NEC Load Calculation Applications 2 — Questions and Answers
Question 1: When calculating the demand load for a commercial kitchen with six 5 kW ovens, what demand factor applies to the first 3 ovens per NEC Table 220.56?
- 100%
- 65% (Correct answer)
- 55%
- 80%
Correct answer: 65%
NEC Table 220.56 applies a 65% demand factor to the first three commercial cooking appliances when four or more units are served from the same branch circuit or feeder.
Question 2: A 200-ampere, 240-volt single-phase service supplies a dwelling. What is the net computed load in kVA that represents the full-load capacity of this service?
- 24 kVA
- 48 kVA (Correct answer)
- 40 kVA
- 200 kVA
Correct answer: 48 kVA
Net computed load = 200 A × 240 V = 48,000 VA = 48 kVA for a single-phase service.
Question 3: Under NEC 220.14(J), what is the unit load per outlet used for calculating branch-circuit loads for show-window lighting in a commercial occupancy?
- 150 VA per linear foot (Correct answer)
- 180 VA per linear foot
- 200 VA per linear foot
- 125 VA per linear foot
Correct answer: 150 VA per linear foot
NEC 220.14(J) assigns 150 VA per linear foot of show-window space for branch-circuit load calculation purposes.
Question 4: For optional calculation of a dwelling unit per NEC 220.82, which load is NOT included in the total connected load before applying demand factors?
- Electric vehicle supply equipment (Correct answer)
- Air conditioning equipment
- Lighting at 3 VA/sq ft
- Small appliance branch circuits at 1500 VA each
Correct answer: Electric vehicle supply equipment
NEC 220.82 does not include EVSE in the optional calculation; EV loads are handled separately under Article 625 and NEC 220.57.
Question 5: A 240-volt, 30-ampere dryer circuit serves a single household dryer. Per NEC 220.54, what is the minimum load to use when calculating the feeder demand for one dryer?
- 5,000 VA (Correct answer)
- 7,200 VA
- 6,000 VA
- 4,500 VA
Correct answer: 5,000 VA
NEC 220.54 requires a minimum load of 5,000 VA (or the nameplate rating if higher) for each household dryer when calculating feeder demand.
Question 6: When using the standard method to calculate a dwelling service, at what square footage threshold does the 3 VA per sq ft lighting load for the first portion end and require a different demand treatment under NEC Table 220.42?
- The entire load uses demand factors; there is no square footage threshold (Correct answer)
- 3,000 sq ft
- 2,000 sq ft
- 5,000 sq ft
Correct answer: The entire load uses demand factors; there is no square footage threshold
NEC Table 220.42 applies demand factors to the total general lighting load in VA (not square footage), with the first 3,000 VA at 100% and the remainder at 35%.
Question 7: A three-phase, 208Y/120V panel serves 12 identical 1,500 VA single-phase receptacle loads balanced across phases. What is the total three-phase feeder load before demand factors?
- 18,000 VA (Correct answer)
- 6,000 VA
- 12,000 VA
- 54,000 VA
Correct answer: 18,000 VA
Total load = 12 receptacles × 1,500 VA = 18,000 VA, which is then distributed across three phases but the total feeder VA is still 18,000 VA before demand factors.
NEC Load Calculation Applications 2
When calculating the demand load for a commercial kitchen with six 5 kW ovens, what demand factor applies to the first 3 ovens per NEC Table 220.56?