FREE NEC Load Calculations 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?

Accepted Answer

6,300 VA

Answer

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?

Accepted Answer

4,500 VA

Answer

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?

Accepted Answer

8,400 VA

Answer

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?

Accepted Answer

20,000 VA

Answer

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?

Accepted Answer

General lighting, small-appliance circuits, and laundry circuit

Answer

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.

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FREE NEC Load Calculations Questions and Answers