CSLB General Building (B) — 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 gas piping system as the supplement
• 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 only if the resistance to earth is 25 ohms or less

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 if the neutral is at least 6 AWG copper
• c.It is permitted in any panelboard fed from the service
• 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 the box and supported every 6 feet
• 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 the box and supported every 6 feet

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 rerouted through a notch instead
• 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, provided the cable is Type MC

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 controller only, with no rule about the motor

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.To the structural ceiling in all cases
• b.3 feet above the equipment in all cases
• 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.