Master Electrician (NEC) — All Questions
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300 questions
A service uses #3/0 AWG copper ungrounded conductors. What is the minimum copper grounding electrode conductor?
- a.#8 AWG
- b.#6 AWG
- c.#2 AWG
- d.#4 AWG✓
2023 NEC Table 250.66: for service conductors over 1/0 through 3/0 Cu, the grounding electrode conductor is #4 Cu.
A service uses 400-kcmil copper ungrounded conductors. What is the minimum copper grounding electrode conductor?
- a.1/0 AWG✓
- b.#2 AWG
- c.#3 AWG
- d.#1 AWG
2023 NEC Table 250.66: over 350 through 600 kcmil Cu requires a 1/0 Cu grounding electrode conductor.
Where the grounding electrode conductor connects solely to a concrete-encased (Ufer) electrode, what is the largest copper size it is ever required to be?
- a.#2 AWG
- b.#4 AWG✓
- c.#8 AWG
- d.#6 AWG
2023 NEC 250.66(B): the portion of the GEC that connects only to a concrete-encased electrode need not be larger than #4 Cu.
A branch circuit is protected by a 60-A overcurrent device. What is the minimum copper equipment grounding conductor?
- a.#12 AWG
- b.#8 AWG
- c.#6 AWG
- d.#10 AWG✓
2023 NEC Table 250.122: overcurrent devices up to 60 A require a #10 Cu equipment grounding conductor.
A feeder is protected by a 200-A overcurrent device. What is the minimum copper equipment grounding conductor?
- a.#6 AWG✓
- b.#4 AWG
- c.#8 AWG
- d.#10 AWG
2023 NEC Table 250.122: a 200-A overcurrent device requires a #6 Cu equipment grounding conductor.
A feeder is protected by a 600-A overcurrent device. What is the minimum copper equipment grounding conductor?
- a.#1 AWG✓
- b.#3 AWG
- c.#2 AWG
- d.1/0 AWG
2023 NEC Table 250.122: a 600-A overcurrent device requires a #1 Cu equipment grounding conductor.
A service has 3/0 AWG copper ungrounded conductors. What is the minimum copper grounded (neutral) service conductor for bonding purposes?
- a.#6 AWG
- b.#4 AWG✓
- c.#2 AWG
- d.#8 AWG
2023 NEC 250.24(C) with Table 250.102(C)(1): for 2/0-3/0 Cu phase conductors, the grounded service conductor is at least #4 Cu.
Service ungrounded conductors are 350-kcmil copper per phase. Using the bonding table, what is the minimum copper main bonding jumper?
- a.#1 AWG
- b.#2 AWG✓
- c.#4 AWG
- d.1/0 AWG
2023 NEC 250.28(D)(1) with Table 250.102(C)(1): over 3/0 through 350 kcmil Cu requires a #2 Cu main bonding jumper.
Service phase conductors total 2,000 kcmil Cu per phase (over 1,100 kcmil). Using the 12.5% rule, what is the minimum copper main bonding jumper?
- a.3/0 AWG
- b.350 kcmil
- c.250 kcmil✓
- d.4/0 AWG
2023 NEC 250.28(D)(2): above 1,100 kcmil the main bonding jumper is at least 12.5% of the phase area: 0.125 x 2,000 = 250 kcmil.
A feeder supplies a detached building. Under 2023 NEC 250.32, the feeder must include which of the following?
- a.an equipment grounding conductor run with the feeder to the building✓
- b.a separate utility service
- c.no grounding conductor if the feeder is under 100 A
- d.a bonded neutral serving as the only ground path
2023 NEC 250.32(B) requires an equipment grounding conductor run with the supply to the separate building, with the neutral kept isolated from ground at the second building.
Where two ground rods are used as the grounding electrode, what is the minimum required spacing between them?
- a.8 ft
- b.3 ft
- c.10 ft
- d.6 ft✓
2023 NEC 250.53(A)(3): rod, pipe, or plate electrodes that supplement each other must be at least 6 ft apart.
A driven ground rod electrode must have a minimum length in contact with the soil of:
- a.10 ft
- b.6 ft
- c.4 ft
- d.8 ft✓
2023 NEC 250.52(A)(5) and 250.53(G): rod electrodes must be at least 8 ft in length and installed with at least 8 ft in contact with the soil.
Overhead service-drop conductors must maintain what minimum vertical clearance above public streets, roads, and alleys?
- a.15 ft
- b.12 ft
- c.18 ft✓
- d.10 ft
2023 NEC 230.24(B)(4): 18 ft over public streets, alleys, roads, and areas subject to truck traffic.
Absent a specific exception, what is the maximum overcurrent protection for a #14 Cu conductor?
- a.25 A
- b.10 A
- c.20 A
- d.15 A✓
2023 NEC 240.4(D): under the small-conductor rule, #14 Cu is limited to a 15-A overcurrent device.
A conductor has an allowable ampacity of 240 A, which is not a standard rating. Under the next-standard-size rule (800 A or less), what is the largest permitted overcurrent device?
- a.225 A
- b.250 A✓
- c.300 A
- d.240 A
2023 NEC 240.4(B): when ampacity does not match a standard rating and conditions are met, the next higher standard device is permitted; the next standard size above 240 A is 250 A.
A 400-A feeder is run as two parallel sets of conductors in separate raceways. What is required for the equipment grounding conductor in each raceway?
- a.a #6 Cu EGC, split half in each raceway
- b.a #8 Cu EGC in each raceway
- c.a single #3 Cu total for the run
- d.a full-size EGC in each raceway, sized to the 400-A device (#3 Cu)✓
2023 NEC 250.122(F): each parallel raceway must contain a full-size EGC sized to the feeder device; Table 250.122 gives #3 Cu for 400 A. The EGC is never divided among the raceways.
A service has 250-kcmil copper ungrounded conductors. What is the minimum copper grounded (neutral) service conductor required by 250.24(C)?
- a.1/0 AWG
- b.#4 AWG
- c.#2 AWG✓
- d.#1 AWG
2023 NEC 250.24(C) with Table 250.102(C)(1): over 3/0 through 350 kcmil Cu (which includes 250 kcmil) requires a #2 Cu grounded conductor.
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.
A single hermetic refrigerant motor-compressor has a rated-load current of 28 A. What minimum branch-circuit conductor ampacity is required?
- a.35 A✓
- b.28 A
- c.40 A
- d.31.5 A
2023 NEC 440.32: conductors to a single motor-compressor must be at least 125% of the rated-load current: 28 x 1.25 = 35 A.
A hermetic compressor has a rated-load current of 28 A. What is the maximum branch-circuit short-circuit and ground-fault device at 175% (next standard size)?
- a.50 A✓
- b.40 A
- c.45 A
- d.60 A
2023 NEC 440.22(A): 175% of 28 A = 49 A; the next standard overcurrent size is 50 A, the maximum permitted for short-circuit/ground-fault protection.
An A/C unit has a compressor rated-load current of 20 A and a fan motor of 3 A. What minimum branch-circuit conductor ampacity is required?
- a.30 A
- b.25 A
- c.28 A✓
- d.23 A
2023 NEC 440.33/440.34: 125% of the largest motor plus the other loads: (20 x 1.25) + 3 = 25 + 3 = 28 A.
A location where ignitable concentrations of flammable gas or vapor are present only under abnormal (fault or leak) conditions is classified as:
- a.Class I, Division 1
- b.Class I, Division 2✓
- c.Class III
- d.Class II, Division 1
2023 NEC 500.5(B)(2): Class I, Division 2 covers flammable gases or vapors normally confined but present only under abnormal conditions.
A location made hazardous by easily ignitable fibers or flyings that are not likely to be suspended in the air is classified as:
- a.Class IV
- b.Class II
- c.Class I
- d.Class III✓
2023 NEC 500.5(D): Class III locations are hazardous because of easily ignitable fibers or flyings, such as textile mills and woodworking areas.
Atmospheres containing propane, gasoline, or natural-gas vapor fall into which hazardous-location group?
- a.Group D✓
- b.Group B
- c.Group A
- d.Group C
2023 NEC 500.6(A)(4): Group D includes the common flammable gases and vapors such as propane, gasoline, and natural gas.
In a Class I, Division 1 location, where a conduit leaves the classified area into an unclassified area, a seal is required:
- a.never, if rigid metal conduit is used
- b.only at the service equipment
- c.only if the conduit is over 2 in trade size
- d.within 10 ft of the boundary, with no coupling or fitting between the seal and the boundary except as permitted✓
2023 NEC 501.15(A)(4): a seal is required within 10 ft of the boundary where a raceway leaves a Class I, Division 1 location, with no unions, couplings, or fittings between the seal and the point of exit (other than as allowed).
A hospital's essential electrical system for a Type 1 facility is divided into which branches?
- a.isolated and grounded branches
- b.life safety, critical, and equipment branches✓
- c.emergency and legally required branches
- d.normal and standby branches only
2023 NEC 517.30: the Type 1 essential electrical system consists of the life safety branch, the critical branch, and the equipment branch.
In a wet procedure location where interruption of power is not permitted, protection is provided by:
- a.double-insulated equipment only
- b.an AFCI on the branch circuit
- c.standard 15-A receptacles only
- d.an isolated power system (or GFCI where interruption can be tolerated)✓
2023 NEC 517.20: wet procedure locations require GFCI protection or an isolated power system; where power interruption cannot be tolerated, an isolated (ungrounded) power system is used.
Luminaires and lighting outlets installed over a permanently installed pool must be mounted at least what height above the maximum water level (for new installations without special protection)?
- a.8 ft
- b.12 ft✓
- c.10 ft
- d.5 ft
2023 NEC 680.22(B): luminaires over the pool and the area extending 5 ft horizontally must be at least 12 ft above the maximum water level for new work.
The equipotential bonding required around a permanently installed pool must extend horizontally what distance from the inside pool wall?
- a.5 ft
- b.2 ft
- c.3 ft✓
- d.6 ft
2023 NEC 680.26(B)(2): the perimeter surface equipotential bonding extends 3 ft horizontally beyond the inside walls of the pool.
Outlets supplying a self-contained spa or hot tub must be protected by:
- a.an isolation transformer only
- b.a ground-fault circuit interrupter (GFCI)✓
- c.an arc-fault circuit interrupter
- d.a surge protective device
2023 NEC 680.44: the outlet(s) that supply a self-contained or packaged spa or hot tub must be GFCI protected.
A motor controller (other than certain small or torque motors) must have a horsepower rating that is:
- a.equal to the branch-circuit device rating
- b.at least 250% of the motor horsepower
- c.at least equal to the motor horsepower at the application voltage✓
- d.not more than the motor full-load current
2023 NEC 430.83(A): the controller must have a horsepower rating not lower than the motor horsepower rating at the application voltage, so it can make and break the motor current.
An adjustable-speed drive (VFD) has a rated input current of 24 A. What minimum branch-circuit conductor ampacity is required?
- a.36 A
- b.30 A✓
- c.24 A
- d.28 A
2023 NEC 430.122(A): conductors supplying a power-conversion drive are sized at 125% of the rated input current: 24 x 1.25 = 30 A. Use the drive input current, not the motor FLC.
The disconnecting means for a sign or outline lighting system must be:
- a.at the utility transformer only
- b.within sight of the sign or controller, or capable of being locked open✓
- c.inside a locked electrical room only
- d.at least 25 ft from the sign
2023 NEC 600.6(A): the sign disconnect must be within sight of the sign or outline lighting it controls, or be lockable in the open position where out of sight.
Each commercial building or occupancy accessible to pedestrians must have at least one dedicated sign or outline-lighting branch circuit rated at least:
- a.20 A✓
- b.30 A
- c.40 A
- d.15 A
2023 NEC 600.5(A): at least one dedicated 20-A branch circuit is required for a sign or outline-lighting outlet at each entrance of a commercial occupancy.
Article 411 low-voltage lighting systems are limited to a maximum circuit voltage of:
- a.30 V✓
- b.24 V
- c.15 V
- d.12 V
2023 NEC 411.5: low-voltage lighting systems operate at a maximum of 30 V ac (or 60 V dc for dry locations), typically through a listed power supply.
¿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.