Electrician Practice Questions (NEC)
These questions are written for anyone preparing for a state journeyman or master electrician licensing exam. Most of those exams are open book and built around the National Electrical Code, so the questions here follow the NEC (2023 edition, using values that have been stable across recent editions) and add the basic electrical theory the exams also test.
The pool covers conductor ampacity and derating, overcurrent protection, grounding and bonding, box and conduit fill, dwelling circuit requirements and theory calculations. Take the 10-question timed quiz as often as you like; each answer comes with the reasoning and the NEC article behind it, so a wrong answer teaches as much as a right one.
Question of the day
Grounding and bonding · October 8
A single 8-foot ground rod at a new dwelling service measures 40 ohms to earth. What does the NEC require?
NEC 250.53(A)(2) requires a single rod, pipe or plate electrode to be supplemented by another electrode unless it tests at 25 ohms or less, and 250.53(B) requires rod electrodes to be at least 6 feet apart. Once the second electrode is installed, no particular resistance has to be reached.
Show the answer
D. Add a second electrode at least 6 feet away — NEC 250.53(A)(2) requires a single rod, pipe or plate electrode to be supplemented by another electrode unless it tests at 25 ohms or less, and 250.53(B) requires rod electrodes to be at least 6 feet apart. Once the second electrode is installed, no particular resistance has to be reached.
10-question sample
Ten of the 15 sample questions, at random, one at a time, with the explanation after each answer. About five minutes. Full-length timed mock exams are in VoltPrep Electrician Exam Prep.
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VoltPrep Electrician Exam Prep
NICET/Tools1,000 practice questions for the journeyman and master electrician exams, with the code-based reasoning behind each answer.
Voltbox: Electrician Toolbox
NICET/ToolsWire, breaker and conduit calculators plus a full multimeter guide, all offline, so they work in a basement or a mechanical room with no signal.
How to study for the Electrician (NEC) exam
- Learn the layout of the NEC (chapters, articles and the index) so you can find any section in under a minute; most state exams are open book, and time is what runs out.
- Memorize the 240.4(D) small-conductor limits and the Table 310.16 copper values from 14 AWG through 1/0 so routine sizing questions take seconds instead of a table lookup.
- Work derating in a fixed order: start from the insulation column, apply the ambient correction and the conductor-count adjustment, then check the result against the 75°C termination limit.
- For box fill, list every item in 314.16(B) on paper before multiplying; most mistakes come from miscounting equipment grounding conductors and device yokes.
- Write the formula first on theory problems (E = I × R, P = E × I, √3 for three-phase) and carry the units through, which catches most arithmetic slips.
All 15 questions with answers
Open a question to see the answer and the reasoning. Topics: Conductor ampacity, Overcurrent protection, Grounding and bonding, Box and conduit fill, Dwelling circuits, Electrical theory.
1. Nine current-carrying 10 AWG THHN copper conductors run together in one conduit. Starting from the 90°C ampacity of 40 amperes, what is the adjusted ampacity?
- 40 amperes
- 32 amperes
- 28 amperes
- 20 amperes
Answer: C. NEC 310.15(C)(1) adjusts for more than three current-carrying conductors: 4 to 6 conductors 80%, 7 to 9 conductors 70%, 10 to 20 conductors 50%. Nine conductors means 40 × 0.70 = 28 amperes. The 32-ampere answer applies the 80% factor that belongs to 4 to 6 conductors.
Topic: Conductor ampacity
2. An 8 AWG THHN copper conductor (90°C ampacity 55 amperes) terminates on a circuit breaker whose terminals are rated 75°C. What ampacity may be used at that termination?
- 40 amperes
- 50 amperes
- 55 amperes
- 65 amperes
Answer: B. NEC 110.14(C) limits the ampacity at a termination to the column matching the terminal rating, so the 75°C value of 50 amperes governs for 8 AWG copper. The 90°C value of 55 amperes may only be used as the starting point for adjustment and correction; 40 amperes is the 60°C value.
Topic: Conductor ampacity
3. A branch circuit supplies a continuous load of 32 amperes. Before any adjustment or correction factors, what minimum conductor ampacity is required?
- 26 amperes
- 32 amperes
- 36 amperes
- 40 amperes
Answer: D. NEC 210.19(A)(1) sizes branch-circuit conductors for 100% of the noncontinuous load plus 125% of the continuous load, so 32 × 1.25 = 40 amperes, and 210.20(A) sizes the overcurrent device the same way. Applying 80% (26 amperes) runs the rule backward; 80% is simply the inverse view of the same 125% requirement.
Topic: Conductor ampacity
4. Unless another NEC section specifically permits otherwise, what is the maximum overcurrent device rating for 10 AWG copper conductors?
- 20 amperes
- 25 amperes
- 30 amperes
- 35 amperes
Answer: C. NEC 240.4(D) caps small conductors at 15 amperes for 14 AWG, 20 amperes for 12 AWG and 30 amperes for 10 AWG copper. The 35-ampere figure is the 75°C ampacity in Table 310.16, which the small-conductor rule overrides except for specific cases such as motor circuits listed in 240.4(E) and (G).
Topic: Overcurrent protection
5. Feeder conductors to a panelboard have an ampacity of 92 amperes after adjustment. What is the largest standard breaker that may protect them?
- 80 amperes
- 90 amperes
- 100 amperes
- 110 amperes
Answer: C. NEC 240.4(B) allows the next higher standard rating from 240.6(A) when the conductor ampacity does not match a standard size, the device is rated 800 amperes or less, and the conductors do not supply a multioutlet branch circuit for cord-and-plug loads. The next standard size above 92 amperes is 100; 90 amperes would be the answer only if rounding down were required.
Topic: Overcurrent protection
6. What is the main job of the equipment grounding conductor in a branch circuit?
- Carry normal load current back to the source
- Lower the voltage between the neutral and earth
- Dissipate lightning energy into the earth
- Give fault current a low-impedance path so the breaker opens
Answer: D. NEC 250.4(A)(5) requires an effective ground-fault current path with low impedance so enough current flows to open the overcurrent device quickly, and it states that the earth is not an effective ground-fault current path. Normal load current returns on the grounded (neutral) conductor, never on the equipment grounding conductor.
Topic: Grounding and bonding
7. A feeder supplies a subpanel in the same building as the service. How should the electrician treat the neutral in that subpanel?
- Isolate the neutral bar; land grounds on a bonded ground bar
- Install the bonding screw so neutrals and grounds share the enclosure
- Land neutrals and equipment grounds on the same bar
- Omit the feeder ground; the grounded neutral is enough
Answer: A. NEC 250.24(A)(5) prohibits reconnecting the grounded conductor to the equipment grounding conductor or the enclosure on the load side of the service disconnect, so the neutral-to-ground bond exists only at the service (the main bonding jumper). Bonding the neutral again in the subpanel would put neutral current on the equipment grounding conductor and metal parts.
Topic: Grounding and bonding
8. A single 8-foot ground rod at a new dwelling service measures 40 ohms to earth. What does the NEC require?
- Nothing; the rod is acceptable as installed
- Drive the rod deeper until it reads 10 ohms or less
- Replace it with a plate electrode
- Add a second electrode at least 6 feet away
Answer: D. NEC 250.53(A)(2) requires a single rod, pipe or plate electrode to be supplemented by another electrode unless it tests at 25 ohms or less, and 250.53(B) requires rod electrodes to be at least 6 feet apart. Once the second electrode is installed, no particular resistance has to be reached.
Topic: Grounding and bonding
9. A device box holds two 12 AWG NM cables, each with two insulated conductors and a bare equipment grounding conductor, plus one duplex receptacle and no internal clamps. Using 2.25 in³ per 12 AWG conductor, what minimum box volume is required?
- 13.50 in³
- 15.75 in³
- 18.00 in³
- 20.25 in³
Answer: B. Under NEC 314.16(B) the four insulated conductors count 4, the equipment grounding conductors together count 1, and the receptacle yoke counts 2, for 7 allowances × 2.25 in³ = 15.75 in³. Counting each bare ground separately gives 18.00 in³, and forgetting the grounds entirely gives 13.50 in³.
Topic: Box and conduit fill
10. When three or more conductors are installed in a conduit or tubing, what is the maximum percentage of the raceway's cross-sectional area they may fill?
- 31%
- 40%
- 53%
- 60%
Answer: B. NEC Chapter 9, Table 1 allows 53% fill for one conductor, 31% for two and 40% for more than two. The 60% figure applies only to nipples not over 24 inches long between enclosures, where the adjustment factors also do not apply.
Topic: Box and conduit fill
11. A 125-volt, 15-ampere receptacle is installed in the bathroom of a dwelling unit. What protection does the NEC require for it?
- GFCI protection
- AFCI protection only
- No special protection if it has a dedicated 20-ampere circuit
- An isolated-ground receptacle
Answer: A. NEC 210.8(A) requires ground-fault circuit-interrupter protection for dwelling receptacles in bathrooms, garages, outdoors, crawl spaces, basements, kitchen countertop areas, laundry areas and within 6 feet of sinks. The 20-ampere bathroom circuit required by 210.11(C)(3) is in addition to GFCI protection, not a substitute for it.
Topic: Dwelling circuits
12. A 120-volt, 15-ampere branch circuit supplies the outlets in a bedroom of a new dwelling. What protection does the NEC require for the circuit?
- GFCI protection only
- No special protection
- AFCI protection
- A surge-protective device
Answer: C. NEC 210.12 requires arc-fault circuit-interrupter protection for 120-volt, 15- and 20-ampere branch circuits supplying outlets in dwelling bedrooms, living rooms, family rooms, kitchens, hallways, closets and similar rooms. GFCI protection under 210.8 addresses shock hazard at specific locations and is a separate requirement.
Topic: Dwelling circuits
13. In a series circuit, which quantity is the same through every component?
- Current
- Voltage drop
- Power dissipated
- Resistance
Answer: A. A series circuit has one path, so the same current flows through every element, while the source voltage divides across the elements in proportion to their resistance. In a parallel circuit the reverse is true: voltage is the same across each branch and current divides.
Topic: Electrical theory
14. A 30-ohm resistor and a 60-ohm resistor are connected in parallel. What is the total resistance of the combination?
- 20 Ω
- 30 Ω
- 45 Ω
- 90 Ω
Answer: A. For two resistors in parallel, total resistance is product over sum: (30 × 60) ÷ (30 + 60) = 1,800 ÷ 90 = 20 Ω. A parallel total is always less than the smallest branch, so 30 Ω, the 45 Ω average and the 90 Ω series sum cannot be right.
Topic: Electrical theory
15. A balanced three-phase load draws 40 amperes per line at 480 volts line-to-line with unity power factor. What is the apparent power?
- 19.2 kVA
- 33.3 kVA
- 57.6 kVA
- 66.5 kVA
Answer: B. Three-phase apparent power is √3 × line volts × line amperes: 1.732 × 480 × 40 = 33,255 VA, or about 33.3 kVA. Leaving out √3 gives 19.2 kVA, and multiplying by 3 (57.6 kVA) double counts, because line voltage and line current already reflect the phase relationship.
Topic: Electrical theory
Calculators for this exam
Read the how-to guides
How to Apply the NEC 3% Voltage Drop Rule
Why voltage drop matters, where 3% is only a recommendation, the K-factor formula with a worked example, and the fixes.
5 min readHow to Do a Residential Panel Load Calculation
The NEC 220.82 optional method step by step, a 2,000 sq ft worked example that comes to 103 A, and when to use 220.40 or 220.83 instead.
5 min readHow to Size Wire for a 50-Amp EV Charger
The 125% rule, 6 AWG vs 8 AWG copper, aluminum runs, voltage drop and GFCI for a 40 A or 48 A Level 2 charger.
Video walkthroughs on YouTube. The TapForge channel posts exam tips and app demos. Subscribe to the channel.
Frequently asked questions
Is the electrician licensing exam open book?
Most states let you bring the NEC, and some allow other references, but the rules differ by state and by testing company. Check the candidate information bulletin for your exam before you start studying.
Which NEC edition is the exam based on?
The edition your state has adopted, which may be a cycle or two behind the current 2023 NEC. The bulletin names the edition; study from that book, because article numbers and some values changed between editions.
How many questions are on the real exam?
It depends on the state and the license level. Confirm the question count, time limit and passing score in your state's candidate bulletin, then practice at the same number of minutes per question.
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These questions were written by TapForge Studios for practice and are not taken from any real exam. They follow the standards and editions named above; the exam you sit may use a different edition, and the certifying body's outline governs. Not a substitute for the code books.