NEC Load Calculations 2 — Questions and Answers
Question 1: When calculating the load for a residential kitchen small appliance branch circuits, the NEC requires a minimum of how many 20-ampere circuits?
- One 20A circuit
- Two 20A circuits (Correct answer)
- Three 20A circuits
- One 15A and one 20A circuit
Correct answer: Two 20A circuits
NEC 210.11(C)(1) requires at least two 20-ampere small appliance branch circuits for receptacle outlets in kitchen, pantry, breakfast room, and dining room.
Question 2: For a 240V, single-phase motor rated at 10 HP, what is the full-load current used for conductor sizing per NEC Table 430.250?
- 40A
- 50A (Correct answer)
- 60A
- 28A
Correct answer: 50A
NEC Table 430.250 lists 50A as the full-load current for a 10 HP, 240V, single-phase motor.
Question 3: Under NEC Article 220, what demand factor applies to the first 3,000 VA of general lighting load in a dwelling unit?
- 35%
- 50%
- 75%
- 100% (Correct answer)
Correct answer: 100%
NEC Table 220.42 applies 100% demand factor to the first 3,000 VA of lighting load in a dwelling.
Question 4: A commercial building has 40 receptacle outlets in an office area. Using the NEC standard load calculation, what load in VA is assigned per receptacle?
- 100 VA
- 150 VA
- 180 VA (Correct answer)
- 200 VA
Correct answer: 180 VA
NEC 220.14(I) assigns 180 VA per receptacle outlet for calculating branch circuit and feeder loads in commercial occupancies.
Question 5: When calculating a feeder load for a dwelling with a 12 kW electric range, what demand value does NEC Table 220.55 allow for a single range?
- 12,000 VA
- 8,000 VA (Correct answer)
- 6,400 VA
- 9,600 VA
Correct answer: 8,000 VA
NEC Table 220.55 Column C permits 8 kW (8,000 VA) demand for a single household range rated over 8¾ kW through 12 kW.
Question 6: For optional feeder/service calculations in dwellings per NEC 220.82, the first 10 kVA of all other loads after air conditioning is applied at what demand factor?
- 40%
- 50%
- 60%
- 100% (Correct answer)
Correct answer: 100%
NEC 220.82(B) applies 100% demand factor to the first 10 kVA of all other loads in the optional calculation method.
Question 7: A 120/240V, single-phase service feeds a dwelling. The calculated load is 28,800 VA. What is the minimum service ampacity required?
- 100A
- 120A
- 150A (Correct answer)
- 200A
Correct answer: 150A
28,800 VA ÷ 240V = 120A; the next standard service size per NEC 230.79 is 150A, and residential minimum is 100A—but 120A requires 150A service.
NEC Load Calculations 2
When calculating the load for a residential kitchen small appliance branch circuits, the NEC requires a minimum of how many 20-ampere circuits?