Utah Journeyman Electrician Exam: Practice Test & Licensing Guide

A service is supplied by 3/0 AWG copper ungrounded service-entrance conductors. Using Table 250.66, what is the minimum size copper grounding electrode conductor to the metal underground water pipe electrode?

Answer: 4 AWG

Table 250.66 sizes the GEC from the largest ungrounded service-entrance conductor. The 2/0 or 3/0 AWG copper row requires a 4 AWG copper GEC. 6 AWG is the row for 1 or 1/0 AWG, and 2 AWG applies only above 3/0 through 350 kcmil. The 250.66(A) 6 AWG limit applies only to the part of a GEC that is the sole connection to a rod, pipe or plate electrode, not to a water pipe electrode.

Reference: NFPA 70, National Electrical Code, 2023, 250.66 and Table 250.66

Using Table 250.122, what is the minimum size copper equipment grounding conductor for a branch circuit protected by a 60-ampere circuit breaker?

Answer: 10 AWG

Table 250.122 sizes the EGC by the rating of the overcurrent device ahead of the circuit, not by the circuit's conductors. The 60 A row requires 10 AWG copper. 8 AWG is the row for 100 A, and 12 AWG covers only up to 20 A. Remember the EGC may need to be upsized if the ungrounded conductors are increased for voltage drop (250.122(B)).

Reference: NFPA 70, National Electrical Code, 2023, Table 250.122

Unless specifically permitted elsewhere in the Code, what is the maximum overcurrent protection for 12 AWG copper conductors?

Answer: 20 A

Section 240.4(D) limits small conductors: 14 AWG copper to 15 A, 12 AWG copper to 20 A, and 10 AWG copper to 30 A. This applies after any correction and adjustment factors. Although Table 310.16 lists 12 AWG copper at 25 A (75°C) or 30 A (90°C), the 240.4(D) limit controls the overcurrent device.

Reference: NFPA 70, National Electrical Code, 2023, 240.4(D)

A branch circuit supplies 24 A of continuous load and 10 A of noncontinuous load. What is the minimum standard-size overcurrent device permitted by 210.20(A)?

Answer: 40 A

Section 210.20(A) requires the OCPD rating to be at least 100% of the noncontinuous load plus 125% of the continuous load. 10 + (24 x 1.25) = 10 + 30 = 40 A, and 40 A is a standard size in 240.6(A). 35 A is the result if you don't apply the 125% factor (34 A rounded up). 45 A comes from applying 125% to the whole 34 A (42.5 A).

Reference: NFPA 70, National Electrical Code, 2023, 210.20(A)

A 120/240-volt overhead service drop passes over a residential driveway. What is the minimum clearance above the driveway?

Answer: 12 ft

Section 230.24(B)(2) requires 12 ft over residential property and driveways where the voltage does not exceed 300 V to ground. A 120/240 V system is 120 V to ground. 10 ft applies only over areas accessible to pedestrians only (150 V to ground or less). 18 ft is for public streets, alleys, roads and parking areas subject to truck traffic.

Reference: NFPA 70, National Electrical Code, 2023, 230.24(B)(2)

Six current-carrying 12 AWG copper THHN conductors are installed in one raceway at 30°C (86°F) ambient. Starting from the 90°C column of Table 310.16, what is the adjusted ampacity of each conductor?

Answer: 24 A

12 AWG THHN is 30 A in the 90°C column of Table 310.16. Table 310.15(C)(1) requires an 80% adjustment for 4-6 current-carrying conductors: 30 x 0.80 = 24 A. No ambient correction applies at 30°C. The overcurrent device is still limited to 20 A by 240.4(D), but the adjusted ampacity itself is 24 A. 25 A is the unadjusted 75°C value.

Reference: NFPA 70, National Electrical Code, 2023, Table 310.16 and Table 310.15(C)(1)

A surface-mounted LED luminaire with a completely enclosed light source is installed on the ceiling of a clothes closet. What is the minimum clearance between the luminaire and the nearest point of the storage space?

Answer: 12 in.

Section 410.16(C)(1) permits surface-mounted incandescent or LED luminaires with a completely enclosed light source on the wall above the door or on the ceiling if 12 in. of clearance to the storage space is kept. 6 in. is the clearance for recessed luminaires with enclosed light sources and for surface-mounted fluorescent luminaires (410.16(C)(2) through (C)(4)).

Reference: NFPA 70, National Electrical Code, 2023, 410.16(C)(1)

A metal device box contains a receptacle, two 12/2 NM cables with ground (four insulated 12 AWG conductors and two bare 12 AWG EGCs), and internal cable clamps. Using 314.16(B) and Table 314.16(B), what minimum box volume is required?

Answer: 18.0 in.3

Conductor count under 314.16(B): 4 insulated conductors = 4. All EGCs together = 1. Internal clamps (one or more) = 1. The receptacle yoke = 2. The total is 8 conductor volumes. Table 314.16(B) allows 2.25 in.3 for each 12 AWG, so 8 x 2.25 = 18.0 in.3. 15.75 in.3 (7 volumes) forgets the clamps. 20.25 in.3 (9) counts each EGC separately. 13.5 in.3 (6) leaves out both the EGCs and the clamps.

Reference: NFPA 70, National Electrical Code, 2023, 314.16(B) and Table 314.16(B)

A 120-volt single-phase branch circuit uses 12 AWG copper (6,530 circular mils). It carries 16 A to a load 100 ft away. Using VD = 2KIL/CM with K = 12.9, what is the approximate voltage drop?

Answer: 6.3 V

VD = 2 x K x I x L / CM = 2 x 12.9 x 16 x 100 / 6,530 = 41,280 / 6,530 = 6.32 V. L is the one-way length, and the 2 accounts for current flowing out and back. 3.2 V leaves out the 2, and 5.3 V is the drop expressed as a percentage (6.32 / 120 = 5.3%), not in volts. Circular mils come from NEC Chapter 9, Table 8.

Reference: Ugly's Electrical References, 2023, Voltage drop, single-phase: VD = 2KIL/CM

A 15-kW, 208-volt, three-phase resistive heater is installed. What line current does it draw?

Answer: 41.6 A

For three-phase loads, I = P / (E x 1.732) = 15,000 / (208 x 1.732) = 15,000 / 360.3 = 41.6 A. 72.1 A leaves out the 1.732 (single-phase formula), 24.0 A divides by 3 instead of 1.732, and 36.1 A uses 240 V.

Reference: Ugly's Electrical References, 2023, Three-phase current: I = P / (E x 1.732)