in a transformer room of fire-resistant construction, with exceptions for units having Class 155 or higher insulation that are either completely enclosed or separated from combustible material by a fire-resistant barrier or by clearance. Units of 112.5 kVA or less instead follow the 12-inch clearance rule.2023 NEC §450.21(B)

As defined in Article 100, ampacity is best described as which of the following?

• a.The maximum current a conductor can carry continuously under the conditions of use without exceeding its temperature rating✓
• b.The current that will instantly melt the conductor
• c.The rated current of the overcurrent device protecting the conductor, taken directly from the marking on the breaker or fuse without regard to installation conditions
• d.The current at which voltage drop reaches 3 percent

Article 100 defines ampacity as the maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. It is a property of the conductor and its environment, not the rating of the protective device ahead of it.2023 NEC Art. 100

Under the Article 100 definitions, what does it mean for metal parts to be bonded?

• a.Connected to the earth through a ground rod
• b.Insulated from all other metal parts
• c.Connected together to establish electrical continuity and conductivity✓
• d.Painted to prevent corrosion

Bonding means connecting parts together to establish electrical continuity and conductivity, which is what allows fault current to return to the source and open the overcurrent device. Connecting a part to the earth is grounding, a related but distinct concept.2023 NEC Art. 100

Three 30-ohm resistors are connected in parallel. What is the total resistance?

• a.90 ohms
• b.10 ohms✓
• c.30 ohms
• d.15 ohms

For equal resistors in parallel, total resistance equals the value of one resistor divided by the number of resistors: 30 / 3 = 10 ohms. The 90-ohm answer adds them as if in series, and total parallel resistance is always less than the smallest branch.

How much energy does a 1,500-watt electric heater consume when operated continuously for 4 hours?

• a.375 watt-hours
• b.1.5 kilowatt-hours
• c.600 watt-hours
• d.6 kilowatt-hours✓

Energy equals power multiplied by time: 1,500 watts x 4 hours = 6,000 watt-hours, or 6 kilowatt-hours. The 1.5-kilowatt-hour answer reports only the power rating, and 375 watt-hours divides instead of multiplying.

A 40-ohm resistor and a 20-ohm resistor are connected in series across a 120-volt source. What is the voltage drop across the 40-ohm resistor?

• a.80 volts✓
• b.40 volts
• c.60 volts
• d.48 volts

In series the total resistance is 40 + 20 = 60 ohms, so the current is 120 / 60 = 2 amperes. The drop across the 40-ohm resistor is 2 x 40 = 80 volts, and the remaining 40 volts appears across the 20-ohm resistor, confirming the two drops sum to the source voltage.

Article 100 defines a qualified person as one who has which of the following?

• a.A journeyman license issued in any state
• b.Skills and knowledge related to the construction and operation of the electrical equipment and installations, plus safety training to recognize and avoid the hazards involved✓
• c.At least eight thousand hours of documented field experience working under the direct supervision of a licensed master electrician, regardless of whether any formal safety or hazard-recognition training has been completed
• d.A current first-aid and CPR certification

A qualified person is defined by demonstrated skills and knowledge related to the construction and operation of the equipment and installations, together with safety training to recognize and avoid the hazards involved. The definition is competency-based and does not hinge on a specific license, hour count or certificate.2023 NEC Art. 100

A continuous load draws 16 amperes. What is the minimum standard overcurrent device rating permitted?

• a.15 amperes
• b.16 amperes
• c.25 amperes
• d.20 amperes✓

An overcurrent device supplying a continuous load must be rated at not less than 125 percent of the load: 16 A x 1.25 = 20 A, a standard rating in NEC 240.6(A). See NEC 210.20(A).

A service uses 4/0 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor?

• a.4 AWG
• b.2 AWG✓
• c.1/0 AWG
• d.6 AWG

Table 250.66 places service conductors over 3/0 through 350 kcmil copper in the row requiring a 2 AWG copper grounding electrode conductor. The 4 AWG row is for 2/0 and 3/0, so reading one row low understates it. See NEC Table 250.66.

A box contains six 14 AWG conductors, one internal cable clamp and one duplex receptacle wired with 14 AWG. What minimum box volume is required?

• a.16.0 cubic inches
• b.12.0 cubic inches
• c.20.25 cubic inches
• d.18.0 cubic inches✓

Count six conductors, one allowance for all internal clamps, and two allowances for the device yoke = 9 allowances. Each 14 AWG allowance is 2.00 cubic inches: 9 x 2.00 = 18.0. See NEC 314.16(B).

A 20-horsepower, 460-volt, three-phase squirrel-cage motor has a table full-load current of 27 amperes. Using 75 degrees C copper terminations, what is the minimum branch-circuit conductor size?

• a.8 AWG
• b.12 AWG
• c.6 AWG
• d.10 AWG✓

Single-motor branch-circuit conductors must carry at least 125 percent of the table full-load current: 27 x 1.25 = 33.75 A. In the 75 degrees C column 12 AWG (25 A) fails and 10 AWG (35 A) qualifies. See NEC 430.22, Table 430.250 and Table 310.16.

A heating element of 10 ohms is connected across 120 volts. What current flows?

• a.1,200 amperes
• b.10 amperes
• c.12 amperes✓
• d.0.083 ampere

Ohm's law gives I = E / R = 120 / 10 = 12 amperes. Inverting the division gives the 0.083-ampere trap, and multiplying gives 1,200.

For a 16-ampere continuous load, what is the minimum copper branch-circuit conductor at 75 degrees C terminations using THWN?

• a.14 AWG
• b.10 AWG
• c.8 AWG
• d.12 AWG✓

The conductor must carry 125 percent of the continuous load = 20 A. In Table 310.16 (75 degrees C) 14 AWG copper is 20 A but the small-conductor rule NEC 240.4(D) limits 14 AWG to a 15 A device, so 12 AWG (25 A) is the minimum. See NEC 210.19(A).

A service is supplied by a single set of 400 kcmil copper ungrounded conductors. What is the minimum size copper grounding electrode conductor?

• a.2 AWG
• b.4 AWG
• c.1/0 AWG✓
• d.3/0 AWG

Service conductors over 350 through 600 kcmil copper require a 1/0 AWG copper grounding electrode conductor. The 2 AWG row applies to over 3/0 through 350 kcmil. See NEC Table 250.66.

A device box has two 12-2 nonmetallic-sheathed cables with equipment grounding conductors entering through internal clamps, and one single-pole switch (12 AWG). What minimum box volume is required?

• a.18.0 cubic inches✓
• b.16.0 cubic inches
• c.20.25 cubic inches
• d.15.75 cubic inches

Four insulated 12 AWG conductors, all grounding conductors as one, all clamps as one, and the switch yoke as two = 8 allowances. At 2.25 cubic inches each: 8 x 2.25 = 18.0. See NEC 314.16(B).

That 20-horsepower motor has a nameplate full-load current of 26 amperes and a marked service factor of 1.15. What is the maximum separate overload device rating?

• a.33.75 amperes
• b.29.9 amperes
• c.32.5 amperes✓
• d.26 amperes

Overload protection is based on nameplate current, and a service factor of 1.15 or greater permits 125 percent: 26 x 1.25 = 32.5 A. The 115 percent factor (29.9 A) applies only to lower-rated motors. See NEC 430.32(A)(1).

What power is consumed by a 240-volt resistive load drawing 15 amperes?

• a.16 watts
• b.3,000 watts
• c.255 watts
• d.3,600 watts✓

Power in a resistive single-phase circuit is P = E x I = 240 x 15 = 3,600 watts. Dividing gives 16 and adding gives 255.

Seven current-carrying 8 AWG THWN-2 copper conductors are installed in one raceway at a 30 degrees C ambient. What is the adjusted ampacity of each?

• a.44 amperes
• b.38.5 amperes✓
• c.33 amperes
• d.27.5 amperes

Begin at the 90 degrees C ampacity of 8 AWG copper, 55 A (Table 310.16), then apply the 70 percent adjustment for 7 through 9 current-carrying conductors: 55 x 0.70 = 38.5 A. See NEC 310.15(C)(1).

A service uses 1 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor?

• a.2 AWG
• b.6 AWG✓
• c.4 AWG
• d.8 AWG

Table 250.66 groups 1 and 1/0 AWG copper service conductors together and requires a 6 AWG copper grounding electrode conductor. The 8 AWG row is for 2 AWG and smaller. See NEC Table 250.66.

How many 12 AWG conductors may be installed in a 22.5-cubic-inch box with no clamps, devices or fittings?

• a.9
• b.10✓
• c.12
• d.11

Each 12 AWG conductor requires 2.25 cubic inches: 22.5 / 2.25 = 10 conductors exactly. See NEC 314.16(A) and (B).

For that 27-ampere three-phase motor, what is the maximum inverse-time circuit breaker for branch-circuit short-circuit and ground-fault protection, using the next standard size allowance?

• a.90 amperes
• b.70 amperes✓
• c.60 amperes
• d.80 amperes

An inverse-time breaker is permitted at 250 percent of full-load current: 27 x 2.50 = 67.5 A, which is not standard, so the next standard size of 70 A may be used. See Table 430.52(C)(1) and 430.52(C)(1) Exception 1.

How much power is dissipated when 6 amperes flows through a 25-ohm resistor?

• a.150 watts
• b.6.25 watts
• c.3,600 watts
• d.900 watts✓

Using P = I squared x R = 6 x 6 x 25 = 900 watts. Multiplying current by resistance without squaring gives 150 watts.

Five current-carrying 6 AWG THHN copper conductors run in a raceway through a 40 degrees C ambient. What is the adjusted ampacity of each?

• a.65 amperes
• b.48 amperes
• c.60 amperes
• d.54.6 amperes✓

The 90 degrees C ampacity of 6 AWG copper is 75 A. Apply the 36 to 40 degrees C correction of 0.91 and the 4 to 6 conductor adjustment of 0.80: 75 x 0.91 x 0.80 = 54.6 A. See NEC 310.15 and Table 310.16.

What is the minimum size copper equipment grounding conductor for a circuit protected at 100 amperes?

• a.8 AWG✓
• b.10 AWG
• c.6 AWG
• d.4 AWG

Table 250.122 is entered by the overcurrent device rating, and the 100-ampere row calls for 8 AWG copper. The 10 AWG row is 60 amperes and 6 AWG is 200 amperes. See NEC Table 250.122.

How many 14 AWG conductors may be installed in an 18.0-cubic-inch box with no clamps, devices or fittings?

• a.12
• b.10
• c.8
• d.9✓

Each 14 AWG conductor requires 2.00 cubic inches: 18.0 / 2.00 = 9 conductors. See NEC 314.16(A) and (B).

For the same 27-ampere motor, what is the maximum dual-element time-delay fuse at the standard 175 percent, using the next standard size allowance?

• a.40 amperes
• b.50 amperes✓
• c.60 amperes
• d.45 amperes

Dual-element time-delay fuses are permitted at 175 percent: 27 x 1.75 = 47.25 A, and the next standard size is 50 A. See Table 430.52(C)(1).

Three resistors of 5, 10 and 20 ohms are connected in series across 105 volts. What is the circuit current?

• a.0.33 ampere
• b.6 amperes
• c.30 amperes
• d.3 amperes✓

Series resistances add: 5 + 10 + 20 = 35 ohms, so I = 105 / 35 = 3 amperes.

A 120-volt single-phase circuit carries 16 amperes 150 feet on 10 AWG copper (10,380 circular mils). Using K = 12.9, what is the approximate voltage drop?

• a.3.0 volts
• b.12.0 volts
• c.6.0 volts✓
• d.9.0 volts

Single-phase VD = (2 x K x I x L) / CM = (2 x 12.9 x 16 x 150) / 10,380 = 61,920 / 10,380, about 6.0 V. Omitting the factor of 2 gives the 3.0-V trap. See NEC Chapter 9, Table 8.

What is the minimum size copper equipment grounding conductor for a 300-ampere feeder?

• a.2 AWG
• b.6 AWG
• c.3 AWG
• d.4 AWG✓

The 300-ampere row of Table 250.122 specifies 4 AWG copper. 6 AWG is 200 amperes and 3 AWG is 400 amperes, so those are adjacent rows. See NEC Table 250.122.

What is the minimum trade size of EMT required for sixteen 12 AWG THHN conductors?

• a.One-half inch
• b.One inch
• c.Three-quarter inch✓
• d.One and one-quarter inch

Annex C, Table C1 shows one-half-inch EMT holds nine 12 AWG THHN and three-quarter-inch EMT holds sixteen, so three-quarter inch is the minimum. See NEC Annex C, Table C1.

For the same 27-ampere motor, what is the maximum non-time-delay fuse at the standard 300 percent, using the next standard size allowance?

• a.110 amperes
• b.80 amperes
• c.90 amperes✓
• d.100 amperes

Non-time-delay fuses are permitted at 300 percent: 27 x 3.00 = 81 A, and the next standard size is 90 A. See Table 430.52(C)(1).

A 10-ohm resistor and a 40-ohm resistor are connected in parallel. What is the total resistance?

• a.4 ohms
• b.8 ohms✓
• c.25 ohms
• d.50 ohms

For two resistors in parallel, R = (R1 x R2) / (R1 + R2) = (10 x 40) / 50 = 400 / 50 = 8 ohms. Total parallel resistance is always less than the smallest branch.

A 480-volt three-phase feeder carries 30 amperes 300 feet on 4 AWG copper (41,740 circular mils). Using K = 12.9, what is the approximate voltage drop?

• a.4.8 volts✓
• b.9.6 volts
• c.5.6 volts
• d.2.8 volts

Three-phase VD = (1.732 x K x I x L) / CM = (1.732 x 12.9 x 30 x 300) / 41,740, about 4.8 V. Using 2 instead of 1.732 gives the 5.6-V answer. See NEC Chapter 9, Table 8.

What is the minimum size copper equipment grounding conductor for a 20-ampere branch circuit?

• a.14 AWG
• b.10 AWG
• c.8 AWG
• d.12 AWG✓

Table 250.122 lists 12 AWG copper at 20 amperes. 14 AWG is the 15-ampere value and 10 AWG is the 60-ampere value. See NEC Table 250.122.

When exactly one conductor is installed in a conduit or tubing, what is the maximum permitted fill percentage?

• a.40 percent
• b.31 percent
• c.53 percent✓
• d.60 percent

Chapter 9, Table 1 permits 53 percent fill for a single conductor, 31 percent for two, and 40 percent for three or more. See NEC Chapter 9, Table 1.

A 25-horsepower, 208-volt, three-phase squirrel-cage motor has a table full-load current of 74.8 amperes. Using 75 degrees C copper terminations, what is the minimum branch-circuit conductor size?

• a.6 AWG
• b.4 AWG
• c.2 AWG
• d.3 AWG✓

The conductor must carry 74.8 x 1.25 = 93.5 A. In the 75 degrees C column 4 AWG (85 A) fails and 3 AWG (100 A) qualifies. See NEC 430.22, Table 430.250 and Table 310.16.

Three 60-ohm resistors are connected in parallel. What is the total resistance?

• a.30 ohms
• b.180 ohms
• c.20 ohms✓
• d.60 ohms

For equal resistors in parallel, total resistance equals one value divided by the number of resistors: 60 / 3 = 20 ohms. Adding them gives the 180-ohm series answer.

A 240-volt circuit must carry 20 amperes 200 feet with voltage drop held to 3 percent. Using K = 12.9 for copper, what is the smallest conductor that meets the target?

• a.6 AWG
• b.10 AWG
• c.8 AWG✓
• d.12 AWG

Three percent of 240 V is 7.2 V, so required area = (2 x 12.9 x 20 x 200) / 7.2 = 103,200 / 7.2 = 14,333 circular mils. From Chapter 9, Table 8, 10 AWG (10,380 cmil) fails and 8 AWG (16,510 cmil) meets it. Voltage-drop sizing is advisory per the Informational Notes to NEC 210.19 and 215.2.

What is the minimum size copper equipment grounding conductor for a 500-ampere feeder?

• a.1 AWG
• b.4 AWG
• c.3 AWG
• d.2 AWG✓

The 500-ampere row of Table 250.122 requires 2 AWG copper. 3 AWG is 400 amperes and 1 AWG is 600 amperes. See NEC Table 250.122.

Four 250 kcmil THWN conductors, each 0.3970 square inch, are pulled into EMT. What is the minimum trade size?

• a.3 inch
• b.1 and 1/2 inch
• c.2 inch
• d.2 and 1/2 inch✓

Total area = 4 x 0.3970 = 1.588 square inches at 40 percent fill. Two-inch EMT allows about 1.342 square inches and fails; 2 and 1/2-inch EMT allows about 2.343 square inches and works. See NEC Chapter 9, Tables 1 and 4.

For that 74.8-ampere motor, what is the maximum inverse-time circuit breaker at 250 percent, using the next standard size allowance?

• a.150 amperes
• b.200 amperes✓
• c.225 amperes
• d.175 amperes

74.8 x 2.50 = 187 A, which is not standard, so the next standard size of 200 A may be used. See Table 430.52(C)(1).

A balanced three-phase load draws 30 amperes at 208 volts with a power factor of 0.90. What is the true power?

• a.Approximately 6.2 kilowatts
• b.Approximately 10.8 kilowatts
• c.Approximately 5.6 kilowatts
• d.Approximately 9.7 kilowatts✓

True power = 1.732 x E x I x PF = 1.732 x 208 x 30 x 0.90, about 9,730 watts. Omitting the power factor gives about 10.8 kVA of apparent power.

A feeder supplies 40 amperes of continuous load plus 60 amperes of noncontinuous load. What is the minimum standard overcurrent device rating?

• a.90 amperes
• b.125 amperes
• c.110 amperes✓
• d.100 amperes

The device is sized for the noncontinuous load plus 125 percent of the continuous load: 60 + (40 x 1.25) = 110 A, which is a standard rating. See NEC 215.3 and 240.6(A).

A ground ring encircling a building must be formed from at least 20 feet of bare copper conductor not smaller than what size?

• a.4 AWG
• b.6 AWG
• c.2 AWG✓
• d.1/0 AWG

A ground ring must encircle the building and consist of at least 20 feet of bare copper conductor not smaller than 2 AWG. See NEC 250.52(A)(4).

What is the maximum support spacing for a horizontal run of 1/2-inch trade size rigid metal conduit?

• a.10 feet✓
• b.6 feet
• c.5 feet
• d.12 feet

Rigid metal conduit of 1/2 and 3/4 inch is supported at intervals not exceeding 10 feet, and it must be secured within 3 feet of each termination. See NEC 344.30(B)(2).

A feeder supplies a 25-horsepower motor (34 amperes) and a 15-horsepower motor (21 amperes), both 460 volts three-phase. What minimum conductor ampacity is required?

• a.68.75 amperes
• b.48.75 amperes
• c.63.5 amperes✓
• d.55 amperes

Feeder conductors carry 125 percent of the largest motor plus the other full-load currents: (34 x 1.25) + 21 = 42.5 + 21 = 63.5 A. See NEC 430.24.

On a 208Y/120-volt wye system, what is the relationship between line current and phase current?

• a.Line current equals phase current divided by 1.732
• b.Line current equals 3 times phase current
• c.Line current equals 1.732 times phase current
• d.Line current equals phase current✓

In a wye configuration the line current equals the phase current, while the line voltage is 1.732 times the phase voltage. In a delta configuration those relationships reverse.

A 240-volt single-phase feeder supplies an 8-kilowatt continuous load. What is the minimum standard overcurrent device rating?

• a.45 amperes✓
• b.35 amperes
• c.50 amperes
• d.40 amperes

Load current = 8,000 / 240 = 33.3 A. Because the load is continuous, the device must be at least 33.3 x 1.25 = 41.7 A, so the next standard rating is 45 A. See NEC 210.20(A) and 240.6(A).

A plate electrode must present at least how much surface area to exterior soil?

• a.8 square feet
• b.4 square feet
• c.2 square feet✓
• d.1 square foot

A plate electrode of iron, steel or nonferrous metal must expose at least 2 square feet of surface to the surrounding earth. See NEC 250.52(A)(7).

What is the maximum support spacing for a 2-inch trade size rigid PVC conduit?

• a.6 feet
• b.3 feet
• c.5 feet✓
• d.8 feet

PVC support spacing depends on trade size: 1/2 through 1 inch every 3 feet, and 1 and 1/4 through 2 inch every 5 feet. See NEC 352.30(B).

For that two-motor feeder, if the largest branch-circuit protective device is 90 amperes, what is the maximum feeder overcurrent device rating?

• a.100 amperes
• b.111 amperes
• c.125 amperes
• d.110 amperes✓

The feeder device may not exceed the largest branch device plus the other motors' full-load currents: 90 + 21 = 111 A. Since 111 is not standard and this is a maximum, the next lower standard size of 110 A is used. See NEC 430.62(A).

A single-phase transformer has a 240-volt primary and a 48-volt secondary. If the secondary carries 50 amperes, what is the approximate primary current?

• a.5 amperes
• b.10 amperes✓
• c.50 amperes
• d.250 amperes

Voltage and current transform inversely and the volt-amperes match: 240 x I = 48 x 50, so I = 2,400 / 240 = 10 amperes. Inverting the ratio gives the 250-ampere trap.

Along a dwelling kitchen countertop, no point measured horizontally along the wall line may be more than what distance from a receptacle outlet?

• a.36 inches
• b.24 inches✓
• c.48 inches
• d.12 inches

No point along the kitchen counter wall line may be more than 24 inches from a receptacle, which places outlets no more than 48 inches apart. See NEC 210.52(C)(1).

When ungrounded conductors are increased in size for voltage drop, how must the equipment grounding conductor be adjusted?

• a.Doubled in every case
• b.Increased proportionally to the ungrounded conductors' increase in circular-mil area✓
• c.Sized only from Table 250.122 by the overcurrent device rating
• d.Left unchanged because the overcurrent device did not change

Where ungrounded conductors are upsized, the equipment grounding conductor must be increased proportionally by circular-mil area. See NEC 250.122(B).

A cable is run through a notch cut in the edge of a wood stud. What is required to protect it?

• a.A plastic bushing of any thickness
• b.A steel plate at least 1/8 inch thick
• c.A steel plate at least 1/16 inch thick installed across the notch✓
• d.No protection if the cable is stapled at the notch

Where a cable is laid in a notch, a steel plate, sleeve or clip at least 1/16 inch thick must protect it from screws and nails. See NEC 300.4(A)(2).

An air-conditioning condensing unit is marked minimum circuit ampacity 28.4 amperes. Using 75 degrees C copper, what is the minimum branch-circuit conductor size?

• a.8 AWG copper
• b.14 AWG copper
• c.10 AWG copper✓
• d.12 AWG copper

The minimum circuit ampacity sizes the conductors: 28.4 A calls for 10 AWG copper (35 A at 75 degrees C). See NEC 440.32 and 440.4(B).

What is the secondary full-load current of a 15 kVA single-phase transformer with a 240-volt secondary?

• a.62.5 amperes✓
• b.125 amperes
• c.31 amperes
• d.104 amperes

For a single-phase transformer, I = VA / E = 15,000 / 240 = 62.5 amperes.

A kitchen countertop or work surface must have a receptacle outlet if it is at least what width?

• a.12 inches✓
• b.18 inches
• c.6 inches
• d.24 inches

A countertop or work surface that is 12 inches or wider must be provided with at least one receptacle outlet. See NEC 210.52(C)(1).

A service is supplied by a single set of 350 kcmil copper ungrounded conductors. What is the minimum size copper main bonding jumper?

• a.3 AWG
• b.1/0 AWG
• c.2 AWG✓
• d.4 AWG

The main bonding jumper is sized from Table 250.102(C)(1), and 350 kcmil copper falls in the over 3/0 through 350 kcmil row requiring 2 AWG copper. See NEC 250.28(D)(1).

A pull box is used for a straight pull, and the largest raceway entering it is 4-inch trade size. What is the minimum length of the box in the direction of the pull?

• a.16 inches
• b.24 inches
• c.32 inches✓
• d.48 inches

For straight pulls the box length must be at least eight times the trade size of the largest raceway: 8 x 4 = 32 inches. See NEC 314.28(A)(1).

A hermetic refrigerant motor-compressor has a rated-load current of 22 amperes. What is the maximum branch-circuit short-circuit and ground-fault protective device at the standard 175 percent?

• a.45 amperes
• b.50 amperes
• c.40 amperes✓
• d.35 amperes

Protection is sized at not more than 175 percent of the rated-load current: 22 x 1.75 = 38.5 A, and the next standard size is 40 A. See NEC 440.22(A).

How much energy does a 2,000-watt load consume when operated continuously for 3 hours?

• a.666 watt-hours
• b.2 kilowatt-hours
• c.6 kilowatt-hours✓
• d.0.67 kilowatt-hour

Energy equals power multiplied by time: 2,000 watts x 3 hours = 6,000 watt-hours, or 6 kilowatt-hours.

At least one receptacle outlet must be installed within what distance of the outside edge of each dwelling bathroom basin?

• a.6 feet
• b.3 feet✓
• c.2 feet
• d.1 foot

A receptacle must be located within 3 feet of the outside edge of each basin, on a wall or partition adjacent to the basin or on the basin countertop. See NEC 210.52(D).

A service uses two parallel sets of 600 kcmil copper conductors per phase. Using the 12.5 percent rule, what is the minimum copper main bonding jumper?

• a.2/0 AWG
• b.4/0 AWG
• c.3/0 AWG✓
• d.250 kcmil

Where copper service conductors exceed 1,100 kcmil, the main bonding jumper must be at least 12.5 percent of that area: 2 x 600 = 1,200 kcmil, and 1,200 x 0.125 = 150 kcmil. 2/0 (133.1 kcmil) is too small; 3/0 (167.8 kcmil) qualifies. See NEC 250.28(D)(2).

An angle pull box has a 3-inch raceway and a 2-inch raceway entering the same wall with conductors turning 90 degrees. What is the minimum distance from that wall to the opposite wall?

• a.13 inches
• b.20 inches✓
• c.24 inches
• d.18 inches

For angle pulls the distance is six times the largest raceway plus the sum of the other raceway diameters on the same wall: (6 x 3) + 2 = 20 inches. See NEC 314.28(A)(2).

For that same 22-ampere rated-load compressor supplied alone, what minimum conductor ampacity is required?

• a.30 amperes
• b.22 amperes
• c.38.5 amperes
• d.27.5 amperes✓

Branch-circuit conductors for a single motor-compressor must be at least 125 percent of the rated-load or branch-circuit selection current: 22 x 1.25 = 27.5 A, which calls for 10 AWG copper. See NEC 440.32.

A 30-ohm resistor and a 60-ohm resistor are connected in series across a 90-volt source. What is the voltage drop across the 60-ohm resistor?

• a.60 volts✓
• b.30 volts
• c.90 volts
• d.45 volts

Total resistance is 30 + 60 = 90 ohms, so the current is 90 / 90 = 1 ampere. The drop across the 60-ohm resistor is 1 x 60 = 60 volts, and 30 volts appears across the 30-ohm resistor.

What is the minimum branch-circuit rating required for the dwelling laundry receptacle outlet(s)?

• a.15 amperes
• b.30 amperes
• c.20 amperes✓
• d.25 amperes

At least one 20-ampere branch circuit must supply the laundry receptacle outlet(s), and it may not serve other outlets. See NEC 210.11(C)(2) and 210.52(F).

A reinforcing bar used to form a concrete-encased electrode must be at least what diameter?

• a.1/4 inch
• b.5/8 inch
• c.3/8 inch
• d.1/2 inch✓

A concrete-encased electrode may use at least 20 feet of electrically conductive reinforcing bar not smaller than 1/2 inch in diameter, encased in at least 2 inches of concrete. See NEC 250.52(A)(3).

How must flexible metal conduit (FMC) be secured on a normal run?

• a.Within 12 inches of each box or fitting and at intervals not exceeding 4 and 1/2 feet✓
• b.Within 3 feet of each box and at intervals not exceeding 10 feet
• c.Within 12 inches of each box and at intervals not exceeding 6 feet
• d.Support is never required for FMC

FMC is secured within 12 inches of each box, cabinet or fitting and supported at intervals not exceeding 4 and 1/2 feet, with limited exceptions for flexibility. See NEC 348.30(A).

A recessed luminaire with a completely enclosed light source is installed in a clothes closet. What is the minimum clearance from the nearest point of the defined storage space?

• a.6 inches✓
• b.3 inches
• c.18 inches
• d.12 inches

A recessed luminaire with a completely enclosed light source may be as close as 6 inches to the storage space, while a surface-mounted enclosed luminaire requires 12 inches. See NEC 410.16(C)(2).

A 480-volt panelboard is mounted so there are no live or grounded parts opposite the working space. What is the minimum required depth of working space?

• a.3 feet✓
• b.3 and 1/2 feet
• c.2 and 1/2 feet
• d.4 feet

For 151 to 600 volts to ground, Condition 1 (no live or grounded parts opposite) requires 3 feet of depth. Condition 2 requires 3 and 1/2 feet and Condition 3 requires 4 feet. See NEC 110.26(A)(1).

Using the standard method, what is the general lighting load for a 2,500-square-foot dwelling before demand factors?

• a.5,625 volt-amperes
• b.11,250 volt-amperes
• c.7,500 volt-amperes✓
• d.6,000 volt-amperes

Dwelling general lighting is 3 volt-amperes per square foot: 2,500 x 3 = 7,500 VA. See NEC Table 220.12; verify the VA-per-square-foot value for the NEC edition your jurisdiction has adopted.

Where two rod electrodes are installed to form the grounding electrode system, what is the minimum spacing between them?

• a.6 feet✓
• b.8 feet
• c.3 feet
• d.10 feet

Supplementary rods must be at least 6 feet apart so their earth shells do not overlap. The 8-foot figure is the rod length, not the spacing. See NEC 250.53(A)(3).

What is the minimum burial cover for any wiring method installed directly beneath a public street, road or driveway?

• a.12 inches
• b.6 inches
• c.18 inches
• d.24 inches✓

Under streets, highways, roads, alleys, driveways and parking lots, all listed wiring methods require 24 inches of cover. See NEC Table 300.5(A).

A recessed luminaire not identified for insulation contact must be spaced at least what distance from combustible materials, other than at points of support?

• a.1 inch
• b.1/2 inch✓
• c.3 inches
• d.6 inches

A non-IC recessed luminaire must be at least 1/2 inch from combustible materials, other than at the points of support, and 3 inches from thermal insulation. See NEC 410.116(A)(1).

A 480-volt panelboard has exposed energized parts on both sides of the working space. What is the minimum required depth of working space?

• a.3 feet
• b.5 feet
• c.4 feet✓
• d.3 and 1/2 feet

For 151 to 600 volts to ground, Condition 3, with exposed live parts on both sides of the working space, requires a depth of 4 feet. See NEC 110.26(A)(1).

An apartment has the two required small-appliance branch circuits and no laundry circuit. What load must be included for the small-appliance circuits before demand factors?

• a.3,000 volt-amperes✓
• b.6,000 volt-amperes
• c.4,500 volt-amperes
• d.1,500 volt-amperes

Each small-appliance branch circuit is calculated at 1,500 VA: 2 x 1,500 = 3,000 VA. See NEC 220.52(A).

A single ground rod need not be supplemented by a second electrode if its resistance to earth does not exceed what value?

• a.25 ohms✓
• b.1 ohm
• c.5 ohms
• d.100 ohms

A single rod, pipe or plate electrode must be supplemented unless it is shown to have a resistance to earth of 25 ohms or less. See NEC 250.53(A)(2).

What is the smallest conductor size generally permitted for building branch-circuit wiring?

• a.18 AWG copper
• b.14 AWG copper✓
• c.16 AWG copper
• d.12 AWG copper

For general branch-circuit and building wiring the smallest conductor is 14 AWG copper; 18 and 16 AWG are permitted only for specific limited applications such as fixture wire and some Class 2 circuits. See NEC 310.106(A) and Table 310.16.

A generator nameplate current rating is 150 amperes. What minimum conductor size is required from the generator terminals to the first overcurrent device, using 75 degrees C copper?

• a.3/0 AWG
• b.2/0 AWG✓
• c.1 AWG
• d.1/0 AWG

Conductors from the generator terminals to the first device must be at least 115 percent of the nameplate current: 150 x 1.15 = 172.5 A. In the 75 degrees C column 1/0 (150 A) fails and 2/0 (175 A) qualifies. See NEC 445.13(A).

What is the minimum headroom of the working space about electrical equipment such as panelboards?

• a.6 and 1/2 feet✓
• b.3 feet
• c.7 feet
• d.6 feet

The minimum headroom of working space is 6 and 1/2 feet, or the height of the equipment if taller. See NEC 110.26(A)(3).

Using Column C of the household cooking-appliance demand table, what is the demand load for two 12-kilowatt household ranges on one feeder?

• a.11 kilowatts✓
• b.10 kilowatts
• c.8 kilowatts
• d.16 kilowatts

Column C of Table 220.55 gives 11 kilowatts for two household ranges rated not over 12 kilowatts each. See NEC 220.55.

A concrete-encased electrode using bare copper must be formed with at least 20 feet of what minimum conductor size?

• a.2 AWG
• b.4 AWG✓
• c.8 AWG
• d.6 AWG

A concrete-encased electrode may be at least 20 feet of bare copper not smaller than 4 AWG, or 20 feet of 1/2-inch or larger reinforcing bar, encased near the bottom of a footing. See NEC 250.52(A)(3).

At least one required 125-volt receptacle serving a permanently installed pool must be located within what distance range from the inside pool wall?

• a.Between 10 feet and 25 feet
• b.Between 6 feet and 20 feet✓
• c.Between 5 feet and 15 feet
• d.Between 3 feet and 10 feet

A general-use receptacle must be no closer than 6 feet, and at least one required receptacle must be located between 6 and 20 feet from the inside pool wall. See NEC 680.22(A).

A photovoltaic source circuit uses modules with a rated short-circuit current of 8 amperes. What minimum conductor ampacity is required before any adjustment factors?

• a.15.6 amperes
• b.12.5 amperes✓
• c.8 amperes
• d.10 amperes

The maximum circuit current is 125 percent of the rated short-circuit current: 8 x 1.25 = 10 A, and the conductor is then sized at 125 percent of that value: 10 x 1.25 = 12.5 A. See NEC 690.8(A) and (B).

Working spaces about service equipment, switchboards, panelboards or motor control centers installed indoors must be provided with what?

• a.A dedicated telephone
• b.Illumination✓
• c.A portable fire extinguisher
• d.A rubber grounding mat

Indoor working spaces about service equipment, switchboards, panelboards and motor control centers must have illumination. See NEC 110.26(D).

Using the standard demand table, what is the demand load for a single 16-kilowatt household electric range?

• a.8 kilowatts
• b.16 kilowatts
• c.9.6 kilowatts✓
• d.12 kilowatts

Column C for one range is 8 kilowatts. Note 1 increases that value 5 percent for each kilowatt over 12: 16 kW is 4 over, so 8 x 1.20 = 9.6 kilowatts. See NEC Table 220.55, Note 1.

Where rock bottom is encountered and an 8-foot rod cannot be driven vertically, at what maximum angle from vertical may the rod be driven?

• a.90 degrees
• b.45 degrees✓
• c.60 degrees
• d.30 degrees

If rock bottom prevents vertical driving, a rod electrode may be driven at an angle not exceeding 45 degrees from vertical, or buried in a trench at least 30 inches deep. See NEC 250.53(G).

A location where combustible dust is present in ignitible concentrations is classified as which type?

• a.Class IV
• b.Class II✓
• c.Class I
• d.Class III

Class II locations are those made hazardous by combustible dust. Class I covers flammable gases and vapors and Class III covers ignitible fibers and flyings. See NEC 500.5(C).

A continuous-duty motor with no marked service factor and no marked temperature rise will not start because the overload device selected at the basic percentage keeps tripping. To what maximum percentage of nameplate current may the overload device be increased?

• a.125 percent
• b.150 percent
• c.130 percent✓
• d.140 percent

Motors that do not have a service factor of 1.15 or greater or a marked temperature rise of 40 degrees C or less may be increased only to 130 percent, while better-rated motors may go to 140 percent. See NEC 430.32(C).

Under the Article 100 definitions, what does it mean to connect equipment to the earth?

• a.Grounding✓
• b.Insulating
• c.Bonding
• d.Derating

Grounding is the connection to earth or to a conductive body that extends the earth connection, while bonding is the connection of parts together for electrical continuity. See NEC Article 100.

A dwelling has a single household electric clothes dryer with a nameplate rating of 5.5 kilowatts. What value must be used for the dryer load?

• a.4,000 volt-amperes
• b.5,000 volt-amperes
• c.5,250 volt-amperes
• d.5,500 volt-amperes✓

The dryer load is 5,000 VA or the nameplate rating, whichever is larger: 5,500 exceeds 5,000, so 5,500 VA is used. See NEC 220.54.

A grounding electrode conductor connection to a ground rod buried in the earth must use what kind of fitting?

• a.A connector or clamp listed for direct burial in soil✓
• b.A tape-wrapped mechanical lug
• c.A solder joint
• d.Any indoor split-bolt connector

Connections to electrodes in contact with earth must be made with fittings listed and identified for direct soil or concrete burial as applicable. See NEC 250.70 and 250.68(A).

A 15-ampere, 125-volt receptacle is installed in a damp location such as under a roofed open porch. What cover is required?

• a.A cover that is weatherproof when no attachment plug is inserted✓
• b.A cover that is weatherproof whether or not a plug is inserted
• c.No cover is required in a damp location
• d.A standard indoor wall plate

In damp locations a receptacle needs an enclosure weatherproof when a plug is not inserted; the stricter in-use cover, weatherproof with a plug inserted, is required in wet locations. See NEC 406.9(A).

How many running overload protective devices are required for a single-phase, two-wire alternating-current motor?

• a.One✓
• b.Three
• c.Four
• d.Two

Table 430.37 requires one overload device in one ungrounded conductor for a single-phase, two-wire motor, whereas a three-phase motor requires one in each of the three phases. See NEC Table 430.37.

Article 100 defines a continuous load as one where the maximum current is expected to continue for how long?

• a.More than 24 hours
• b.Any duration over 100 amperes
• c.Only at night
• d.3 hours or more✓

A continuous load is one where the maximum current is expected to continue for 3 hours or more, which is why such loads are sized at 125 percent. See NEC Article 100.

A dwelling feeder supplies three fastened-in-place appliances other than ranges, dryers and heating or air-conditioning equipment. What demand factor may be applied to their nameplate total?

• a.65 percent
• b.75 percent
• c.100 percent✓
• d.50 percent

The 75 percent demand factor requires four or more such fastened-in-place appliances; with only three, no reduction is permitted. See NEC 220.53.

Under the current code, how must two to six service disconnects for a single service be arranged?

• a.Behind a single main breaker feeding sub-disconnects
• b.All mounted on a single removable panel
• c.Each in a separate enclosure, or in a listed assembly with individual enclosures, all grouped✓
• d.In any convenient locations throughout the building

The 2020 and 2023 codes require each of up to six service disconnects to be in a separate enclosure or a listed assembly with individual disconnect enclosures, grouped together. See NEC 230.71(B).

Receptacles installed outdoors in wet or damp locations must be which listed type?

• a.Twist-lock
• b.Weather-resistant✓
• c.Hospital-grade
• d.Isolated-ground

Fifteen- and 20-ampere, 125- and 250-volt receptacles in damp or wet locations must be listed weather-resistant. See NEC 406.9(A) and 406.9(B).

A 15-kVA, single-phase transformer has a 480-volt primary and is protected by primary overcurrent protection only at 125 percent. What is the maximum standard primary overcurrent device rating?

• a.35 amperes
• b.45 amperes
• c.40 amperes✓
• d.50 amperes

Primary full-load current = 15,000 / 480 = 31.25 A, and 31.25 x 1.25 = 39.06 A. The next standard rating is 40 A. See NEC 450.3(B).

What is the primary purpose of a lockout/tagout procedure?

• a.To improve the power factor of the circuit
• b.To increase the available fault current
• c.To reduce conductor voltage drop
• d.To prevent the unexpected energization or startup of equipment during servicing✓

Lockout/tagout keeps a disconnecting means in the open position so equipment cannot be unexpectedly energized or started while a worker is servicing it. This reflects OSHA 1910.147 and NFPA 70E safe-work practice.

Using the optional dwelling calculation, the general loads total 30 kVA. What is the demand load for these general loads?

• a.30 kVA
• b.22 kVA
• c.12 kVA
• d.18 kVA✓

The optional method takes the first 10 kVA at 100 percent and the remainder at 40 percent: 10 + (20 x 0.40) = 18 kVA. See NEC 220.82(B).

The point of attachment of overhead service-drop conductors to a building must be at least how far above finished grade?

• a.10 feet✓
• b.12 feet
• c.8 feet
• d.15 feet

The point of attachment of the service-drop or overhead service conductors must be at least 10 feet above finished grade and positioned to maintain the required conductor clearances. See NEC 230.26.

Which of the following is a recognized equipment grounding conductor?

• a.Electrical nonmetallic tubing
• b.Rigid metal conduit installed under its article✓
• c.A nonmetallic pull string
• d.Rigid PVC conduit

Metal raceways such as rigid metal conduit, intermediate metal conduit and EMT are recognized equipment grounding conductors; nonmetallic raceways are not. See NEC 250.118.

What is the maximum weight of a ceiling-suspended paddle fan that may be supported solely by a listed fan-rated outlet box without additional independent support?

• a.70 pounds✓
• b.50 pounds
• c.90 pounds
• d.35 pounds

A fan-listed outlet box may support a fan up to 70 pounds; a fan exceeding 70 pounds must be supported independently of the box. See NEC 314.27(C).

A Class A ground-fault circuit interrupter is designed to trip when the difference between the ungrounded and grounded conductor currents reaches approximately what value?

• a.100 milliamperes
• b.20 amperes
• c.4 to 6 milliamperes✓
• d.1 ampere

A Class A GFCI trips when the ground-fault (imbalance) current reaches 4 to 6 milliamperes, the level intended to protect people from electrocution, not to protect the circuit conductors.

A commercial building has 40 general-use receptacle outlets. Using the standard method, what receptacle load must be calculated before demand factors?

• a.6,000 volt-amperes
• b.4,800 volt-amperes
• c.7,200 volt-amperes✓
• d.7,920 volt-amperes

Non-dwelling receptacle outlets are calculated at 180 VA each: 40 x 180 = 7,200 VA. See NEC 220.14(I).

What is the minimum vertical clearance of overhead service conductors above a roof not readily accessible where the voltage does not exceed 300 volts to ground?

• a.8 feet✓
• b.10 feet
• c.12 feet
• d.3 feet

Overhead service conductors must maintain at least 8 feet of vertical clearance above the roof surface, over an area 3 feet in all directions from the roof edge, with reduced clearances only under specific listed conditions. See NEC 230.24(A).

Rigid PVC conduit requires an expansion fitting where the expected length change due to temperature is at least what value?

• a.1/8 inch
• b.1 inch
• c.1/2 inch
• d.1/4 inch✓

Expansion fittings are required for PVC conduit where the length change is expected to be 1/4 inch or more. See NEC 352.44.

A cord-and-plug-connected room air conditioner shares its branch circuit with lighting outlets. Its total marked rating must not exceed what percentage of the branch-circuit rating?

• a.100 percent
• b.80 percent
• c.50 percent✓
• d.125 percent

Where lighting units or other appliances are also supplied, a room air conditioner may not exceed 50 percent of the branch-circuit rating; if it is the only load, the limit is 80 percent. See NEC 440.62(B) and (C).

A retail store has 15 linear feet of show window. What show-window load must be included?

• a.1,800 volt-amperes
• b.1,500 volt-amperes
• c.2,700 volt-amperes
• d.3,000 volt-amperes✓

Show-window lighting is calculated at 200 VA per linear foot of show window: 15 x 200 = 3,000 VA. See NEC 220.14(G).

Overhead service conductors must maintain what minimum clearance from a window designed to be opened?

• a.6 feet
• b.3 feet✓
• c.5 feet
• d.10 feet

Service conductors must keep 3 feet of clearance from windows designed to open, doors, porches, decks, stairs and similar locations. Conductors above the top of a window are exempt. See NEC 230.9(A).

How many 12 AWG conductors may be installed in a 21.0-cubic-inch box with no clamps, devices or fittings?

• a.8
• b.10
• c.9✓
• d.11

Each 12 AWG conductor requires 2.25 cubic inches: 21.0 / 2.25 = 9.33, rounded down to 9 conductors. See NEC 314.16(A) and (B).

Capacitor circuit conductors must have an ampacity of at least what percentage of the rated current of the capacitor?

• a.135 percent✓
• b.150 percent
• c.125 percent
• d.115 percent

Conductors supplying a capacitor must be sized at not less than 135 percent of the rated current of the capacitor. See NEC 460.8(A).

A store lighting load of 20 amperes operates continuously. What is the minimum standard branch-circuit overcurrent device rating?

• a.20 amperes
• b.30 amperes
• c.35 amperes
• d.25 amperes✓

The device must be at least 125 percent of the continuous load: 20 x 1.25 = 25 A, which is a standard rating. See NEC 210.20(A).

What is the minimum clearance for overhead service conductors passing over a public street or road?

• a.15 feet
• b.12 feet
• c.10 feet
• d.18 feet✓

Overhead service conductors over public streets, roads, alleys and parking areas subject to truck traffic require 18 feet of clearance. See NEC 230.24(B).

What is the maximum permitted conductor fill of a metal wireway?

• a.31 percent
• b.53 percent
• c.20 percent✓
• d.40 percent

The conductors in a metal wireway may not fill more than 20 percent of its interior cross-sectional area. See NEC 376.22(A).

As defined in Article 100, what does 'in sight from' mean in terms of distance?

• a.Anywhere on the same floor level
• b.Visible and not more than 50 feet away✓
• c.Within 75 feet whether visible or not
• d.Visible and not more than 25 feet away

'In sight from' means the equipment is visible and not more than 50 feet distant from the other equipment. See NEC Article 100.

A feeder supplies 50 amperes of continuous load plus 40 amperes of noncontinuous load. Using 75 degrees C copper terminations, what is the minimum conductor size?

• a.1 AWG
• b.2 AWG✓
• c.3 AWG
• d.4 AWG

Required ampacity = noncontinuous + 125 percent continuous = 40 + (50 x 1.25) = 102.5 A. In the 75 degrees C column 3 AWG (100 A) fails and 2 AWG (115 A) qualifies. See NEC 215.2(A)(1) and Table 310.16.

Ground-fault protection of equipment is required for a solidly grounded wye service of more than 150 volts to ground when the disconnect is rated at least what value?

• a.1,000 amperes✓
• b.1,200 amperes
• c.600 amperes
• d.800 amperes

The threshold is a service disconnect rated 1,000 amperes or more on a solidly grounded wye system of more than 150 volts to ground but not over 1,000 volts phase-to-phase, such as 480Y/277. The 1,200-ampere figure is the maximum GFPE setting, not the trigger. See NEC 230.95.

A raceway enters a building underground from an outside source. What is required at the point of entry?

• a.It must be sealed or plugged to prevent moisture from entering the building✓
• b.It must be left open for ventilation
• c.It must be filled completely with concrete
• d.It must be bonded but is never sealed

Conduits and raceways entering a building underground must be sealed or plugged with an identified compound to stop moisture and gases from entering. See NEC 300.5(G).

A 40-horsepower, 460-volt, three-phase motor has a table full-load current of 52 amperes. What minimum ampere rating must the disconnecting means have?

• a.46 amperes
• b.65 amperes
• c.52 amperes
• d.59.8 amperes✓

The disconnecting means must be at least 115 percent of the full-load current: 52 x 1.15 = 59.8 A, so a 60-ampere or larger switch would be selected. See NEC 430.110(A).

Four current-carrying 10 AWG THHN copper conductors share one raceway at a 30 degrees C ambient. What is the adjusted ampacity of each before termination limits?

• a.28 amperes
• b.30 amperes
• c.32 amperes✓
• d.35 amperes

The 90 degrees C ampacity of 10 AWG copper is 40 A, and the 4 to 6 conductor adjustment is 80 percent: 40 x 0.80 = 32 A. The final overcurrent device is still limited to 30 A by NEC 240.4(D). See NEC 310.15(C)(1).

Neutral current that flows onto metal enclosures and grounding conductors because of an improper neutral-to-ground connection is known as what?

• a.Inductive reactance
• b.Fault current
• c.Displacement current
• d.Objectionable current✓

A neutral-to-ground bond made on the load side of the service creates parallel neutral paths, and the resulting current on grounding paths is objectionable current, which must be eliminated by correcting the connection. See NEC 250.6 and 250.142(B).

Type NM cable entering a single-gang nonmetallic box that has no cable clamps must be secured within what distance of the box?

• a.24 inches
• b.8 inches✓
• c.3 feet
• d.4 and 1/2 feet

Where a single-gang nonmetallic box without internal clamps is used, the NM cable must be secured within 8 inches of the box. See NEC 314.17(C) Exception and 334.30(A).

A 5-horsepower, 460-volt, three-phase motor has a table full-load current of 7.6 amperes. Using 75 degrees C copper, what is the minimum branch-circuit conductor size?

• a.16 AWG
• b.14 AWG✓
• c.12 AWG
• d.10 AWG

The conductor must carry 7.6 x 1.25 = 9.5 A. 14 AWG copper (20 A at 75 degrees C) is adequate; motor branch-circuit conductors are sized under Article 430 and are not restricted by the small-conductor rule of 240.4(D). See NEC 430.22.

A feeder neutral has a maximum unbalanced load of 250 amperes of non-nonlinear line-to-neutral load. Applying the permitted demand factor, what is the calculated neutral load?

• a.175 amperes
• b.250 amperes
• c.225 amperes
• d.235 amperes✓

For a feeder or service, the first 200 A of unbalanced neutral load is taken at 100 percent and the portion over 200 A at 70 percent: 200 + (50 x 0.70) = 235 A. See NEC 220.61(B).

On the load side of the service disconnecting means, may the grounded neutral conductor be used to ground equipment enclosures?

• a.Yes, where the neutral is 6 AWG copper or larger
• b.Yes, in any subpanel fed from the service equipment
• c.No; a separate equipment grounding conductor must be used✓
• d.Yes, but only in dwelling units

Downstream of the service disconnect the neutral and equipment grounding conductor must be kept separate so load current does not travel on enclosures and raceways. See NEC 250.142(B).

May a raceway be used as a means of support for another raceway or box?

• a.Yes, in all cases
• b.Yes, for spans under 6 feet
• c.Only where the raceway is nonmetallic
• d.No, except where the raceway is identified for that purpose or specifically permitted✓

Raceways may not be used to support other raceways, cables or nonelectrical equipment unless identified for the purpose or specifically permitted. See NEC 300.11(C).

A continuous-duty motor over 1 horsepower is marked with a temperature rise of 40 degrees C. What percentage of nameplate full-load current sets the maximum overload device?

• a.140 percent
• b.115 percent
• c.125 percent✓
• d.130 percent

A motor with a marked temperature rise not over 40 degrees C, like one with a service factor of 1.15 or greater, is permitted overload protection at 125 percent of nameplate current. See NEC 430.32(A)(1).

A branch circuit supplies a 44-ampere continuous load. What is the minimum standard overcurrent device rating?

• a.50 amperes
• b.55 amperes
• c.70 amperes
• d.60 amperes✓

44 x 1.25 = 55 A, which is not a standard rating, so the next standard size of 60 A must be used. See NEC 210.20(A) and 240.6(A).

A 30 kVA, three-phase transformer has a 480-volt primary and is protected by primary overcurrent protection only at 125 percent. What is the maximum standard primary overcurrent device rating?

• a.60 amperes
• b.50 amperes✓
• c.45 amperes
• d.40 amperes

Primary full-load current = 30,000 / (1.732 x 480) = 36.1 A, and 36.1 x 1.25 = 45.1 A. Because that exceeds the standard 45-ampere rating, the next standard size of 50 A is permitted. See NEC 450.3(B).

A junction box contains four 12 AWG and three 10 AWG conductors with no devices, clamps or fittings. What minimum box volume is required?

• a.16.5 cubic inches✓
• b.17.5 cubic inches
• c.14.0 cubic inches
• d.15.75 cubic inches

Each conductor is counted at the allowance for its own size: four 12 AWG at 2.25 = 9.0, and three 10 AWG at 2.50 = 7.5, for 16.5 cubic inches. See NEC 314.16(B)(1).

A feeder supplies a 30-horsepower motor (40 amperes), a 20-horsepower motor (27 amperes) and a 10-horsepower motor (14 amperes), all 460 volts three-phase. What minimum conductor ampacity is required?

• a.91 amperes✓
• b.101.25 amperes
• c.81 amperes
• d.95 amperes

Feeder ampacity = 125 percent of the largest motor plus the sum of the others: (40 x 1.25) + 27 + 14 = 50 + 41 = 91 A. See NEC 430.24.

A 120-volt branch circuit shows a measured voltage drop of 4.8 volts. What is the percentage voltage drop?

• a.4 percent✓
• b.5 percent
• c.3 percent
• d.2 percent

Percentage voltage drop = 4.8 / 120 = 0.04, or 4 percent, which exceeds the 3 percent branch-circuit guideline. See the Informational Note to NEC 210.19.

What is the secondary full-load current of a 112.5 kVA transformer with a 208Y/120-volt three-phase secondary?

• a.541 amperes
• b.312 amperes✓
• c.270 amperes
• d.156 amperes

Secondary current = VA / (1.732 x E) = 112,500 / (1.732 x 208) = 112,500 / 360.3, about 312 amperes. Dividing by voltage alone gives the 541-ampere trap.

What is the minimum trade size of EMT required for six 10 AWG THHN conductors?

• a.One inch
• b.Three-quarter inch✓
• c.One-half inch
• d.One and one-quarter inch

Annex C, Table C1 shows one-half-inch EMT holds five 10 AWG THHN and three-quarter-inch EMT holds ten, so three-quarter inch is the minimum for six. See NEC Annex C, Table C1.

A single receptacle is installed on an individual 20-ampere branch circuit. What is the minimum ampere rating of that receptacle?

• a.20 amperes✓
• b.30 amperes
• c.25 amperes
• d.15 amperes

A single receptacle on an individual branch circuit must have an ampere rating not less than the branch-circuit rating: 20 A. See NEC 210.21(B)(1).

How is the bonding jumper for exposed structural metal building framing sized?

• a.From Table 250.66, based on the ungrounded service conductor size✓
• b.Always 6 AWG copper regardless of service size
• c.From Table 310.16, by the service ampacity
• d.From Table 250.122, by the overcurrent device rating

The bonding jumper for exposed structural metal that is likely to become energized is sized from Table 250.66 using the ungrounded service-entrance conductors. See NEC 250.104(C).

A metal outlet box is supplied by a wiring method that includes an equipment grounding conductor. How must the box be treated?

• a.It must be left isolated from ground
• b.It must be connected to the grounded neutral bar
• c.It must be connected to the equipment grounding conductor✓
• d.It need be bonded only in a wet location

A metal box must be connected to an equipment grounding conductor so it is bonded and any fault will clear. See NEC 250.148 and 314.4.

What is the maximum continuous load permitted on a 15-ampere branch circuit?

• a.18 amperes
• b.12 amperes✓
• c.15 amperes
• d.10 amperes

A continuous load may not exceed 80 percent of the overcurrent device rating: 15 x 0.80 = 12 A. See NEC 210.20(A).

For a separately derived system, the grounding electrode conductor connects to the grounded conductor at the same point where what is installed?

• a.The largest branch-circuit overcurrent device
• b.The main bonding jumper at the service
• c.The system bonding jumper✓
• d.Every downstream equipment grounding bus

The grounding electrode conductor for a separately derived system connects the grounded conductor to the electrode at the same single point where the system bonding jumper is installed. See NEC 250.30(A).

An insulated bushing or fitting to protect conductors from abrasion is required where conductors of what size or larger enter a raceway or enclosure?

• a.1 AWG
• b.4 AWG✓
• c.8 AWG
• d.6 AWG

Where ungrounded conductors of 4 AWG or larger enter a raceway in a cabinet, box or enclosure, a fitting providing a smoothly rounded insulating surface, such as an insulating bushing, is required. See NEC 300.4(G).

A dwelling has a combined general lighting, small-appliance and laundry load of 8,000 volt-amperes. Applying the standard demand factors, what is the demand load?

• a.4,750 volt-amperes✓
• b.8,000 volt-amperes
• c.2,800 volt-amperes
• d.5,000 volt-amperes

The dwelling lighting demand table takes the first 3,000 VA at 100 percent and the remainder at 35 percent: 3,000 + (5,000 x 0.35) = 4,750 VA. See NEC Table 220.45 (renumbered from Table 220.42 in the 2023 NEC).

A supply-side bonding jumper on the line side of the service is sized from which table?

• a.Table 220.55
• b.Table 250.102(C)(1)✓
• c.Table 310.16
• d.Table 250.122

Supply-side bonding jumpers are sized from Table 250.102(C)(1), based on the ungrounded supply conductors, not from the equipment grounding conductor table. See NEC 250.102(C).

In box-fill calculations, how is a device yoke or strap counted?

• a.As two conductor volume allowances, based on the largest conductor connected to the device✓
• b.It is not counted at all
• c.As one conductor volume allowance
• d.As two allowances, based on the smallest conductor

Each yoke or strap containing a device or utilization equipment is counted as two conductor volume allowances based on the largest conductor connected to it. See NEC 314.16(B)(4).

In a dwelling-unit load calculation, how are the general-use 15- and 20-ampere receptacle outlets handled?

• a.They are calculated at 180 volt-amperes each in addition to the lighting load
• b.They are omitted from the load calculation entirely
• c.They are calculated at 1.5 amperes each
• d.They are included in the general lighting volt-amperes and are not calculated separately✓

In dwelling units, general-use receptacle outlets and lighting outlets are considered part of the general lighting load at 3 VA per square foot and no additional volt-amperes are added for them. See NEC 220.14(J).

An equipment grounding conductor of the wire type is never required to be larger than what?

• a.The circuit conductors supplying the equipment✓
• b.Twice the value shown in Table 250.122
• c.6 AWG copper in all cases
• d.The ungrounded service conductor size in every case

An equipment grounding conductor need not be larger than the circuit conductors supplying the equipment. See NEC 250.122(A).

A branch circuit supplies a 32-ampere continuous load. Using 75 degrees C copper terminations, what is the minimum conductor size?

• a.6 AWG
• b.10 AWG
• c.12 AWG
• d.8 AWG✓

The conductor must carry at least 125 percent of the continuous load: 32 x 1.25 = 40 A. In the 75 degrees C column 10 AWG (35 A) fails and 8 AWG (50 A) qualifies. See NEC 210.19(A) and Table 310.16.

What is the rule for a bare aluminum grounding electrode conductor near the earth?

• a.It must be installed within 18 inches of the earth
• b.It may not be used in direct contact with earth or masonry, or within 18 inches of the earth✓
• c.It may be buried directly in the earth like copper
• d.Aluminum grounding electrode conductors are prohibited entirely

Bare or exposed aluminum grounding electrode conductors may not be used in direct contact with masonry or earth or where subject to corrosive conditions, and may not be terminated within 18 inches of the earth. See NEC 250.64(A).

Which dwelling-unit location requires arc-fault circuit-interrupter protection for 120-volt, 15- and 20-ampere branch circuits?

• a.A bathroom
• b.A bedroom✓
• c.An unfinished basement
• d.An outdoor receptacle

AFCI protection covers most habitable dwelling areas, including bedrooms, kitchens, living rooms and laundry areas. Bathrooms, unfinished basements and outdoor receptacles are addressed by GFCI rather than AFCI requirements. See NEC 210.12(A).

How must the multiple grounding electrodes present at a building be arranged?

• a.Electrodes must be at least 100 feet apart
• b.A ground rod may never be combined with a water pipe electrode
• c.All electrodes present must be bonded together to form the grounding electrode system✓
• d.Only one electrode is permitted per building

All grounding electrodes that are present, such as a water pipe, concrete-encased electrode and ground rods, must be bonded together to form the grounding electrode system. See NEC 250.50.

Which dwelling-unit location requires GFCI protection for 125-volt, 15- and 20-ampere receptacles?

• a.A living-room wall receptacle
• b.A bedroom receptacle
• c.A hallway receptacle
• d.A garage✓

NEC 210.8(A) lists garages among the GFCI areas along with bathrooms, kitchens, laundry areas, basements, crawl spaces and outdoors. Living rooms, bedrooms and hallways are AFCI areas instead.

A feeder supplies a 60-ampere continuous load. What is the minimum standard overcurrent device rating?

• a.70 amperes
• b.75 amperes
• c.80 amperes✓
• d.90 amperes

60 x 1.25 = 75 A, which is not a standard rating, so the next standard size of 80 A must be used. See NEC 215.3 and 240.6(A).

An electric-vehicle supply equipment branch circuit serves a 40-ampere EV charging load. What minimum overcurrent device and conductor ampacity are required?

• a.50 amperes✓
• b.45 amperes
• c.60 amperes
• d.40 amperes

Electric-vehicle charging load is treated as continuous, so the overcurrent device and conductors are sized at 125 percent: 40 x 1.25 = 50 A. See NEC 625.41 and 625.42.

A dwelling has a combined general lighting, small-appliance and laundry load of 3,600 volt-amperes. Applying the standard demand factors, what is the demand load?

• a.3,600 volt-amperes
• b.3,150 volt-amperes
• c.3,210 volt-amperes✓
• d.1,260 volt-amperes

The first 3,000 VA is taken at 100 percent and the remainder at 35 percent: 3,000 + (600 x 0.35) = 3,210 VA. See NEC Table 220.45.