NEC Load Calculations & Branch Circuits 3 — Questions and Answers
Question 1: For a single household electric range rated 12 kW, what is the demand load per NEC Table 220.55, Column C?
- 6 kW
- 8 kW (Correct answer)
- 10 kW
- 12 kW
Correct answer: 8 kW
Column C lists 8 kW as the demand load for one range not exceeding 12 kW.
Question 2: What demand factor may be applied to four or more fastened-in-place appliances (other than range, dryer, space-heating, A/C) in a dwelling?
- 100%
- 75% (Correct answer)
- 50%
- 25%
Correct answer: 75%
NEC 220.53 permits a 75% demand factor when four or more such appliances are on the same feeder.
Question 3: What minimum VA must be included for a household electric clothes dryer when none is specified, per NEC 220.54?
- 3000 VA
- 4000 VA
- 5000 VA (Correct answer)
- 5500 VA
Correct answer: 5000 VA
NEC 220.54 requires a minimum of 5000 VA or the nameplate rating, whichever is larger.
Question 4: When sizing a feeder for fixed electric space heating, what demand factor is generally applied to the heating load?
- 100% (Correct answer)
- 80%
- 65%
- 40%
Correct answer: 100%
Fixed electric space heating is calculated at 100% of the total connected load per NEC 220.51.
Question 5: In the standard method, when may the air-conditioning load be omitted from the service calculation?
- Never
- When smaller than the heating load (Correct answer)
- When larger than heating
- Always
Correct answer: When smaller than the heating load
NEC 220.60 allows omitting the smaller of two non-coincident loads, so A/C is dropped if it is less than the heating load.
Question 6: A dwelling has 10 kVA of fastened-in-place appliances (six units). What demand load is used?
- 10 kVA
- 7.5 kVA (Correct answer)
- 5 kVA
- 2.5 kVA
Correct answer: 7.5 kVA
With four or more appliances, the 75% factor applies: 10 kVA x 0.75 = 7.5 kVA.
Question 7: What is the minimum feeder/service conductor size requirement basis for a one-family dwelling rated 100 amperes?
- Equal to calculated load only
- Not less than service rating (Correct answer)
- Always 4 AWG
- Always 2 AWG
Correct answer: Not less than service rating
Service conductors must have an ampacity not less than the calculated load and the service rating.
NEC Load Calculations & Branch Circuits 3
For a single household electric range rated 12 kW, what is the demand load per NEC Table 220.55, Column C?