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20 questions · 2023 NEC · Answers and explanations included

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Tap an answer to check it. Each question shows the correct answer, why it's right and the NEC section to look up. These are the same 20 questions the Journeyman Electrician Exam AI app gives you free, covering 12 exam topics.

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Question 1 · Electrical theoryA 120-volt circuit supplies a resistive load of 24 ohms. How much current flows?
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Answer: D. 5 A.

Ohm's law says current equals voltage divided by resistance. 120 V divided by 24 ohms gives 5 A.

  1. I = E / R
  2. I = 120 V / 24 Ω
  3. I = 5 A
Question 2 · Electrical theoryA current of 12 amperes flows through a 10-ohm resistor. What is the voltage across the resistor?
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Answer: C. 120 V.

Voltage equals current times resistance. 12 A times 10 ohms equals 120 V.

  1. E = I × R
  2. E = 12 A × 10 Ω
  3. E = 120 V
Question 3 · Overcurrent protectionUnless specifically permitted elsewhere in the NEC, what is the maximum overcurrent protection allowed for 14 AWG copper conductors?
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Answer: D. 15 A. NEC 240.4(D)

The small-conductor rule caps 14 AWG copper at 15 A regardless of its table ampacity. This limit applies after any correction and adjustment factors are considered.

Question 4 · Overcurrent protectionWhat is the maximum overcurrent device rating generally permitted for 12 AWG copper branch-circuit conductors?
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Answer: C. 20 A. NEC 240.4(D)

The small-conductor rule limits 12 AWG copper to 20 A protection even though its 75°C and 90°C table values are higher. Specific exceptions exist, such as motor and air-conditioning circuits.

Question 5 · Grounding and bondingA service has 3/0 AWG copper ungrounded service-entrance conductors. What is the minimum size copper grounding electrode conductor to a metal underground water pipe?
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Answer: D. 4 AWG. NEC Table 250.66

GEC size is based on the largest ungrounded service conductor (or equivalent area of parallel sets). For 2/0 or 3/0 copper, Table 250.66 requires a 4 AWG copper GEC.

  1. Largest ungrounded service conductor = 3/0 Cu
  2. Table 250.66 row: 2/0 or 3/0 Cu
  3. GEC = 4 AWG Cu
Question 6 · Grounding and bondingA 200 A service uses 250 kcmil copper service-entrance conductors. What size copper GEC is required to the building's structural steel electrode?
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Answer: C. 2 AWG. NEC Table 250.66

250 kcmil copper falls in the over 3/0 through 350 kcmil row of Table 250.66, which calls for a 2 AWG copper GEC. Note that the service rating is not used; the conductor size is.

  1. Service conductor = 250 kcmil Cu
  2. Table 250.66 row: over 3/0 through 350 kcmil
  3. GEC = 2 AWG Cu
Question 7 · Branch circuitsUnder the 2023 NEC, a 125-volt, 15-ampere receptacle installed behind the refrigerator in a dwelling-unit kitchen, not serving the countertop, must have what protection?
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Answer: D. GFCI protection. NEC 210.8(A)

The 2023 NEC lists kitchens without limiting the rule to countertop receptacles, so all 125-volt through 250-volt kitchen receptacles on circuits 150 volts or less to ground need GFCI protection. Older editions limited this to countertop receptacles.

Question 8 · Branch circuitsA 125-volt, 20-ampere receptacle is installed in a finished basement recreation room of a dwelling. Is GFCI protection required?
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Answer: C. Yes, all basement receptacles in dwelling units require GFCI protection. NEC 210.8(A)

Dwelling-unit GFCI requirements apply to basements whether finished or unfinished. This change was made because basements are often damp and have concrete floors.

Question 9 · Services and feedersOverhead service conductors pass over a flat roof that is not subject to pedestrian traffic. What is the general minimum vertical clearance above the roof surface?
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Answer: D. 8 ft 6 in. NEC 230.24(A)

The general rule requires 8 ft 6 in of vertical clearance above a roof. Reduced clearances are allowed only under specific exceptions, such as steep roofs or short overhang runs at 300 volts or less.

Question 10 · Services and feedersOverhead service conductors operating at 120/240 volts pass over a roof with a slope of 6 in 12. What is the minimum vertical clearance above the roof?
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Answer: C. 3 ft. NEC 230.24(A)

Where the voltage between conductors does not exceed 300 volts and the roof slope is at least 4 in 12, the clearance may be reduced to 3 ft. A steep roof is unlikely to have people walking on it.

  1. Voltage between conductors ≤ 300 V
  2. Roof slope 6/12 is at least 4/12 → 230.24(A) Exception 2
  3. Minimum clearance = 3 ft
Question 11 · Conductor ampacityWhat is the ampacity of 8 AWG THWN copper from the 75°C column of Table 310.16, with not more than three current-carrying conductors at 30°C ambient?
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Answer: D. 50 A. NEC Table 310.16

Table 310.16 lists 8 AWG copper at 40 A (60°C), 50 A (75°C), and 55 A (90°C). THWN is a 75°C insulation, so 50 A applies.

  1. THWN is a 75°C insulation
  2. Table 310.16, copper, 8 AWG, 75°C column
  3. Ampacity = 50 A
Question 12 · Conductor ampacityWhat is the 90°C table ampacity of 6 AWG THHN copper?
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Answer: C. 75 A. NEC Table 310.16

THHN is rated 90°C in dry and damp locations. Table 310.16 lists 6 AWG copper at 75 A in the 90°C column. This value is mainly used as a starting point for derating.

  1. THHN is a 90°C insulation
  2. Table 310.16, copper, 6 AWG, 90°C column
  3. Ampacity = 75 A
Question 13 · Wiring methodsType NM cable run along studs must be secured within what distance of each box and at what maximum interval?
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Answer: D. Within 12 in of each box, and at intervals not exceeding 4-1/2 ft. NEC 334.30

NM cable must be stapled or otherwise secured within 12 in of every box, cabinet, or fitting and at least every 4-1/2 ft. Cable run through bored holes at those intervals is considered supported.

Question 14 · Wiring methodsNM cable entering a single-gang nonmetallic box (about 2-1/4 × 4 in) without a cable clamp must be secured within what distance of the box?
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Answer: C. 8 in. NEC 314.17

Small single-gang nonmetallic boxes may be used without cable clamps when the cable is fastened within 8 in of the box. The sheath must also extend at least 1/4 in into the box.

  1. Single-gang nonmetallic box, no cable clamp
  2. 314.17 securing distance for this exception
  3. Within 8 in of the box
Question 15 · Box and conduit fillFor box fill calculations, what volume allowance is required for each 14 AWG conductor?
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Answer: D. 2.00 cubic in. NEC Table 314.16(B)(1)

Table 314.16(B) assigns a volume to each conductor size. 14 AWG requires 2.00 cubic inches per counted conductor.

Question 16 · Load calculationsA one-family dwelling has 2,400 sq ft of livable floor area. What is the general lighting load before demand factors?
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Answer: D. 7,200 VA. NEC 220.41

Dwelling units use a minimum unit load of 3 VA per sq ft. 2,400 × 3 = 7,200 VA, which also covers the general-use receptacles.

  1. Unit load = 3 VA/ft²
  2. 2,400 ft² × 3 VA
  3. = 7,200 VA
Question 17 · Load calculationsUnder the 2023 NEC standard method, which area is excluded when calculating the general lighting floor area of a dwelling?
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Answer: C. An open porch. NEC 220.5(C); 220.41

The 2023 standard-method floor area is based on outside dimensions and includes the garage. It excludes open porches and unfinished areas not adaptable for future use as a habitable room or occupiable space. The dwelling optional method in 220.82 has its own floor-area language.

Question 18 · Motors and controlsWhen sizing branch-circuit conductors and short-circuit/ground-fault protection for a general-purpose AC motor, which current value must be used?
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Answer: D. The full-load current from Tables 430.247 through 430.250. NEC 430.6(A)(1)

Conductor ampacity and short-circuit protection are based on the table values, not the nameplate. This keeps the installation adequate if the motor is later replaced with a different one of the same horsepower.

Question 19 · TransformersWhat is the full-load secondary current of a 50 kVA, single-phase transformer with a 240-volt secondary?
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Answer: D. 208 A.

Single-phase current equals VA divided by voltage. 50,000 ÷ 240 ≈ 208 A.

  1. I = VA / E
  2. I = 50,000 / 240
  3. I ≈ 208 A
Question 20 · Special locationsWhat is the minimum distance from the inside wall of a permanently installed pool to a 125-volt, 15- or 20-ampere receptacle?
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Answer: D. 6 ft. NEC 680.22(A)

Receptacles must be at least 6 ft from the inside walls of a pool, measured along the shortest path a cord would follow. Receptacles closer than that invite cord-connected appliances near the water.

  1. Receptacle near a permanently installed pool
  2. 680.22(A): measured along the shortest cord path
  3. Minimum = 6 ft

Answer key

For printing or checking your work. Most journeyman exams need 70% to 75% to pass, so aim for at least 15 of 20.

#TopicAnswerNEC
1Electrical theoryD. 5 A
2Electrical theoryC. 120 V
3Overcurrent protectionD. 15 A240.4(D)
4Overcurrent protectionC. 20 A240.4(D)
5Grounding and bondingD. 4 AWGTable 250.66
6Grounding and bondingC. 2 AWGTable 250.66
7Branch circuitsD. GFCI protection210.8(A)
8Branch circuitsC. Yes, all basement receptacles in dwelling units require GFCI protection210.8(A)
9Services and feedersD. 8 ft 6 in230.24(A)
10Services and feedersC. 3 ft230.24(A)
11Conductor ampacityD. 50 ATable 310.16
12Conductor ampacityC. 75 ATable 310.16
13Wiring methodsD. Within 12 in of each box, and at intervals not exceeding 4-1/2 ft334.30
14Wiring methodsC. 8 in314.17
15Box and conduit fillD. 2.00 cubic inTable 314.16(B)(1)
16Load calculationsD. 7,200 VA220.41
17Load calculationsC. An open porch220.5(C); 220.41
18Motors and controlsD. The full-load current from Tables 430.247 through 430.250430.6(A)(1)
19TransformersD. 208 A
20Special locationsD. 6 ft680.22(A)

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