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Idaho Master Electrician Practice Exam

What This Practice Exam Covers

The Idaho Master Electrician Exam is a 100-question test with a 270-minute time limit. You need a 75% (75 correct answers) to pass. The exam spans eight topic areas drawn directly from the 2023 NEC and covers everything from Ohm's Law calculations to hazardous location classifications to solar PV rapid shutdown requirements.

This practice site gives you two ways to prepare:

• Free practice exam: 10 questions per attempt pulled from a limited pool. You can retake it as many times as you want to get comfortable with the question format and difficulty level before committing to serious prep.
• Full practice exam (paid): Mirrors the real exam exactly — 100 questions, 270-minute time limit, scored to the 75% passing threshold. Questions are drawn from a pool of 368+ items, so each attempt presents a unique combination. No two attempts are identical, which means repeated attempts continue to expose new gaps rather than just reinforcing questions you've already memorized.

Start with the free exam to calibrate where you stand, then use the full exam for structured preparation.

What You'll Be Tested On

General Electrical Knowledge — 10 Items

This section rewards candidates who can do math quickly and accurately. Expect Ohm's Law calculations (V = IR, P = IV, P = I²R) applied to realistic circuit scenarios — given two values, solve for the third. Series circuit rules show up here too, including total resistance, current, and voltage drop across individual resistors. You also need to know the NEC's structure: Article 90 governs scope, arrangement, and rule language. Under NEC 90.5(A), mandatory rules use "shall"; permissive rules use "shall be permitted"; explanatory material appears as fine print notes. NEC 90.2(D) lists what the Code does not cover. Know the difference between 120/240V single-phase and three-phase distribution systems, and memorize conductor color-coding conventions for each per NEC 110.15 and Common Electrical Distribution Systems.

Wiring and Protection — 25 Items

The heaviest topic on the exam. You must be able to apply NEC Table 310.16 to size conductors, then apply correction factors for ambient temperature and adjustment factors for more than three current-carrying conductors (NEC 2023, Section 310.15(B)(2)). Grounding electrode system questions are frequent — know the order of electrodes, conductor sizing from NEC 2023, Table 250.122, and bonding rules including NEC 2023, Section 250.64(B)(2) and NEC 2023, Section 250.53(A)(2). Service entrance questions cover minimum conductor size (NEC 2023, Section 310.12(A), Table 310.12(A)), disconnect location (NEC 2023, Section 230.79(D)), and ground-fault protection at 1000A or more (NEC 2023, Section 230.95). Underground wiring questions require you to recall minimum cover depths from NEC 2023, Table 300.5(A) by wiring method and circuit voltage.

Wiring Methods and Materials — 20 Items

Box fill is tested on nearly every sitting. You count conductors using NEC Table 314.16(B)(1): each unbroken conductor through the box, each conductor originating or terminating in the box, grounds as one total, devices as two conductors each. Compare your total volume against NEC Table 314.16(A). Physical protection of cables through studs and joists appears under NEC 300.4(A)(1) and NEC 300.4(A)(2) — know the 1¼-inch edge-distance rule and when a nail plate is required. Wiring in ducts and plenums is restricted by NEC 2023, Section 300.22(C)(1): only specific wiring methods are permitted where air is circulated for HVAC purposes.

Equipment for General Use — 20 Items

This section covers day-to-day hardware in detail. Fixture wire ampacity and voltage limits come from NEC Table 402.5 and NEC, Section 402.6. Receptacle rules include GFCI requirements, tamper-resistant mandates, and replacement grounding rules (NEC 406.3(F), NEC 406.4(D)(3), Exception). Switch ratings and configurations are tested — including when a grounded conductor must be brought to the switch location (NEC 404.2(C)) and when AC general-use snap switches may control fluorescent ballasts (NEC 404.14(A)). Luminaire location questions ask whether a listed wet-location or damp-location fixture is required based on proximity to showers, bathtubs, or outdoor exposure (NEC 410.10(A)). Flexible cord prohibited uses — substituting for permanent wiring, running through walls, concealed in ceilings — are spelled out in NEC 400.12.

Special Occupancies — 11 Items

Hazardous location classification dominates this section. You need to know Class I (flammable gases/vapors), Class II (combustible dusts), and Class III (ignitable fibers), along with Division 1 vs. Division 2 distinctions. Commercial garage classification appears under NEC 511.3 and Article 511.3(C), Table 511.3(C). Motor fuel dispensing facilities are governed by NEC 514.8 and Article 514.8(A). Health care facility questions reference essential electrical system branches (life safety, critical) under Article 517.31(C)(3) and patient care space grounding and receptacle requirements (Article 517.18(B)(1), Article 517.19(C)(1)). Swimming pool bonding, GFCI protection, and luminaire setback distances are tested separately from general luminaire rules — know the specific distances and grounding requirements.

Special Equipment — 6 Items

Cranes, hoists, elevators, generators, and electric signs each carry their own rules. Crane conductor sizing comes from NEC 610.14(C); the disconnecting means for cranes must be lockable per Article 610.21(D). Elevator branch circuit and feeder sizing involves demand factors (NEC 620.22(A)). Generator questions test overcurrent protection sizing, disconnecting means, and marking requirements — NEC 445.6 and NEC, Section 445.13(A) appear frequently. Electric sign disconnects must be within sight of the sign per Article 600.23(C), and signs must be grounded per NEC 600.5(A).

Special Conditions — 5 Items

Solar PV is the primary focus. Maximum system voltage calculations, overcurrent protection, and arc-fault protection requirements come from NEC 690.7 and NEC 690.11. Rapid shutdown requirements for rooftop PV systems are covered under NEC 690.12(B)(1); wiring method requirements for PV source circuits appear in NEC 690.31(D)(1). Hazardous location protection techniques — explosionproof, dust-ignitionproof, intrinsically safe, purged/pressurized — are also tested here, overlapping with Special Occupancies content.

Communication Systems — 3 Items

A smaller topic but one where unprepared candidates drop easy points. Cable listing requirements by location (plenum, riser, general-purpose) come from NEC, Section 800.113(C)(1) and NEC, Section 800.113(D). Grounding of primary protectors is addressed at NEC, Section 800.100(A)(4). Separation requirements between communications cables and power conductors appear in NEC, Section 800.133(A)(3) Exception No. 2 and NEC, Section 800.133(B).

Worked Sample Questions

Question 1 — Wiring and Protection

What is the minimum copper conductor size for a 200A residential service using THHN at 75°C terminals?

• A. 2/0 AWG
• B. 3/0 AWG
• C. 250 kcmil
• D. 300 kcmil

Correct Answer: B — 3/0 AWG

Go to NEC Table 310.16 (reproduced in NEC 2023, Section 310.12(A), Table 310.12(A) for service conductors). In the 75°C column for copper, 3/0 AWG carries exactly 200A. The terminal rating matters: if terminals are rated only 60°C, you'd have to use the 60°C column and bump up to 4/0. But with 75°C-rated terminals — standard for equipment at this ampacity — 3/0 CU is the minimum compliant size. Answer A (2/0) is only rated 175A at 75°C. Answers C and D are oversized and not the minimum.

Question 2 — Wiring Methods and Materials

A 4-inch square box (30 cu in) contains 5 conductors, 1 device, and 1 ground. Is this box compliant?

• A. Yes
• B. No

Correct Answer: A — Yes

Apply NEC Table 314.16(B)(1). Assume the conductors are #12 AWG (2 cu in each). Count as follows: 5 conductors = 10 cu in; 1 device = 2 conductors' worth = 4 cu in; all grounds count as one conductor = 2 cu in. Total fill = 16 cu in. (Even using #14 AWG at 2 cu in each with a slightly different calculation, the total stays well under 30 cu in.) The box at 30 cu in has ample capacity. This question tests whether you remember the device fill rule (two conductors, not one) and the ground fill rule (all grounds combined = one conductor).

Question 3 — Equipment for General Use

For recessed incandescent luminaires, thermal protection is NOT required when installed in which location?

• A. Suspended ceilings
• B. Poured concrete
• C. Wood frame construction
• D. Drywall ceilings

Correct Answer: B — Poured concrete

Per NEC 410.115(B), Exception No. 1, thermal protection is not required for a recessed luminaire identified for use in and installed in poured concrete. The rationale is that concrete cannot ignite, so the fire risk that thermal protection guards against simply does not apply. All other options — suspended ceilings, wood frame, and drywall — involve combustible or thermally sensitive surroundings where thermal protection is required.

How to Read Your Score

The passing threshold is 75% — 75 correct out of 100 questions. That sounds straightforward, but a single practice score does not tell you whether you're ready. Treat your first full-practice attempt as a diagnostic, not a verdict.

Look at your score topic by topic, not just overall. A candidate who scores 90% on General Electrical Knowledge but 55% on Wiring and Protection has a problem: Wiring and Protection is worth 25 items on the real exam, making it the single biggest lever available. A few percentage points of improvement in that topic can swing your total score more than maxing out a lighter section.

If you're scoring 75–79% on practice exams, that margin is thin. The real exam includes unfamiliar phrasing and scenario variations you won't have seen in practice. Candidates scoring in this range should continue drilling the full-exam pool until they're consistently hitting 82–85% before sitting for the real test.

Use wrong answers actively: look up every code section cited in the explanation, read the actual rule, and note whether it's a mandatory, permissive, or explanatory provision (NEC 90.5(A)). That habit builds the code fluency the exam actually rewards.

Where Candidates Lose Points

Wiring and Protection is where most candidates hemorrhage points. Common errors include using the wrong temperature column in NEC Table 310.16 — applying the 90°C ampacity without checking that terminals are rated for it — and forgetting to apply adjustment factors when more than three current-carrying conductors share a raceway (NEC 2023, Section 310.15(B)(2)).

Box fill calculations trip up candidates who forget the device-fill rule (a single device counts as two conductors) or who miscalculate the ground fill (all grounds count as only one, regardless of quantity). These errors consistently appear in Wiring Methods and Materials questions.

In Special Occupancies, candidates confuse Division 1 and Division 2 area classifications for commercial garages and fuel dispensing facilities. The boundaries defined in NEC 511.3 and NEC Table 514.3(B)(1) require specific memorization — guessing costs points.

On Solar PV questions under Special Conditions, candidates apply incorrect voltage calculation methods — forgetting that PV source-circuit voltage must be calculated using the temperature-corrected open-circuit voltage per NEC 690.7.

Time management is also a real risk. With 100 questions in 270 minutes, you have 2 minutes and 42 seconds per question. Multi-step calculations in Wiring and Protection can eat 5+ minutes if you're uncertain, leaving you rushing through Equipment for General Use questions that should be straightforward.

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