Master Electrician (NEC) — All Questions

For a circuit rated 100 A or less, conductor ampacity is generally based on which temperature column unless the equipment is listed otherwise?

• a.90 C
• b.75 C
• c.105 C
• d.60 C✓

Terminations on equipment rated 100 A or less are based on the 60 C column unless the equipment and conductors are listed for a higher temperature.2023 NEC 110.14(C)(1)

For circuits rated over 100 A, conductor ampacity for terminations is generally based on which temperature column?

• a.Nameplate only
• b.90 C
• c.75 C✓
• d.60 C

Terminations on equipment over 100 A are based on the 75 C column unless listed and marked for a higher rating.2023 NEC 110.14(C)(1)

Which standard governs electrical safety-related work practices, including arc-flash and shock protection?

• a.OSHA 1910 only
• b.NFPA 70E✓
• c.NFPA 72
• d.NEC (NFPA 70)

NFPA 70E, Standard for Electrical Safety in the Workplace, covers safe work practices, arc-flash boundaries, and PPE selection.

Under safe electrical work practices, what is the preferred condition before working on or near exposed conductors?

• a.Energized with a permit
• b.An electrically safe (de-energized and verified) work condition✓
• c.Wearing rubber gloves
• d.Under observation

The safest and preferred approach is to place equipment in an electrically safe work condition: de-energize, lock out, and verify absence of voltage before work.

What is the primary purpose of a lockout/tagout (LOTO) procedure under Cal/OSHA?

• a.To install ground rods
• b.To label panel directories
• c.To test GFCI devices
• d.To isolate and control hazardous energy during servicing✓

LOTO isolates and controls hazardous energy sources so equipment cannot be re-energized while workers are servicing it.

During electrical construction, a rough-in (rough) inspection is generally performed:

• a.After the final inspection
• b.After energizing the system
• c.Before wiring is concealed or covered✓
• d.Only at final occupancy

The rough inspection occurs after wiring is installed but before walls or wiring are covered, so the inspector can verify concealed work.

Who is responsible for interpreting and enforcing the requirements of the NEC?

• a.The authority having jurisdiction (AHJ)✓
• b.The serving utility
• c.The NFPA
• d.The equipment manufacturer

The authority having jurisdiction enforces the Code, makes interpretations, and grants any special permission where allowed.2023 NEC 90.4

The NEC generally does not cover which of the following installations?

• a.Dwelling branch circuits
• b.Utility-owned generation and distribution under exclusive utility control✓
• c.Commercial feeders
• d.Industrial services

The Code does not apply to installations under the exclusive control of an electric utility for generation, transmission, or distribution of power.2023 NEC 90.2(B)

Service equipment (other than dwellings) must be field marked with what value related to fault protection?

• a.Maximum available fault current✓
• b.Phase rotation
• c.Installation date only
• d.The panel interrupting rating only

Service equipment must be legibly field marked with the maximum available fault current and the date of the calculation.2023 NEC 110.24(A)

Equipment likely to be examined or serviced while energized must carry what type of field-applied marking?

• a.Voltage rating only
• b.Phase-sequence label
• c.An arc-flash hazard warning label✓
• d.Equipment grounding conductor size

An arc-flash warning label must be applied to warn qualified persons of the potential arc-flash hazard before energized examination or servicing.2023 NEC 110.16

A one-family dwelling has a total general load (lighting, small-appliance, laundry, fastened appliances, ranges) of 40,000 VA before HVAC. Using the optional method of 220.82(B), what is the demand for these general loads?

• a.22,000 VA✓
• b.16,000 VA
• c.40,000 VA
• d.28,000 VA

2023 NEC 220.82(B) takes 100% of the first 10 kVA plus 40% of the remainder: 10,000 + 0.40 x 30,000 = 10,000 + 12,000 = 22,000 VA. Trap: 16,000 VA applies 40% to the whole 40,000; the first 10 kVA must stay at 100%.2023 NEC 220.82(B)

Under the optional dwelling calculation, central electric space-heating load is included at what percent of nameplate?

• a.100%
• b.65%✓
• c.40%
• d.75%

2023 NEC 220.82(C)(3) permits central electric space heating at 65% of nameplate. Trap: the 40% figure (220.82(C)(5)) applies only to four or more separately controlled electric-heat units, not to central heat.2023 NEC 220.82(C)

A 10,000 sq ft office building is calculated for general lighting using the 2023 unit-load table for office/bank occupancies. What is the general lighting load?

• a.25,000 VA
• b.20,000 VA
• c.30,000 VA
• d.35,000 VA✓

2023 NEC Table 220.42(A) lists 3.5 VA per sq ft for banks and office buildings: 10,000 x 3.5 = 35,000 VA. Trap: 30,000 VA uses the 3 VA/sq ft dwelling/store value.2023 NEC Table 220.42(A)

A 6,000 sq ft retail store is calculated for general lighting using the 2023 unit-load table. What is the general lighting load?

• a.18,000 VA✓
• b.12,000 VA
• c.21,000 VA
• d.15,000 VA

2023 NEC Table 220.42(A) lists 3 VA per sq ft for stores: 6,000 x 3 = 18,000 VA. Trap: 21,000 VA mistakenly uses the 3.5 VA/sq ft office value.2023 NEC Table 220.42(A)

A commercial service supplies several motors; the largest has a 40-A full-load current. How much is added to the service calculation for the largest-motor factor?

• a.50 A
• b.40 A
• c.10 A✓
• d.8 A

2023 NEC 430.24 (with 220.50) requires 25% of the largest motor FLC be added on top of the motor loads: 0.25 x 40 = 10 A. Trap: 50 A adds 125% of the motor, double-counting the FLC that is already in the load.2023 NEC 430.24

A commercial kitchen has six kitchen-equipment units totaling 60 kW. Applying the demand factor for six or more units, what is the demand load?

• a.60 kW
• b.39 kW✓
• c.45 kW
• d.42 kW

2023 NEC Table 220.56 allows 65% for six or more units: 60 x 0.65 = 39 kW (result may not be less than the sum of the two largest units). Trap: 45 kW uses 75%, the four-appliance dwelling factor, not the commercial-kitchen table.2023 NEC 220.56

Transformer secondary conductors run 8 ft to a panelboard under the 10-ft secondary rule. Their ampacity must be not less than:

• a.10% of the primary overcurrent device rating
• b.the primary conductor ampacity
• c.the rating of the device or busbar they supply✓
• d.at least 300% of the transformer's rated secondary current

2023 NEC 240.21(C)(2) allows unprotected secondary conductors up to 10 ft if their ampacity is at least the calculated load and at least the rating of the device or busbar they terminate in. Trap: the 1/10 rule belongs to the 10-ft feeder tap 240.21(B)(1), not the transformer-secondary rule.2023 NEC 240.21(C)(2)

A 75-kVA, 480-208Y/120-V transformer feeds a panel through 20-ft secondary conductors under 240.21(C)(6). What is the minimum secondary conductor ampacity?

• a.208 A✓
• b.167 A
• c.260 A
• d.104 A

Secondary FLC = 75,000 / (1.732 x 208) = 208 A. 240.21(C)(6) requires the 20-ft secondary conductors to have ampacity at least equal to the transformer secondary current (208 A) and to terminate in a single OCPD not exceeding that ampacity. Trap: 260 A is 125% of secondary current, which would size the OCPD, not the minimum conductor.2023 NEC 240.21(C)(6)

A 400-A feeder overcurrent device supplies a 10-ft tap. Under the 10-ft feeder tap rule, what minimum tap-conductor ampacity comes from the 1/10 provision?

• a.200 A
• b.133 A
• c.13 A
• d.40 A✓

2023 NEC 240.21(B)(1) requires the 10-ft tap ampacity to be at least 1/10 of the 400-A device: 400 / 10 = 40 A (and at least the load served). Trap: 133 A is the 1/3 value that belongs to the 25-ft tap rule 240.21(B)(2).2023 NEC 240.21(B)(1)

A 600-A feeder overcurrent device supplies a 25-ft tap. Under the 25-ft feeder tap rule, what minimum tap-conductor ampacity is required?

• a.60 A
• b.200 A✓
• c.300 A
• d.150 A

2023 NEC 240.21(B)(2) requires the 25-ft tap ampacity to be at least 1/3 of the 600-A device: 600 / 3 = 200 A. Trap: 60 A applies the 1/10 rule, which is only for the 10-ft tap.2023 NEC 240.21(B)(2)

A 75-kVA transformer with a 208-A secondary (over 9 A) is protected on both the primary and the secondary. What is the maximum secondary overcurrent device (next higher standard permitted)?

• a.300 A✓
• b.260 A
• c.250 A
• d.225 A

Table 450.3(B) allows up to 125% on the secondary where both sides are protected: 208 x 1.25 = 260 A. Since 260 A is not a standard size, Note 1 permits the next higher standard rating, 300 A. Trap: 250 A is the next lower standard and would be too small to carry full secondary load.2023 NEC 450.3(B)

From the motor full-load current table, what is the full-load current of a 50-HP, 460-V, three-phase induction motor?

• a.52 A
• b.80 A
• c.65 A✓
• d.48 A

2023 NEC Table 430.250 lists 65 A for a 50-HP, 460-V three-phase motor. This table FLC (not nameplate) is used for branch-circuit and feeder sizing. Trap: 52 A is the 40-HP value.2023 NEC Table 430.250

A motor with a 34-A full-load current is protected by a non-time-delay (one-time) fuse. At 300%, what is the maximum branch-circuit short-circuit/ground-fault fuse (next standard size)?

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

Table 430.52 allows 300% for non-time-delay fuses: 34 x 3.00 = 102 A. Where this is not a standard size, 430.52(C)(1) Exception 1 permits the next higher standard fuse, 110 A. Trap: a time-delay (dual-element) fuse uses only 175% (60 A).2023 NEC 430.52

The optional calculation for a multifamily dwelling (220.84) may be used only where the building has at least how many dwelling units?

• a.3✓
• b.2
• c.5
• d.10

2023 NEC 220.84 applies to multifamily dwellings of three or more units that meet the stated conditions (single feeder per unit, electric cooking, and electric heat or air-conditioning). Trap: 5 confuses this with range-table diversity, not the unit-count threshold.2023 NEC 220.84

A feeder supplies five household electric ranges, each rated 12 kW. Using Column C of the range demand table, what is the demand load?

• a.17,000 VA
• b.25,000 VA
• c.20,000 VA✓
• d.21,000 VA

2023 NEC Table 220.55, Column C, gives 20 kW for five ranges not over 12 kW: 20,000 VA. Trap: 21,000 VA is the six-range value; 25,000 VA wrongly prorates 5 x 5 kW.2023 NEC Table 220.55

A service neutral carries a maximum unbalanced load of 250 A. Applying the neutral demand allowance, what is the calculated neutral load?

• a.250 A
• b.235 A✓
• c.225 A
• d.210 A

2023 NEC 220.61(B) permits 70% on the portion of neutral load over 200 A: 200 + 0.70 x 50 = 200 + 35 = 235 A. Trap: 250 A ignores the reduction; only the amount above 200 A is reduced.2023 NEC 220.61(B)

When more than two conductors are pulled into a single conduit, what maximum percent of the conduit's cross-sectional area may they occupy?

• a.53%
• b.31%
• c.60%
• d.40%✓

2023 NEC Chapter 9, Table 1: over two conductors is limited to 40% fill. Trap: 53% is the limit for one conductor and 31% for exactly two.2023 NEC Chapter 9 Table 1

A box contains eight #12 AWG conductors and nothing else. Using the box-fill volume allowance, what minimum box volume is required?

• a.16.0 cu in
• b.20.0 cu in
• c.18.0 cu in✓
• d.22.5 cu in

2023 NEC Table 314.16(B) assigns 2.25 cu in to each #12 conductor: 8 x 2.25 = 18.0 cu in. Trap: 16.0 uses the 2.0 cu in #14 value; 22.5 uses the 2.5 cu in #10 value.2023 NEC Table 314.16(B)

Under the optional method for adding load to an existing dwelling (220.83), after taking 100% of the first 8 kVA, the remaining other loads are calculated at what percent?

• a.40%✓
• b.35%
• c.50%
• d.65%

2023 NEC 220.83(B) takes 100% of the first 8 kVA and 40% of the remainder of the other load where additional air-conditioning or space-heating is being added. Trap: 35% is the general-lighting remainder factor from the standard method 220.42, not 220.83.2023 NEC 220.83(B)

A large multifamily building has 900,000 VA of connected load and an applicable 220.84 demand factor of 32%. What is the calculated demand load?

• a.450,000 VA
• b.900,000 VA
• c.288,000 VA✓
• d.360,000 VA

The optional multifamily method multiplies connected load by the Table 220.84 demand factor: 900,000 x 0.32 = 288,000 VA. Trap: 360,000 VA uses 40%; the demand factor falls as the number of units rises.2023 NEC 220.84

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

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

What three-phase transformer kVA rating corresponds to a full-load current of 100 A at 480 V?

• a.48 kVA
• b.144 kVA
• c.83 kVA✓
• d.100 kVA

kVA = (1.732 x V x I) / 1000 = (1.732 x 480 x 100) / 1000 = 83.1 kVA. Trap: 48 kVA omits the 1.732 three-phase factor.

A single-phase load draws 30 A at 240 V with a 0.90 power factor. What is the real power?

• a.7,200 W
• b.6,480 W✓
• c.5,760 W
• d.6,000 W

P = V x I x PF = 240 x 30 x 0.90 = 6,480 W. Trap: 7,200 W is the apparent power (VA) before power factor is applied.

A resistive heating element carries 10 A and has a resistance of 2 ohms. What power does it dissipate?

• a.20 W
• b.40 W
• c.100 W
• d.200 W✓

P = I^2 x R = 10^2 x 2 = 100 x 2 = 200 W. Trap: 20 W multiplies I x R, which gives the voltage drop (20 V), not power.

A motor delivers 10 HP of mechanical output while drawing 8,300 W of electrical input. What is its approximate efficiency?

• a.90%✓
• b.85%
• c.80%
• d.75%

10 HP = 7,460 W of output (746 W/HP). Efficiency = output / input = 7,460 / 8,300 = 0.90 = 90%. Trap: 75% forgets to convert HP to watts.

Equipment operating at 151-600 V to ground under Condition 3 requires what minimum depth of working space?

• a.3 ft
• b.3.5 ft
• c.4 ft✓
• d.5 ft

2023 NEC Table 110.26(A)(1): for 151-600 V, Condition 3 (exposed live parts on both sides of the working space) requires 4 ft. Trap: 3 ft is the Condition 1 value at this voltage.2023 NEC Table 110.26(A)(1)

Equipment that is listed or labeled must be installed and used:

• a.entirely at the discretion of the installing electrician on the job site
• b.per any instructions included in its listing or labeling✓
• c.only by the original manufacturer
• d.without regard to the product label

2023 NEC 110.3(B) requires listed or labeled equipment to be installed and used in accordance with any instructions included in the listing or labeling. Trap: field practice cannot override the listing instructions.2023 NEC 110.3(B)