Master Electrician Exam (NEC)Load CalculationsMedium
A master electrician is performing an optional method load calculation for a single-family dwelling (NEC 220.82). The dwelling has a total general lighting and receptacle load of 10,000 VA, an electric range of 12 kW, a 5 kW electric water heater, and a 2 kW dishwasher. There is also a 10 kW central electric space heating system. What is the demand load for the electric space heating system using this method?
- A10 kW
- B5 kW
- C6.5 kW
- D7.5 kW
Show answer & explanationAnswer & explanation
Correct answer: A. 10 kW
According to NEC 220.82(C)(5), the largest of the heating or air-conditioning loads is taken at 100% when using the optional method for dwelling units. Since there is only a heating load mentioned, it is taken at its full value.
Why the other options are wrong
- B. This is incorrect; it applies an incorrect demand factor to the heating load.
- C. This is incorrect; it applies an incorrect demand factor to the heating load.
- D. This is incorrect; it applies an incorrect demand factor to the heating load.
Optional Method Heating/A/C Load
When using the optional method (NEC 220.82) for dwelling units, the largest of the electric space heating or air-conditioning loads is included at 100% of its nameplate rating.
- Applies to dwelling units using the optional calculation method.
- Only the larger of heating or A/C is considered.
- The selected load is included at 100% of its rating.
- This differs from standard method where other demand factors might apply to heating.
Memory trick: Optional heating: No discount, 100% is the count!