IEC - Independent Electrical Contractors Service and Load Calculations Questions and Answers

Question 1

When calculating the service load for a 2,500 sq. ft. single-family dwelling using the standard method, what is the total VA that must be allocated for the required small-appliance and laundry branch circuits before any demand factors are applied?

Accepted Answer

4,500 VA

Answer

According to NEC 220.52, a dwelling unit requires at least two 20-ampere small-appliance branch circuits and one 20-ampere laundry branch circuit. Each of these required circuits is calculated at 1,500 VA. Therefore, the total is (2 x 1,500 VA) + (1 x 1,500 VA) = 4,500 VA.

Question 2

An electrician is calculating the service for a single-family dwelling using the optional method per NEC Article 220, Part IV. The total calculated general load is 32,000 VA. How is the demand factor applied to this load?

Accepted Answer

The first 10,000 VA at 100%, and the remainder at 40%

Answer

NEC 220.82(B) specifies the demand factor for the optional method calculation for a dwelling unit. The first 10,000 VA of the general load is calculated at 100%, and the remainder of the load is calculated at 40%. So, (10,000 VA * 1.0) + ((32,000 VA - 10,000 VA) * 0.40) = 10,000 VA + 8,800 VA = 18,800 VA.

Question 3

Which of the following loads in a dwelling unit is subject to a 75% demand factor when four or more are fastened in place and served by the same feeder or service?

Accepted Answer

Fixed appliances like a water heater, dishwasher, garbage disposal, and trash compactor

Answer

NEC 220.53 permits a 75% demand factor to be applied to the nameplate ratings of four or more fastened-in-place appliances served by the same feeder or service. This rule specifically excludes electric ranges, clothes dryers, space-heating equipment, and air-conditioning equipment, which have their own specific calculation rules.

Question 4

You are calculating the receptacle load for a 15,000 sq. ft. office building. The plans show 120 individual 125V receptacles. According to NEC 220.14(I) and Table 220.44, what is the calculated load after applying the appropriate demand factor?

Accepted Answer

15,800 VA

Answer

First, calculate the total connected receptacle load: 120 receptacles × 180 VA per receptacle = 21,600 VA. Then, apply the demand factor from NEC Table 220.44, which allows the first 10 kVA (10,000 VA) at 100% and the remainder at 50%. Calculation: 10,000 VA + ((21,600 VA - 10,000 VA) × 0.50) = 10,000 VA + 5,800 VA = 15,800 VA.

Question 5

For a commercial kitchen with six pieces of equipment, NEC 220.56 states that the feeder or service calculated load shall not be less than the sum of the ________.

Accepted Answer

largest two kitchen equipment loads

Answer

NEC 220.56 contains a provision that, regardless of the demand factors applied from Table 220.56, the final calculated load for commercial kitchen equipment cannot be less than the sum of the largest two kitchen equipment loads. This ensures the service is adequately sized for a worst-case scenario where the two biggest pieces of equipment run simultaneously.

IEC - Independent Electrical Contractors Practice Test

IEC - Independent Electrical Contractors Practice Test

IEC - Independent Electrical Contractors Service and Load Calculations Questions and Answers