Master Electrician Exam (NEC)Load CalculationsMedium
A master electrician is performing a standard method load calculation for a single-family dwelling. The dwelling has a 12 kW electric range, a 5.5 kW electric dryer, and a 4 kW electric water heater. What is the calculated demand load for these fixed appliances before applying general lighting and receptacle loads?
- A21.5 kW
- B19.5 kW
- C18.25 kW
- D16.125 kW
Show answer & explanationAnswer & explanation
Correct answer: D. 16.125 kW
According to NEC 220.53, for four or more fixed appliances, other than electric ranges, clothes dryers, space heating equipment, or air-conditioning equipment, a demand factor of 75% can be applied to the nameplate rating of the appliances. The range and dryer are calculated separately, leaving only the water heater for the fixed appliance demand.
Why the other options are wrong
- A. This incorrect option likely sums all loads without applying any demand factors, which is not permitted by the NEC.
- B. This incorrect option does not apply the correct demand factor or misinterprets which appliances are subject to it.
- C. This incorrect option likely applies the demand factor to more appliances than allowed or miscalculates the demand factor.
Fixed Appliance Demand (Standard Method)
For four or more fixed appliances (excluding ranges, dryers, space heating, and A/C), a 75% demand factor is applied to their total nameplate rating in a standard load calculation.
- Applies to 'fixed appliances' as defined by NEC 220.53.
- Excludes ranges, dryers, space heating, and air conditioning.
- Requires four or more such appliances to apply the 75% demand factor.
Memory trick: Four fixed friends get a 75% discount.