IEC Service and Load Calculations 2 — Questions and Answers
Question 1: When calculating the demand load for a residential range rated at 12 kW, what demand factor does NEC Table 220.55 apply for a single range?
- 80%
- 100%
- 8 kW (Column C value) (Correct answer)
- 70%
Correct answer: 8 kW (Column C value)
NEC Table 220.55, Column C assigns 8 kW demand for a single household cooking appliance rated 12 kW or less.
Question 2: A 200-ampere, 240-volt single-phase service has a calculated load of 180 amperes. What is the demand factor for this service?
- 80%
- 90% (Correct answer)
- 100%
- 75%
Correct answer: 90%
Demand factor = actual load ÷ connected load = 180 A ÷ 200 A = 90%.
Question 3: For a commercial occupancy, NEC 220.42 allows a demand factor of 50% on lighting loads exceeding how many volt-amperes?
- 20,000 VA (Correct answer)
- 50,000 VA
- 3,000 VA
- 10,000 VA
Correct answer: 20,000 VA
NEC Table 220.42 permits a 50% demand factor on the portion of the lighting load above 20,000 VA for certain commercial spaces.
Question 4: What minimum ampacity service is required for a one-family dwelling under NEC 230.79(C)?
- 60 amperes
- 100 amperes (Correct answer)
- 150 amperes
- 200 amperes
Correct answer: 100 amperes
NEC 230.79(C) requires a minimum 100-ampere, 3-wire service for one-family dwellings.
Question 5: A dwelling has 3,500 sq ft of living space. Using NEC 220.12, what is the general lighting load at 3 VA per sq ft?
- 8,000 VA
- 10,500 VA (Correct answer)
- 7,000 VA
- 12,000 VA
Correct answer: 10,500 VA
3,500 sq ft × 3 VA/sq ft = 10,500 VA for general lighting and receptacle loads.
Question 6: When sizing a service for a multiunit apartment building, NEC 220.84 permits the use of which calculation method as an alternative to the standard method?
- Optional calculation method
- Feeder calculation method
- Optional method for multi-family dwellings (Correct answer)
- Demand factor method only
Correct answer: Optional method for multi-family dwellings
NEC 220.84 provides an optional calculation method for multi-family dwellings using Table 220.84 demand factors.
Question 7: For fixed electric space heating, NEC 220.51 requires that heating loads be calculated at what percentage of the total connected load?
- 65%
- 80%
- 100% (Correct answer)
- 125%
Correct answer: 100%
NEC 220.51 requires fixed electric space heating to be calculated at 100% of the total connected load with no demand factor reduction.
IEC Service and Load Calculations 2
When calculating the demand load for a residential range rated at 12 kW, what demand factor does NEC Table 220.55 apply for a single range?