Master Electrician (NEC) — All Questions

What is the maximum number of service disconnecting means permitted for a single set of service-entrance conductors (each in a separate enclosure)?

• a.Eight
• b.Six✓
• c.One
• d.Four

A service is limited to a maximum of six disconnecting means. In the 2023 NEC each of the up-to-six disconnects must be in a separate enclosure or be part of listed equipment.2023 NEC 230.71

A service uses #2/0 Cu ungrounded conductors. What is the minimum copper grounding electrode conductor?

• a.#4 AWG✓
• b.#2 AWG
• c.#8 AWG
• d.#6 AWG

For service conductors over 1/0 through 3/0 Cu, the table requires a #4 Cu grounding electrode conductor.2023 NEC Table 250.66

Where the grounding electrode conductor connects only to a made ground rod, what is the largest copper conductor size ever required?

• a.#4 AWG
• b.#6 AWG✓
• c.#8 AWG
• d.#2 AWG

The portion of the GEC connecting solely to a rod, pipe, or plate electrode need not be larger than #6 Cu.2023 NEC 250.66(A)

A branch circuit is protected by a 100-A overcurrent device. What is the minimum copper equipment grounding conductor?

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

The equipment grounding conductor table requires #8 Cu for an overcurrent device rating up to 100 A.2023 NEC Table 250.122

A feeder is protected by a 400-A overcurrent device. What is the minimum copper equipment grounding conductor?

• a.#6 AWG
• b.#4 AWG
• c.#1 AWG
• d.#3 AWG✓

For a 400-A overcurrent device the table requires #3 Cu for the equipment grounding conductor.2023 NEC Table 250.122

A service has 500-kcmil Cu ungrounded conductors per phase. What is the minimum copper grounded (neutral) service conductor for bonding purposes?

• a.1/0 AWG✓
• b.#1 AWG
• c.#2 AWG
• d.#4 AWG

The grounded service conductor must be at least the size in Table 250.102(C)(1); for 500-kcmil Cu phase conductors that value is 1/0 Cu.2023 NEC Table 250.102(C)(1)

Service phase conductors total 1,500 kcmil Cu per phase (over 1,100 kcmil). Using the 12.5% rule, what is the minimum copper main bonding jumper?

• a.4/0 AWG✓
• b.250 kcmil
• c.2/0 AWG
• d.3/0 AWG

Above 1,100 kcmil, the main bonding jumper is at least 12.5% of the phase area: 0.125 x 1,500 = 187.5 kcmil, so 4/0 Cu (211.6 kcmil) is the smallest that qualifies.2023 NEC 250.28(D)

A panelboard is rated 225 A. What is the maximum rating of the overcurrent device that may protect it?

• a.225 A✓
• b.200 A
• c.400 A
• d.250 A

Each panelboard must be protected by an overcurrent device rated no more than the panelboard rating, so 225 A is the maximum.2023 NEC 408.36

Which of the following is the next standard overcurrent device rating above 95 A?

• a.90 A
• b.125 A
• c.110 A
• d.100 A✓

Standard ratings include 90, 100, 110, and 125 A. The next standard size above 95 A is 100 A.2023 NEC 240.6

Absent a specific exception, what is the maximum overcurrent protection for a #12 Cu conductor?

• a.20 A✓
• b.25 A
• c.30 A
• d.15 A

Under the small-conductor rule, #12 Cu is limited to a maximum overcurrent device of 20 A.2023 NEC 240.4(D)

Absent a specific exception, what is the maximum overcurrent protection for a #10 Cu conductor?

• a.25 A
• b.40 A
• c.30 A✓
• d.20 A

The small-conductor rule limits #10 Cu to a maximum 30-A overcurrent device.2023 NEC 240.4(D)

A conductor has an allowable ampacity of 115 A, which is not a standard rating. Under the next-standard-size rule (600 A or less), what is the largest permitted overcurrent device?

• a.125 A✓
• b.100 A
• c.110 A
• d.150 A

When ampacity does not match a standard rating and conditions are met, the next higher standard device (125 A) is permitted for 800-A or smaller circuits.2023 NEC 240.4(B)

What is the smallest conductor size generally permitted to be installed in parallel?

• a.1/0 AWG✓
• b.#1 AWG
• c.2/0 AWG
• d.#2 AWG

Conductors are generally permitted in parallel only in sizes 1/0 AWG and larger.2023 NEC 310.10(G)

Two paralleled sets of 500-kcmil Cu (75 C, 380 A each) supply one feeder. What is the combined ampacity before adjustment?

• a.620 A
• b.760 A✓
• c.380 A
• d.500 A

Paralleled conductor ampacities add: 380 A x 2 = 760 A total for the feeder.2023 NEC Table 310.16

What is the minimum service disconnecting-means rating for a one-family dwelling?

• a.200 A
• b.125 A
• c.60 A
• d.100 A✓

The service disconnecting means for a one-family dwelling must be rated at least 100 A, 3-wire.2023 NEC 230.79

What is the minimum vertical clearance for an overhead service drop, not over 300 V to ground, above a residential driveway that is not subject to truck traffic?

• a.15 ft
• b.12 ft✓
• c.10 ft
• d.18 ft

Service-drop conductors up to 300 V to ground require 12 ft of clearance over residential property and driveways not subject to truck traffic.2023 NEC 230.24(B)

At a separately derived system such as a transformer, what conductor connects the grounded conductor to the system grounding electrode?

• a.Equipment bonding jumper
• b.Main bonding jumper
• c.Grounding electrode conductor✓
• d.System bonding jumper

Per 2023 NEC 250.30(A)(5), the grounding electrode conductor connects the grounded conductor of a separately derived system to the grounding electrode. Trap: the system bonding jumper (250.30(A)(1)) bonds the grounded conductor to the equipment/enclosure, not to the electrode.2023 NEC 250.30(A)(5)

An emergency system must be capable of supplying power to its loads within what maximum time after normal supply is lost?

• a.120 seconds
• b.10 seconds✓
• c.60 seconds
• d.30 seconds

Emergency systems must restore power to life-safety loads within 10 seconds of loss of the normal source.2023 NEC 700.12

A legally required standby system must supply its loads within what maximum time after loss of normal power?

• a.30 seconds
• b.10 seconds
• c.60 seconds✓
• d.120 seconds

Legally required standby systems must be able to supply their loads within 60 seconds of a normal-source failure.2023 NEC 701.12

Generator output conductors must have an ampacity of at least what percent of the nameplate current?

• a.100%
• b.125%
• c.110%
• d.115%✓

Generator conductors from the terminals to the first overcurrent device must be at least 115% of the nameplate current rating.2023 NEC 445.13

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 transformer (separately derived system) has 3/0 AWG copper derived (secondary) phase conductors. What is the minimum copper grounding electrode conductor for the SDS?

• a.#6 AWG
• b.#2 AWG
• c.#1 AWG
• d.#4 AWG✓

2023 NEC 250.30(A)(5) sizes the SDS grounding electrode conductor from Table 250.66 using the derived phase conductors: 2/0-3/0 Cu requires #4 Cu. Trap: #6 is the maximum only when the GEC connects solely to a rod, pipe, or plate, not for the transformer GEC to building steel or water pipe.2023 NEC 250.30(A)(5)

A separately derived system has 250-kcmil copper derived conductors. Using the bonding table, what is the minimum copper system/supply-side bonding jumper?

• a.#2 AWG✓
• b.#4 AWG
• c.#1 AWG
• d.1/0 AWG

2023 NEC 250.30(A)(2) with Table 250.102(C)(1): over 3/0 through 350 kcmil Cu requires a #2 Cu bonding jumper. Trap: #4 is the value for 2/0-3/0 Cu, one row too small for 250 kcmil.2023 NEC 250.102(C)(1)

Overcurrent devices in an emergency system (Article 700) that supply life-safety loads must be:

• a.series rated only
• b.all the same ampere rating
• c.selectively coordinated✓
• d.ganged together

2023 NEC 700.32 requires emergency-system OCPDs to be selectively coordinated with all supply-side devices so that a downstream fault opens only the nearest device. Trap: series rating addresses interrupting capacity, not coordination of tripping.2023 NEC 700.32

A 400-A feeder is run as two parallel sets in separate metal raceways. What size copper equipment grounding conductor is required in each raceway?

• a.#6 AWG, half in each raceway
• b.#3 AWG in each raceway✓
• c.a single #3 AWG total
• d.#8 AWG in each raceway

2023 NEC 250.122(F) requires a full-size EGC in each raceway sized to the 400-A device; Table 250.122 gives #3 Cu for 400 A, so each raceway carries a full #3 Cu. Trap: the EGC is never divided between the parallel raceways.2023 NEC 250.122(F)

Service-entrance conductors supply a 200-A continuous load. What minimum conductor ampacity is required?

• a.160 A
• b.200 A
• c.230 A
• d.250 A✓

2023 NEC 230.42(A) requires the service conductors to carry 125% of the continuous load: 200 x 1.25 = 250 A. Trap: 200 A ignores the continuous-load multiplier.2023 NEC 230.42(A)

A service has 500-kcmil copper ungrounded conductors. What is the minimum copper bonding jumper for the metal underground water pipe?

• a.1/0 AWG✓
• b.#2 AWG
• c.#4 AWG
• d.#3 AWG

2023 NEC 250.104(A)(1) sizes the water-pipe bonding jumper from Table 250.66: over 350 through 600 kcmil Cu requires 1/0 Cu. Trap: #2 is the value for 250-350 kcmil, one row too small for 500 kcmil.2023 NEC 250.104(A)

Under 110.9, a circuit breaker or fuse intended to interrupt fault current must have an interrupting rating that is:

• a.equal to the load current
• b.125% of the continuous load
• c.at least the available fault current at its 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. Trap: ampacity and load current size the device for normal operation, not for interrupting a fault.2023 NEC 110.9

A downstream circuit breaker has an interrupting rating below the available fault current. It may still be applied if:

• a.it is derated 20% for continuous-duty operation inside a sealed enclosure
• b.it is part of a listed, tested series combination with the line-side device✓
• c.it is a molded-case type
• d.the connected load is noncontinuous

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). Trap: derating a breaker does not raise its interrupting (fault) rating.2023 NEC 240.86

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.