Each apartment in a 50-unit apartment complex has a 4 kW electric clothes dryer. The service for the apartment complex is 120/208V 3-phase 4-wire. Using the standard method, what is the demand on the service for these dryers?

Each apartment in a 50-unit apartment complex has a 4 kW electric clothes dryer. The service for the apartment complex is 120/208V 3-phase 4-wire. Using the standard method, what is the demand on the service for these dryers?

• A. 59.5 kW
• B. 68.85 kW
• C. 136 kW
• D. 170 kW

Answer: (B)

The key idea is using the standard method to apply a demand factor to multiple appliances rather than just summing their nameplate loads. For clothes dryers in a dwelling, you take the total connected load and multiply it by a demand factor that depends on how many units are in service. First, find the total connected load: 50 units × 4 kW each = 200 kW. Then apply the standard-method demand factor for the number of units. For 50 units, the factor is about 0.34425. Multiplying gives 200 kW × 0.34425 ≈ 68.85 kW. So the demand on the service for these dryers is 68.85 kW. (The 120/208V, 3-phase 4-wire service affects the current this load would draw, but the calculation here yields the kW demand.)

The key idea is using the standard method to apply a demand factor to multiple appliances rather than just summing their nameplate loads. For clothes dryers in a dwelling, you take the total connected load and multiply it by a demand factor that depends on how many units are in service.

First, find the total connected load: 50 units × 4 kW each = 200 kW.

Then apply the standard-method demand factor for the number of units. For 50 units, the factor is about 0.34425. Multiplying gives 200 kW × 0.34425 ≈ 68.85 kW.

So the demand on the service for these dryers is 68.85 kW. (The 120/208V, 3-phase 4-wire service affects the current this load would draw, but the calculation here yields the kW demand.)