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.
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.
¿Qué tan difícil es el examen?
La licencia de electricista maestro la administra cada estado y se basa en el NEC, así que el formato varía por estado. En Texas, por ejemplo, el examen tiene dos partes a libro abierto (NEC 2023) — 75 ítems de conocimiento del NEC y 33 ítems de cálculo (108 en total) — cada una requiere 70% para aprobar, por una tarifa de $78. Los electricistas ganan una mediana de unos $62,350 al año (BLS, mayo 2024).
- Horas de estudio recomendadas
- 80-150 horas para la mayoría — los exámenes de maestro agregan cálculos más pesados y mayor profundidad de aplicación del código que el de oficial.
- Tasa de aprobación publicada
- 19.08% (la fuente no dice qué intentos cuenta) (n = 3,946); 22.21% (la fuente no dice qué intentos cuenta) (n = 3,472) — Texas TDLR, FY 2025. Léelas como dos exámenes, no uno: TDLR no tiene fila llamada “Master Electrician”, solo “Master Calculations” (la primera cifra) y “Master NEC” (la segunda). Quien cite un único 19% de master en Texas ha descartado en silencio la mitad del examen. La licencia es estatal, así que esto es solo Texas.Fuente: Texas TDLR — Electrician Exam Statistics, Fiscal Year 2025
- Por dónde empezar
- Servicios, equipo de servicio y sistemas derivados por separado está entre las áreas más pesadas (cerca del 18% en Texas), más la parte de cálculo de cargas.
Las tarifas y los salarios son aproximados y cambian con el tiempo. La tasa de aprobación de arriba se cita de la fuente enlazada junto a ella, para el periodo que esa fuente cubre; cuando no hemos verificado una fuente, lo decimos y no damos ninguna cifra.