Journeyman Electrician Exam (NEC)General Electrical Knowledge and Plan ReadingHard
A residential service calculation includes a 5.5 kW electric clothes dryer. According to NEC Article 220.54, what is the demand load for this dryer when performing a service calculation for a single-family dwelling?
- A4.0 kW
- B5.5 kW
- C6.0 kW
- D4.4 kW
Show answer & explanationAnswer & explanation
Correct answer: B. 5.5 kW
According to NEC Article 220.54, for clothes dryers, the demand load shall be 5000 watts (5 kW) or the nameplate rating, whichever is larger, for each dryer. In this case, the nameplate rating is 5.5 kW, which is larger than 5 kW, so the demand load is 5.5 kW.
Why the other options are wrong
- A. This is the minimum demand load (5 kW) if the nameplate rating was less than 5 kW, but 5.5 kW is larger.
- C. This is an arbitrary value not derived from the NEC rules for clothes dryers.
- D. This might be 80% of 5.5 kW, which is not the correct demand factor from NEC 220.54.
NEC Dryer Demand Load
NEC Article 220.54 specifies how to calculate the demand load for electric clothes dryers in service and feeder calculations.
- The demand load is 5000 W (5 kW) or the nameplate rating, whichever is larger, for each dryer.
- Demand factors apply if there are 4 or more dryers.
- This accounts for intermittent use and prevents oversizing.
Memory trick: Dryer: 5kW or Nameplate, pick the bigger one.