Master Electrician Exam (NEC)Load CalculationsEasy
A master electrician is performing a standard method load calculation for a single-family dwelling. The dwelling has a 4.5 kW electric water heater, a 3 kW dishwasher, and a 2 kW trash compactor. What is the demand load for these fixed appliances before applying any additional demand factors?
- A7.125 kW
- B9.5 kW
- C6.65 kW
- D8.55 kW
Show answer & explanationAnswer & explanation
Correct answer: A. 7.125 kW
According to NEC 220.53, for four or more fixed appliances, a demand factor of 75% can be applied to the sum of their nameplate ratings. The total connected load is 4.5 kW + 3 kW + 2 kW = 9.5 kW. Applying the 75% demand factor results in 9.5 kW * 0.75 = 7.125 kW.
Why the other options are wrong
- B. This is the sum of the nameplate ratings without applying the demand factor.
- C. This might result from an incorrect demand factor or calculation error.
- D. This might result from an incorrect demand factor or calculation error.
Fixed Appliance Demand Factor (Standard Method)
For four or more fixed appliances (other than electric ranges, clothes dryers, space heating, or A/C), a demand factor of 75% can be applied to the total nameplate rating.
- Applies to four or more fixed appliances.
- Excludes ranges, dryers, space heating, and A/C.
- Demand factor is 75% of the connected load.
Memory trick: Four or more fixed friends, 75% is the demand trend.