Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingHard
A new service for a multi-family dwelling requires a demand load calculation. The dwelling unit has a 12 kW electric range, a 4 kW electric dryer, and a 10 kW central electric heating system. According to NEC Article 220, what is the demand load for the electric range, after applying the appropriate demand factor?
- A8 kW
- B10 kW
- C12 kW
- D9.6 kW
Show answer & explanationAnswer & explanation
Correct answer: A. 8 kW
According to NEC Table 220.55, for household electric ranges over 8.75 kW, Column C is used. For one range, the demand load is 8 kW. The 12 kW rating is the nameplate rating, but the demand factor reduces this for service calculations.
Why the other options are wrong
- B. This might come from an incorrect application of a demand factor or misreading the table.
- C. This is the nameplate rating, not the demand load after applying NEC factors.
- D. This might be 80% of 12 kW, which is not the correct demand factor from NEC 220.55.
NEC Range Demand Factors
NEC Table 220.55 provides demand factors for household electric ranges, cooktops, and ovens to account for their intermittent use in service and feeder calculations.
- For one range over 8.75 kW, the demand load is 8 kW (Column C).
- For ranges 3.5 kW to 8.75 kW, Column A, B, or C may apply depending on quantity.
- These factors prevent oversizing service conductors and overcurrent protection.
Memory trick: Ranges: 220.55, 8kW is the magic number for one big one.