Master Electrician Exam (NEC)Load CalculationsMedium
A commercial building has a total connected load of 150 kVA, consisting of general lighting, receptacles, and fixed equipment. The building operates for 10 hours a day, 5 days a week. The calculated maximum demand over a 15-minute interval is 105 kVA. What is the demand factor for this building's service calculation?
- A0.70
- B0.60
- C0.75
- D0.80
Show answer & explanationAnswer & explanation
Correct answer: A. 0.70
The demand factor is the ratio of the maximum demand of a system, or part of a system, to the total connected load of the system, or part of the system under consideration. In this case, the demand factor is 105 kVA (maximum demand) / 150 kVA (total connected load) = 0.70.
Why the other options are wrong
- B. Incorrect calculation. This would imply a maximum demand of 90 kVA.
- C. Incorrect calculation. This would imply a maximum demand of 112.5 kVA.
- D. Incorrect calculation. This would imply a maximum demand of 120 kVA.
Demand Factor
The ratio of the maximum demand of a system, or part of a system, to the total connected load of the system or part of the system under consideration.
- Demand Factor = Maximum Demand / Total Connected Load.
- Always less than or equal to 1.
- Used to size feeders and services more accurately.
Memory trick: Demand is always 'down' from the total connected load.