Licensed Electrical Contractor Load Calculation and Services 3 — Questions and Answers
Question 1: Per NEC 220.12, what is the general lighting load in VA per square foot for a bank?
- 1.0 VA/sq ft
- 2.0 VA/sq ft
- 3.5 VA/sq ft (Correct answer)
- 5.0 VA/sq ft
Correct answer: 3.5 VA/sq ft
NEC Table 220.12 lists banks at 3.5 VA per square foot for general lighting load calculations.
Question 2: How must the largest motor load be treated when included in a feeder or service calculation?
- Add 25% of its full-load current to the total (Correct answer)
- Use 80% of its nameplate rating
- Exclude it from the demand factor calculation
- Apply a 50% demand factor to it
Correct answer: Add 25% of its full-load current to the total
NEC 220.50 and 430.24 require adding 25% of the largest motor's full-load current to feeder demand calculations.
Question 3: A 120/240V single-phase service supplies an electric dryer rated at 5,000 W. What load is used in the standard residential calculation?
- 5,000 W
- 5,000 W or 5,000 VA, whichever is larger
- The nameplate rating or 5,000 VA, whichever is larger (Correct answer)
- 4,000 W after demand factor
Correct answer: The nameplate rating or 5,000 VA, whichever is larger
NEC 220.54 states the feeder demand for dryers is the nameplate rating or 5,000 VA, whichever is larger.
Question 4: What is the maximum number of service disconnecting means allowed for a single service?
- 2
- 4
- 6 (Correct answer)
- 8
Correct answer: 6
NEC 230.71(A) limits the service disconnecting means to a maximum of six switches or circuit breakers.
Question 5: Under the standard calculation for a 2,400 sq ft dwelling, what is the general lighting and receptacle load before demand factors (using 3 VA/sq ft)?
- 5,400 VA
- 7,200 VA (Correct answer)
- 9,600 VA
- 3,000 VA
Correct answer: 7,200 VA
2,400 sq ft × 3 VA/sq ft = 7,200 VA for general lighting and receptacle loads per NEC Table 220.12.
Question 6: The demand factor for the first 3,000 VA of a residential lighting load is:
- 50%
- 75%
- 100% (Correct answer)
- 35%
Correct answer: 100%
NEC Table 220.42 requires the first 3,000 VA of residential lighting load to be calculated at 100%.
Question 7: When computing a service load for a multi-family dwelling with 20 units, what demand factor applies to the lighting load between 3,001 VA and 120,000 VA per NEC Table 220.42?
- 100%
- 75%
- 35% (Correct answer)
- 50%
Correct answer: 35%
NEC Table 220.42 applies a 35% demand factor to the portion of dwelling lighting load between 3,001 VA and 120,000 VA.
Licensed Electrical Contractor Load Calculation and Services 3
Per NEC 220.12, what is the general lighting load in VA per square foot for a bank?