Journeyman Electrician’s Exam Journeyman Electrician's Service and Feeder Calculations 3 — Questions and Answers
Question 1: A feeder supplies a motor with a 40A full-load current and a 30A continuous non-motor load. What is the minimum feeder ampacity required?
- 70 A
- 80 A
- 87.5 A (Correct answer)
- 100 A
Correct answer: 87.5 A
Motor feeder = 40A × 125% = 50A; continuous non-motor = 30A × 125% = 37.5A; total = 87.5A minimum.
Question 2: What NEC section requires that the neutral conductor of a 3-wire, single-phase service be sized to carry the maximum unbalanced load?
- NEC 220.61 (Correct answer)
- NEC 230.42
- NEC 310.15
- NEC 250.24
Correct answer: NEC 220.61
NEC 220.61 addresses feeder and service neutral load calculations including the maximum unbalanced load.
Question 3: A 240V, single-phase dryer rated at 5,000W is installed in a dwelling. What demand load does NEC 220.54 assign to a single dryer?
- 5,000 W (Correct answer)
- 5,500 W
- 4,500 W
- 4,000 W
Correct answer: 5,000 W
NEC 220.54 requires the nameplate rating or 5,000W, whichever is larger, so 5,000W applies.
Question 4: When multiple feeder conductors are installed in parallel, each conductor in the parallel set must be what minimum size?
- 1/0 AWG (Correct answer)
- 2/0 AWG
- 3/0 AWG
- 250 kcmil
Correct answer: 1/0 AWG
NEC 310.10(H) requires each parallel conductor to be a minimum of 1/0 AWG.
Question 5: A commercial occupancy has 10,000 sq ft of office space. Using NEC Table 220.12, what is the general lighting load at 3.5 VA per square foot?
- 30,000 VA
- 35,000 VA (Correct answer)
- 40,000 VA
- 45,000 VA
Correct answer: 35,000 VA
10,000 sq ft × 3.5 VA/sq ft = 35,000 VA for office general lighting.
Question 6: For dwelling unit services, NEC 220.83 (optional calculation) requires that air conditioning or heat be included at what percentage when calculating the total load?
- 65%
- 75%
- 100% (Correct answer)
- 125%
Correct answer: 100%
Under NEC 220.83, the larger of heating or cooling loads is included at 100% in the optional calculation.
Question 7: What is the calculated feeder demand for six 10 kW household electric ranges in a multi-family building per NEC Table 220.55?
- 21 kW
- 24 kW (Correct answer)
- 27 kW
- 30 kW
Correct answer: 24 kW
NEC Table 220.55 Column C assigns a demand factor of 43% for 6 ranges: 60 kW × 0.43 = 25.8, but the table directly lists 24 kW for 6 ranges.
Journeyman Electrician’s Exam Journeyman Electrician's Service and Feeder Calculations 3
A feeder supplies a motor with a 40A full-load current and a 30A continuous non-motor load.
What is the minimum feeder ampacity required?