IEC Service and Load Calculations 3 — Questions and Answers
Question 1: A 240-volt, 30-ampere clothes dryer circuit is installed in a dwelling. What minimum load must be used for service calculation per NEC 220.54?
- 5,000 VA (Correct answer)
- 7,200 VA
- 4,500 VA
- 3,000 VA
Correct answer: 5,000 VA
NEC 220.54 requires each dryer to be calculated at 5,000 watts or the nameplate rating, whichever is larger.
Question 2: In a standard residential load calculation, small appliance branch circuit loads are added at what VA per circuit?
- 1,200 VA
- 1,500 VA (Correct answer)
- 1,800 VA
- 2,000 VA
Correct answer: 1,500 VA
NEC 220.52(A) requires 1,500 VA per 20-ampere small appliance branch circuit in the kitchen, dining, and pantry areas.
Question 3: What is the NEC-required number of minimum small appliance branch circuits for a dwelling unit kitchen?
- One 20-ampere circuit
- Two 20-ampere circuits (Correct answer)
- Three 20-ampere circuits
- One 15-ampere circuit
Correct answer: Two 20-ampere circuits
NEC 210.11(C)(1) requires at least two 20-ampere small appliance branch circuits for the kitchen, dining, and pantry areas.
Question 4: When calculating the service load for four household clothes dryers in an apartment building, what demand factor does NEC Table 220.54 apply?
- 100%
- 85%
- 80% (Correct answer)
- 70%
Correct answer: 80%
NEC Table 220.54 specifies an 80% demand factor when calculating the load for 4 clothes dryers.
Question 5: Under the NEC optional method for dwelling units (220.82), what percentage is applied to the load above the initial 10 kVA?
- 25%
- 40% (Correct answer)
- 50%
- 60%
Correct answer: 40%
NEC 220.82(B) applies 40% to all loads above the first 10 kVA when using the optional calculation method.
Question 6: A 1,200 sq ft dwelling has two small appliance circuits and one laundry circuit. What is the total load before demand factors for these circuits plus general lighting?
- 6,600 VA (Correct answer)
- 7,500 VA
- 8,100 VA
- 5,100 VA
Correct answer: 6,600 VA
Lighting: 1,200 × 3 = 3,600 VA; small appliances: 2 × 1,500 = 3,000 VA; total = 6,600 VA (laundry calculated separately under 220.52(B)).
Question 7: For a commercial building, NEC Table 220.12 assigns what unit lighting load (VA/sq ft) for office occupancies?
- 2.0 VA/sq ft
- 3.5 VA/sq ft
- 3.0 VA/sq ft (Correct answer)
- 1.5 VA/sq ft
Correct answer: 3.0 VA/sq ft
NEC Table 220.12 lists office occupancies at 3.5 VA/sq ft; however, many jurisdictions reference updated tables — the most common exam-tested value is 3.5 VA/sq ft.
IEC Service and Load Calculations 3
A 240-volt, 30-ampere clothes dryer circuit is installed in a dwelling.
What minimum load must be used for service calculation per NEC 220.54?