Master Electrician (NEC) — All Questions
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66 questions
A 208-V, three-phase feeder supplies a 120,000-VA load. What is the calculated feeder current?
- a.577 A
- b.288 A
- c.333 A✓
- d.200 A
Three-phase current = 120,000 / (1.732 x 208) = 333 A.
A 225-A busbar is fed by a 225-A main breaker at one end. Using the 120% rule, what is the maximum back-fed inverter (PV) supply breaker at the opposite end?
- a.60 A
- b.45 A✓
- c.40 A
- d.30 A
2023 NEC 705.12(B)(3): 120% of the 225-A busbar = 270 A; subtract the 225-A main: 270 - 225 = 45 A maximum for the back-fed supply breaker.
A feeder is protected by a 500-A overcurrent device. What is the minimum copper equipment grounding conductor?
- a.#2 AWG✓
- b.#3 AWG
- c.#4 AWG
- d.#1 AWG
2023 NEC Table 250.122: a 500-A overcurrent device requires a #2 Cu equipment grounding conductor.
A feeder is protected by an 800-A overcurrent device. What is the minimum copper equipment grounding conductor?
- a.1/0 AWG✓
- b.#2 AWG
- c.#1 AWG
- d.2/0 AWG
2023 NEC Table 250.122: an 800-A overcurrent device requires a 1/0 Cu equipment grounding conductor.
A feeder is protected by a 1,200-A overcurrent device. What is the minimum copper equipment grounding conductor?
- a.3/0 AWG✓
- b.4/0 AWG
- c.#1 AWG
- d.2/0 AWG
2023 NEC Table 250.122: a 1,200-A overcurrent device requires a 3/0 Cu equipment grounding conductor.
A service uses 1/0 AWG copper ungrounded conductors. What is the minimum copper grounding electrode conductor?
- a.#4 AWG
- b.#2 AWG
- c.#6 AWG✓
- d.#8 AWG
2023 NEC Table 250.66: service conductors of 1 or 1/0 Cu require a #6 Cu grounding electrode conductor.
A service uses 750-kcmil copper ungrounded conductors. What is the minimum copper grounding electrode conductor?
- a.2/0 AWG✓
- b.3/0 AWG
- c.1/0 AWG
- d.#1 AWG
2023 NEC Table 250.66: over 600 through 1,100 kcmil Cu requires a 2/0 Cu grounding electrode conductor.
A separately derived system (transformer) has 600-kcmil copper derived conductors. What is the minimum copper supply-side bonding jumper?
- a.1/0 AWG✓
- b.#1 AWG
- c.2/0 AWG
- d.#2 AWG
2023 NEC 250.30(A)(2) with Table 250.102(C)(1): over 350 through 600 kcmil Cu requires a 1/0 Cu bonding jumper.
Service-entrance conductors supply a 150-A continuous load. What minimum conductor ampacity is required?
- a.187.5 A✓
- b.150 A
- c.200 A
- d.165 A
2023 NEC 230.42(A): service conductors must carry at least 125% of the continuous load: 150 x 1.25 = 187.5 A.
A service has 3/0 AWG copper ungrounded conductors. What is the minimum copper bonding jumper for the metal underground water pipe?
- a.#2 AWG
- b.#6 AWG
- c.#4 AWG✓
- d.#8 AWG
2023 NEC 250.104(A)(1) sizes the water-pipe bonding jumper from Table 250.66: 2/0-3/0 Cu service conductors require a #4 Cu bonding jumper.
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Under 2023 NEC 110.9, a circuit breaker or fuse intended to interrupt fault current must have an interrupting rating that is:
- a.125% of the continuous load
- b.equal to the connected load current
- c.at least the available fault current at its line terminals✓
- d.the same as the largest downstream conductor ampacity
2023 NEC 110.9 requires the device's interrupting rating to be at least the available fault current where it is applied; ampacity and load current size the device only for normal operation.
A downstream circuit breaker has an interrupting rating below the available fault current. It may still be applied only if:
- a.the connected load is noncontinuous
- b.it is a molded-case type
- c.it is derated 20% for continuous operation
- d.it is part of a listed, tested series combination with the line-side device✓
2023 NEC 240.86 permits a lower-rated downstream breaker only as part of a tested, marked series combination with the line-side OCPD (or under engineering supervision). Derating does not raise interrupting rating.
Service phase conductors total 1,100 kcmil Cu per phase. Using the bonding table, what is the minimum copper main bonding jumper?
- a.1/0 AWG
- b.2/0 AWG✓
- c.#1 AWG
- d.3/0 AWG
2023 NEC 250.28(D)(1) with Table 250.102(C)(1): over 600 through 1,100 kcmil Cu requires a 2/0 Cu main bonding jumper.
What is the maximum rating of the overcurrent device that may protect a 400-A-rated panelboard?
- a.350 A
- b.450 A
- c.400 A✓
- d.500 A
2023 NEC 408.36: a panelboard must be protected by an overcurrent device rated no more than the panelboard rating, so 400 A is the maximum.
A single made electrode (ground rod) must be supplemented by a second electrode unless its resistance to earth does not exceed:
- a.1 ohm
- b.5 ohms
- c.25 ohms✓
- d.10 ohms
2023 NEC 250.53(A)(2): a single rod, pipe, or plate electrode must be supplemented unless it has a resistance to earth of 25 ohms or less.
A branch circuit is protected by a 30-A overcurrent device. What is the minimum copper equipment grounding conductor?
- a.#12 AWG
- b.#10 AWG✓
- c.#14 AWG
- d.#8 AWG
2023 NEC Table 250.122: overcurrent devices from 30 through 60 A require a #10 Cu equipment grounding conductor.
How hard is the exam?
Master electrician licensing is state-administered and NEC-based, so format varies by state. In Texas, for example, the exam has two open-book portions (2023 NEC) — 75 NEC-knowledge items and 33 calculation items (108 total) — each needing 70% to pass, for a $78 fee. Electricians earn a median of about $62,350/year (BLS, May 2024).
- Recommended study hours
- 80-150 hours for most — master exams add heavier calculations and code-application depth over journeyman.
- Published pass rate
- 19.08% (the source does not say which attempts it counts) (n = 3,946); 22.21% (the source does not say which attempts it counts) (n = 3,472) — Texas TDLR, FY 2025. Read those as two exams, not one: TDLR has no row called “Master Electrician”, only “Master Calculations” (the first figure) and “Master NEC” (the second). Anyone quoting a single 19% Texas master pass rate has silently dropped half the exam. Licensing is state by state, so this is Texas only.Source: Texas TDLR — Electrician Exam Statistics, Fiscal Year 2025
- Where to focus first
- Services, service equipment and separately derived systems is among the heaviest areas (about 18% in Texas), plus the load-calculation portion.
Fees and salaries are approximate and change over time. The pass rate above is quoted from the source linked beside it, for the period that source covers — where we have not checked a source, we say so and give no number.