NEC Load Calculation Applications 3 — Questions and Answers
Question 1: Per NEC 220.12, what is the minimum general illumination load in VA per square foot for a hospital?
- 2 VA/sq ft (Correct answer)
- 3 VA/sq ft
- 1 VA/sq ft
- 3.5 VA/sq ft
Correct answer: 2 VA/sq ft
NEC Table 220.12 lists hospitals at 2 VA per square foot for the general lighting load calculation.
Question 2: When calculating feeder load for fixed electric space heating under NEC 220.51, what percentage of the total connected heating load must be used?
- 100% (Correct answer)
- 75%
- 65%
- 80%
Correct answer: 100%
NEC 220.51 requires that 100% of the total connected fixed electric space heating load be included in feeder calculations with no demand factor reduction.
Question 3: A 400-ampere, 208Y/120V, three-phase service is installed. What is the calculated kVA capacity of this service?
- 144 kVA (Correct answer)
- 83.2 kVA
- 48 kVA
- 166.4 kVA
Correct answer: 144 kVA
Three-phase kVA = √3 × 208 V × 400 A ÷ 1000 = 1.732 × 208 × 400 ÷ 1000 ≈ 144 kVA.
Question 4: Under NEC 220.55, how many household cooking units must be on a single feeder before demand factors from Table 220.55 can be applied?
- Two or more (Correct answer)
- Four or more
- Three or more
- Five or more
Correct answer: Two or more
NEC 220.55 allows demand factors from Table 220.55 to be applied when two or more single-phase household ranges are supplied by a three-phase feeder.
Question 5: What NEC section governs the calculation of feeder loads for marinas and boatyards?
- 553.12 (Correct answer)
- 220.60
- 230.42
- 550.18
Correct answer: 553.12
NEC 553.12 provides the specific feeder and service load calculation requirements for floating buildings and marina receptacle loads.
Question 6: Per NEC 220.43(A), what load in VA per linear foot is assigned to fixed multioutlet assemblies when appliances are likely to be used simultaneously?
- 180 VA per linear foot (Correct answer)
- 150 VA per linear foot
- 90 VA per linear foot
- 200 VA per linear foot
Correct answer: 180 VA per linear foot
NEC 220.43(A) assigns 180 VA per linear foot for fixed multioutlet assemblies in areas where appliances will be used simultaneously.
Question 7: When calculating the demand load for a dwelling unit with a 12 kW range using NEC Table 220.55, what is the maximum demand allowed for a single range up to 12 kW?
- 8,000 W (Correct answer)
- 12,000 W
- 10,000 W
- 6,500 W
Correct answer: 8,000 W
Per NEC Table 220.55, Column C, the maximum demand for a single range rated up to 12 kW is 8,000 W (8 kW).
NEC Load Calculation Applications 3
Per NEC 220.12, what is the minimum general illumination load in VA per square foot for a hospital?