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

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

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).

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).

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).

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.

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.

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.

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.

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 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).

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).

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).

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).

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).

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.

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).

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.

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.

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 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.

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).

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).

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).

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).

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.

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).

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).

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 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.

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).

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).

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).

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).

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.

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).

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.