Free NEC Load Calculations Questions and Answers 1 — Questions and Answers
Question 1: An electrician is calculating the service load for a new 2,100 sq. ft. single-family dwelling. Using the standard method, what is the calculated load for the general lighting and general-use receptacles before any demand factors are applied?
- 4,500 VA
- 7,800 VA
- 6,300 VA (Correct answer)
- 3,000 VA
Correct answer: 6,300 VA
According to NEC 220.14(J), the minimum unit load for general lighting and general-use receptacles in a dwelling unit is 3 volt-amperes per square foot. The calculation is 2,100 sq. ft. x 3 VA/sq. ft. = 6,300 VA.
Question 2: When performing a standard load calculation for a dwelling unit, what is the MINIMUM total volt-ampere load that must be allocated for the small-appliance and laundry branch circuits?
- 3,000 VA
- 1,500 VA
- 6,000 VA
- 4,500 VA (Correct answer)
Correct answer: 4,500 VA
NEC 220.52(A) requires a load of 1,500 VA for each of the two (minimum) required small-appliance branch circuits (2 x 1,500 = 3,000 VA). NEC 220.52(B) requires 1,500 VA for the laundry circuit. The total minimum load is 3,000 VA + 1,500 VA = 4,500 VA.
Question 3: Using NEC Table 220.55, what is the calculated demand load for a single 13 kW household electric range for a service calculation?
- 13,000 VA
- 8,000 VA
- 8,400 VA (Correct answer)
- 12,000 VA
Correct answer: 8,400 VA
According to NEC Table 220.55, Column C, the demand for one range not over 12 kW is 8 kW (8,000 VA). Note 1 states that for ranges over 12 kW through 27 kW, the value in Column C shall be increased by 5% for each additional kW over 12 kW. This range is 1 kW over (13 kW - 12 kW = 1 kW). Therefore, the increase is 5%. The calculation is 8,000 VA * 1.05 = 8,400 VA.
Question 4: An electrician is calculating the feeder load for a multi-family dwelling with five identical apartments. Each apartment will have one electric clothes dryer with a nameplate rating of 4,800 watts. What is the total calculated demand load for the five dryers?
- 24,000 VA
- 21,250 VA
- 25,000 VA
- 20,000 VA (Correct answer)
Correct answer: 20,000 VA
Per NEC 220.54, the load for a household electric clothes dryer shall be 5,000 VA or the nameplate rating, whichever is larger. Since 4,800 W is less than 5,000 VA, each dryer is calculated at 5,000 VA. The total connected load is 5 dryers x 5,000 VA = 25,000 VA. According to Table 220.54, the demand factor for 5 dryers is 80%. Therefore, the calculated demand load is 25,000 VA x 0.80 = 20,000 VA.
Question 5: For a standard calculation, which of the following loads are combined together before applying the demand factors from NEC Table 220.42?
- General lighting, fixed appliances, and range load
- General lighting, small-appliance circuits, and laundry circuit (Correct answer)
- Small-appliance circuits, laundry circuit, and HVAC load
- General lighting, dryer load, and water heater load
Correct answer: General lighting, small-appliance circuits, and laundry circuit
In the standard method for dwelling unit load calculations, the general lighting load (3 VA/sq. ft.), the small-appliance circuit loads (1500 VA each), and the laundry circuit load (1500 VA) are added together. The demand factors from NEC Table 220.42 are then applied to this combined total.
Question 6: What is the minimum calculated general lighting load for a 12,000 sq. ft. office building before any demand factors are applied?
- 36,000 VA
- 168,000 VA (Correct answer)
- 120,000 VA
- 42,000 VA
Correct answer: 168,000 VA
According to NEC Table 220.12, the unit load for an office building is 14 VA per square foot. This value includes general-use receptacle loads. The calculation is 12,000 sq. ft. x 14 VA/sq. ft. = 168,000 VA.
Free NEC Load Calculations Questions and Answers 1
An electrician is calculating the service load for a new 2,100 sq. ft. single-family dwelling.
Using the standard method, what is the calculated load for the general lighting and general-use receptacles before any demand factors are applied?