Master Electrician (NEC) — All Questions

A location where ignitable concentrations of flammable gases or vapors exist under normal operating conditions is classified as:

• a.Class II, Division 1
• b.Class I, Division 2
• c.Class I, Division 1✓
• d.Class III

Class I covers flammable gases/vapors; Division 1 means ignitable concentrations can exist under normal operation, so it is Class I, Division 1.2023 NEC 500.5(B)(1)

A location made hazardous by combustible dust is classified as which class?

• a.Class I
• b.Class IV
• c.Class III
• d.Class II✓

Class II locations are those hazardous because of the presence of combustible dust.2023 NEC 500.5(C)

In a Class I, Division 1 location, a sealing fitting must be installed within what distance of an enclosure containing arcing devices?

• a.18 in✓
• b.24 in
• c.12 in
• d.36 in

Seals are required within 18 in of enclosures that contain devices which may produce arcs, sparks, or high temperatures.2023 NEC 501.15(A)

What is the minimum number of receptacles required at a general care (Category 2) patient bed location?

• a.6
• b.4
• c.14
• d.8✓

General care patient bed locations require a minimum of 8 receptacles, served from the normal and/or essential systems.2023 NEC 517.18(B)

What is the minimum number of receptacles required at a critical care (Category 1) patient bed location?

• a.14✓
• b.12
• c.8
• d.10

Critical care patient bed locations require a minimum of 14 receptacles.2023 NEC 517.19(B)

The equipotential bonding grid around a permanently installed pool must use a solid copper conductor no smaller than:

• a.#4 AWG
• b.#8 AWG✓
• c.#6 AWG
• d.#10 AWG

Pool equipotential bonding must use an insulated, covered, or bare solid copper conductor not smaller than #8 AWG.2023 NEC 680.26(B)

A required convenience receptacle for a dwelling pool must be located not less than what distance from the inside pool wall?

• a.5 ft
• b.8 ft
• c.10 ft
• d.6 ft✓

At least one receptacle is required between 6 ft and 20 ft from the inside wall; the minimum setback is 6 ft.2023 NEC 680.22(A)

A wet-niche underwater luminaire operating without GFCI protection is limited to a maximum of:

• a.24 V
• b.15 V✓
• c.120 V
• d.30 V

Underwater luminaires must be GFCI protected unless they operate at not more than the low-voltage contact limit of 15 V.2023 NEC 680.23(A)

A motor disconnecting means must have an ampere rating of at least what percent of the motor full-load current?

• a.125%
• b.115%✓
• c.100%
• d.110%

The disconnecting means for a motor must be rated at least 115% of the motor full-load current.2023 NEC 430.110(A)

A single hermetic refrigerant motor-compressor has a rated-load current of 24 A. What minimum branch-circuit conductor ampacity is required?

• a.30 A✓
• b.24 A
• c.28 A
• d.36 A

Conductors to a single motor-compressor must be at least 125% of the rated-load or branch-circuit selection current: 24 x 1.25 = 30 A.2023 NEC 440.32

A hermetic compressor has a rated-load current of 24 A. What is the maximum branch-circuit short-circuit and ground-fault device at 175% (next standard size)?

• a.40 A
• b.60 A
• c.45 A✓
• d.50 A

175% of 24 A = 42 A; the next standard overcurrent size is 45 A, which is the maximum permitted for short-circuit/ground-fault protection.2023 NEC 440.22(A)

Which nameplate value on an air-conditioning unit is used to size the branch-circuit conductors?

• a.Maximum overcurrent protection
• b.Rated-load amps only
• c.Nameplate horsepower
• d.Minimum circuit ampacity✓

Conductors are sized to the marked minimum circuit ampacity (MCA); the maximum overcurrent protective device (MOCP) sizes the breaker or fuse.2023 NEC 440.4

A Class 2 power-limited circuit at 30 V or less is limited to a maximum power of:

• a.100 VA✓
• b.250 VA
• c.1,000 VA
• d.500 VA

Class 2 circuits are inherently limited low-energy circuits; a typical alternating-current source limit is 100 VA at up to 30 V for reliable low-energy protection.2023 NEC Chapter 9 Table 11(B)

Cables listed for power-limited fire alarm use are marked with which type designation?

• a.CMR
• b.CL2
• c.TC
• d.FPL✓

Power-limited fire alarm cables carry the FPL family markings (FPL, FPLR riser, FPLP plenum).2023 NEC 760.179

Two 10-HP, 460-V motors (14 A each) are supplied by one feeder. What minimum feeder conductor ampacity is required?

• a.28 A
• b.31.5 A✓
• c.25 A
• d.35 A

125% of the largest motor plus the other: (14 x 1.25) + 14 = 17.5 + 14 = 31.5 A.2023 NEC 430.24

A motor without a marked service factor (or with SF under 1.15) has a full-load current of 28 A. What is the maximum overload protection at 115%?

• a.30 A
• b.35 A
• c.28 A
• d.32.2 A✓

For motors with a service factor less than 1.15, overload protection is limited to 115% of nameplate FLA: 28 x 1.15 = 32.2 A.2023 NEC 430.32(A)

Which wiring method is acceptable in a Class I, Division 2 location?

• a.Type AC
• b.Nonmetallic Romex
• c.Type MC with listed fittings✓
• d.Type NM

Class I, Division 2 permits methods such as threaded rigid metal conduit and Type MC cable with listed fittings; ordinary NM/AC cable is not permitted.2023 NEC 501.10(B)

A required branch circuit that supplies a sign or outline lighting system must be rated at least:

• a.40 A
• b.30 A
• c.15 A
• d.20 A✓

Each commercial building must have at least one dedicated 20-A branch circuit for a sign or outline lighting outlet.2023 NEC 600.5(B)

Low-voltage lighting systems covered by Article 411 are limited to a maximum circuit voltage of:

• a.12 V
• b.30 V✓
• c.15 V
• d.24 V

Article 411 low-voltage lighting systems operate at not more than 30 V (or 60 V DC for wet contact limits), commonly through a listed power supply.2023 NEC 411.5

Electrical equipment supplying a decorative fountain must have what protection?

• a.Surge protection
• b.GFCI✓
• c.AFCI
• d.Isolation transformer only

All electrical equipment associated with fountains, including luminaires and pumps, must be protected by a ground-fault circuit interrupter.2023 NEC 680.51(A)

The equipotential plane bonding conductor in an agricultural building must be:

• a.#8 Cu only if insulated
• b.Copper conductor not smaller than #8✓
• c.#6 Cu maximum
• d.Insulated conductor only

Bonding of the equipotential plane in agricultural buildings uses a copper conductor not smaller than #8 AWG, solid or the equivalent.2023 NEC 547.10

A motor feeder supplies motors whose largest branch device is 90 A, plus other motors with 50 A total full-load current. What is the maximum feeder short-circuit/ground-fault device (not to exceed the sum, next standard down)?

• a.110 A
• b.175 A
• c.125 A✓
• d.150 A

The feeder device may not exceed the largest branch-circuit device (90 A) plus the other FLCs (50 A) = 140 A; the largest standard rating not exceeding 140 A is 125 A.2023 NEC 430.62

How many overload (running-protection) units are required for a three-phase AC motor?

• a.1
• b.2
• c.3✓
• d.4

2023 NEC Table 430.37 requires three overload units, one in each phase, for a three-phase AC motor. Trap: two units apply to certain single-phase configurations, not to three-phase motors.2023 NEC Table 430.37

An indoor dry-type transformer rated over 112.5 kVA with standard insulation generally must be installed:

• a.on any combustible wall surface
• b.within 6 in of any exposed combustible building material
• c.in a ventilated attic space
• d.in a transformer room of fire-resistant construction✓

2023 NEC 450.21(B) requires indoor dry-type transformers over 112.5 kVA to be in a fire-resistant transformer room, unless the unit uses Class 155 C or higher insulation with the specified clearances/barriers. Trap: units up to 112.5 kVA only need 12-in separation from combustibles.2023 NEC 450.21(B)

An adjustable-speed drive (VFD) has a rated input current of 30 A. What minimum branch-circuit conductor ampacity is required?

• a.37.5 A✓
• b.30 A
• c.40 A
• d.45 A

2023 NEC 430.122(A) sizes conductors to a power-conversion drive at 125% of the rated input current: 30 x 1.25 = 37.5 A. Trap: use the drive's rated input current, not the motor nameplate FLC, for a VFD circuit.2023 NEC 430.122(A)

Atmospheres containing acetylene are classified in which hazardous (classified) location group?

• a.Group D
• b.Group A✓
• c.Group C
• d.Group B

2023 NEC 500.6(A)(1) places acetylene in Class I, Group A. Trap: Group D (propane, gasoline vapor, etc.) is the most common and often assumed, but acetylene is the single Group A gas.2023 NEC 500.6(A)

The disconnecting means for air-conditioning and refrigerating equipment must be located:

• a.only at the main service panel of the building, wherever it sits
• b.at least 25 ft from the unit
• c.inside a locked room
• d.within sight from and readily accessible to it✓

2023 NEC 440.14 requires the A/C disconnect to be within sight from and readily accessible from the equipment. Trap: locating it only at the service panel does not satisfy the within-sight requirement for the unit.2023 NEC 440.14

In patient care spaces, branch-circuit wiring to receptacles and fixed equipment must provide grounding by:

• a.an insulated EGC plus the metal raceway or cable armor✓
• b.the metal raceway or cable armor alone serving as the only ground path
• c.an isolated ground connection only
• d.the grounded (neutral) conductor

2023 NEC 517.13 requires redundant grounding: an insulated copper equipment grounding conductor AND a metal raceway or cable with a metallic grounding path. Trap: the raceway alone is not sufficient in patient care spaces.2023 NEC 517.13

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.

Electrical equipment associated with a fountain, including submersible pumps and luminaires, must be protected by:

• a.an isolation transformer only
• b.an arc-fault circuit interrupter
• c.a ground-fault circuit interrupter (GFCI)✓
• d.a surge arrester

2023 NEC 680.51(A): fountain luminaires and other electrical equipment associated with the fountain must be GFCI protected.

In agricultural buildings, the site-isolating disconnecting means at the distribution point must:

• a.be a service disconnect at each building only
• b.provide a means to disconnect all site conductors and be identified as the site-isolating device✓
• c.be limited to 60 A maximum
• d.be a snap switch inside the barn

2023 NEC 547.9/547.25: the site-isolating device at the agricultural distribution point disconnects the site conductors and must be pole-mounted or otherwise identified as such.

A feeder supplies a 50-HP (65 A), a 30-HP (40 A), and a 20-HP (27 A) motor, all 460-V three-phase. What minimum feeder conductor ampacity is required?

• a.156 A
• b.140 A
• c.132 A
• d.148.25 A✓

2023 NEC 430.24: 125% of the largest motor FLC plus the sum of the others: (65 x 1.25) + 40 + 27 = 81.25 + 67 = 148.25 A.

A motor marked with a temperature rise of 40 C (and no service factor) has a nameplate full-load current of 52 A. What is the maximum overload protection?

• a.52 A
• b.59.8 A
• c.65 A✓
• d.60 A

2023 NEC 430.32(A)(1): motors marked with a temperature rise not over 40 C may set overload at 125% of nameplate FLA: 52 x 1.25 = 65 A.

In a Class II, Division 1 (combustible dust) location, enclosures for arcing equipment must be:

• a.identified (listed) as dust-ignitionproof for the location✓
• b.explosionproof for Class I only
• c.weatherproof rated
• d.ordinary NEMA 1 enclosures

2023 NEC 502.115/502.6: Class II, Division 1 arcing equipment must be in enclosures identified as dust-ignitionproof; Class I explosionproof enclosures are not necessarily suitable for dust.

An indoor dry-type transformer rated 45 kVA with standard (Class 105) insulation must maintain what minimum separation from combustible material unless otherwise protected?

• a.18 in
• b.3 in
• c.12 in✓
• d.6 in

2023 NEC 450.21(A): dry-type transformers 112.5 kVA and under must be separated at least 12 in from combustible material unless the unit has a listed fire-resistant barrier or Class 155 (or higher) insulation.

Which value from a motor nameplate must be used with the tables to size branch-circuit short-circuit protection and conductors, per 430.6(A)?

• a.the nameplate full-load amperes
• b.the service-factor amps
• c.the locked-rotor current
• d.the table full-load current, not the nameplate current rating✓

2023 NEC 430.6(A)(1): for general motor applications, the full-load current values in Tables 430.247-430.250 (not the nameplate FLA) are used to size conductors and short-circuit/ground-fault protection. Overload protection uses the nameplate FLA.

The disconnecting means for air-conditioning or refrigerating equipment with a motor-compressor must be located:

• a.only at the main service panel
• b.inside a locked mechanical room only
• c.at least 25 ft away
• d.within sight from and readily accessible from the equipment✓

2023 NEC 440.14: the disconnect must be within sight from, and readily accessible from, the air-conditioning or refrigerating equipment.

How many overload (running-protection) units are required for a three-phase alternating-current motor?

• a.one
• b.three✓
• c.four
• d.two

2023 NEC Table 430.37: a three-phase AC motor requires three overload units, one in each phase.

In patient care spaces, grounding of receptacles and fixed electrical equipment must be accomplished by:

• a.an isolated ground only
• b.the metal raceway alone as the only ground path
• c.the grounded (neutral) conductor
• d.an insulated copper equipment grounding conductor plus a metal raceway or cable armor (redundant ground)✓

2023 NEC 517.13: patient care spaces require redundant grounding - an insulated copper EGC AND a metallic raceway or cable that itself qualifies as a grounding path.

The disconnecting means for a motor must have an ampere rating of at least what percentage of the motor full-load current?

• a.115%✓
• b.125%
• c.100%
• d.110%

2023 NEC 430.110(A): the disconnecting means for a motor circuit must be rated at least 115% of the motor full-load current.