Master Electrician (NEC) — All Questions

A feeder supplies a 60,000-VA, 208-V, three-phase load. What is the calculated feeder current?

• a.144 A
• b.167 A✓
• c.200 A
• d.150 A

Three-phase current = 60,000 / (1.732 x 208) = 166.6 A, about 167 A.

A 200-A busbar has a 200-A main breaker at one end. Using the 120% rule, what is the maximum back-fed inverter (PV) overcurrent device at the opposite end?

• a.30 A
• b.40 A✓
• c.60 A
• d.20 A

120% of the 200-A busbar = 240 A. Subtract the 200-A main: 240 - 200 = 40 A maximum for the back-fed supply breaker.2023 NEC 705.12(B)

A single made electrode (ground rod) must be supplemented unless its resistance to earth does not exceed what value?

• a.10 ohms
• b.1 ohm
• c.25 ohms✓
• d.5 ohms

A single rod, pipe, or plate electrode must be supplemented by a second electrode unless it has a resistance to earth of 25 ohms or less.2023 NEC 250.53(A)

A metal underground water pipe qualifies as a grounding electrode if it is in direct contact with earth for at least how many feet?

• a.10 ft
• b.3 ft
• c.1 ft
• d.5 ft✓

A metal underground water pipe electrode must have at least 10 ft of contact with earth (bonding connection made within 5 ft of entry).2023 NEC 250.52(A)(1)

A concrete-encased electrode (Ufer) must consist of at least how many feet of #4 or larger rebar or bare #4 Cu conductor?

• a.20 ft✓
• b.15 ft
• c.25 ft
• d.10 ft

A concrete-encased electrode requires at least 20 ft of 1/2-in (or larger) rebar or 20 ft of bare #4 Cu encased in the concrete footing/foundation.2023 NEC 250.52(A)(3)

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

A load draws 80 kW of real power and 100 kVA of apparent power. What is the power factor?

• a.1.0
• b.0.6
• c.0.8✓
• d.0.9

Power factor = real power / apparent power = 80 kW / 100 kVA = 0.8.

For a load of 80 kW real and 100 kVA apparent, what is the reactive power?

• a.80 kVAR
• b.60 kVAR✓
• c.40 kVAR
• d.100 kVAR

Reactive power = sqrt(kVA^2 - kW^2) = sqrt(100^2 - 80^2) = sqrt(3,600) = 60 kVAR.

What is the real power of a three-phase load at 480 V, 50 A, and 0.85 power factor?

• a.35,326 W✓
• b.24,960 W
• c.30,000 W
• d.41,568 W

P = 1.732 x V x I x PF = 1.732 x 480 x 50 x 0.85 = 35,326 W.

In a balanced wye (star) three-phase system, the line current is:

• a.0.577 times the phase current
• b.Equal to the phase current✓
• c.1.732 times the phase current
• d.2 times the phase current

In a wye connection the same conductor carries phase and line current, so line current equals phase current.

In a balanced delta three-phase system, the line current equals:

• a.3 times the phase current
• b.0.577 times the phase current
• c.The phase current
• d.1.732 times the phase current✓

In a delta connection the line current is the square root of 3 (1.732) times the phase (winding) current.

In a 208Y/120-V wye system, what is the phase (line-to-neutral) voltage?

• a.208 V
• b.120 V✓
• c.277 V
• d.240 V

Line-to-neutral voltage = line-to-line / 1.732 = 208 / 1.732 = 120 V.

In a 480Y/277-V system, what is the line-to-neutral voltage?

• a.240 V
• b.120 V
• c.277 V✓
• d.208 V

Line-to-neutral = 480 / 1.732 = 277 V.

An 80-kW load at 0.80 power factor is to be corrected to 0.95. How many kVAR of capacitance are required (tan 36.87 = 0.75, tan 18.19 = 0.329)?

• a.48 kVAR
• b.60 kVAR
• c.33.7 kVAR✓
• d.20 kVAR

Qc = kW x (tan(theta1) - tan(theta2)) = 80 x (0.750 - 0.329) = 80 x 0.421 = 33.7 kVAR.

In a three-phase, four-wire wye system serving nonlinear loads, which harmonic order adds arithmetically in the neutral?

• a.7th
• b.2nd
• c.5th
• d.3rd✓

Triplen harmonics, principally the 3rd, are in phase across all three phases and add in the neutral rather than canceling.

On a feeder with significant harmonic (nonlinear) load, the neutral conductor is treated as:

• a.Not a current-carrying conductor
• b.A current-carrying conductor✓
• c.An ignored conductor
• d.A half current-carrying conductor

Where the major portion of the load is nonlinear, the neutral carries harmonic current and must be counted as a current-carrying conductor for adjustment.2023 NEC 310.15(E)

A three-phase panel has phase loads of A = 40 A, B = 30 A, C = 20 A. What is the ideal balanced current per phase?

• a.20 A
• b.40 A
• c.25 A
• d.30 A✓

Total = 40 + 30 + 20 = 90 A; balanced across three phases = 90 / 3 = 30 A per phase.

A single-line (one-line) diagram represents an electrical system by:

• a.Only the branch-circuit wiring
• b.The physical layout of raceways
• c.One line for each circuit or set of conductors✓
• d.Each individual conductor drawn separately

A one-line diagram uses a single line and standard symbols to represent circuits and equipment, simplifying analysis of the power system.

A transformer steps 480 V down to 120 V. What is its turns (voltage) ratio?

• a.4:1✓
• b.8:1
• c.2:1
• d.1:4

Turns ratio = primary voltage / secondary voltage = 480 / 120 = 4:1.

A transformer has a 4:1 turns ratio and a 10-A primary current. What is the secondary current (ideal)?

• a.2.5 A
• b.40 A✓
• c.10 A
• d.20 A

Current is inversely proportional to the turns ratio: Is = Ip x (Np/Ns) = 10 x 4 = 40 A.

An AC circuit at 240 V draws 12 A. What is the circuit impedance?

• a.0.05 ohms
• b.2 ohms
• c.20 ohms✓
• d.288 ohms

By Ohm's law for AC, Z = V / I = 240 / 12 = 20 ohms.

A continuous load draws 40 A. At what minimum ampacity must the branch-circuit conductors and overcurrent device be rated?

• a.50 A✓
• b.32 A
• c.40 A
• d.45 A

Continuous loads require 125% sizing: 40 A x 1.25 = 50 A for the conductors and overcurrent device.2023 NEC 210.20(A)

The demand factor of a system is defined as:

• a.Connected load divided by maximum demand
• b.A value always greater than 1
• c.Maximum demand divided by total connected load✓
• d.Always equal to 1

Demand factor = maximum demand / total connected load; it is 1 or less and reflects load diversity.

What are the commonly recommended maximum voltage-drop limits for a branch circuit and for the combined feeder plus branch circuit?

• a.2% and 4%
• b.3% and 5%✓
• c.5% and 8%
• d.1% and 3%

The informational recommendation is 3% maximum on a branch circuit and 5% maximum for feeder plus branch circuit combined.

For equipment operating at 0-150 V to ground under Condition 1, what is the minimum depth of working space in front of the equipment?

• a.4 ft
• b.2.5 ft
• c.2 ft
• d.3 ft✓

Condition 1 (exposed live parts on one side, no grounded parts opposite) requires a minimum working clearance of 3 ft for 0-150 V.2023 NEC 110.26(A)(1)

What is the minimum required width of working space in front of electrical equipment?

• a.36 in always
• b.24 in
• c.18 in
• d.30 in or the width of the equipment, whichever is greater✓

The working space width must be at least 30 in or the width of the equipment, whichever is greater, and must permit a 90-degree door opening.2023 NEC 110.26(A)(2)

What is the minimum headroom (height) of working space about electrical equipment such as panelboards?

• a.8 ft
• b.6 ft
• c.6.5 ft✓
• d.7 ft

The minimum headroom of working space is 6.5 ft (or the height of the equipment, whichever is greater).2023 NEC 110.26(A)(3)

The dedicated equipment space above a panelboard extends how far above the equipment (or to a structural ceiling if lower)?

• a.4.5 ft
• b.7 ft
• c.6 ft✓
• d.3 ft

The dedicated electrical space extends from the equipment to 6 ft above it, or to a structural ceiling if lower, and must be kept clear of foreign systems.2023 NEC 110.26(E)(1)

Equipment rated at what current or more requires two entrances to and egress from the working space when the space is large or contains overcurrent devices?

• a.1000 A
• b.600 A
• c.1200 A✓
• d.800 A

For equipment rated 1,200 A or more and over 6 ft wide, two entrances/egress paths to the working space are required.2023 NEC 110.26(C)(2)