How many new EVSEs can be added to a 600 A service with 220 A non-continuous and 172 A continuous, given each EVSE draws 32 A, using three-phase calculations?

How many new EVSEs can be added to a 600 A service with 220 A non-continuous and 172 A continuous, given each EVSE draws 32 A, using three-phase calculations?

• A. 2
• B. 3
• C. 6
• D. 9

Answer: (C)

The key idea is to check the service’s capacity by accounting for existing loads and then see how many new EVSEs can fit without exceeding that capacity. Add up the existing currents: 220 A (non-continuous) plus 172 A (continuous) equals 392 A. Subtract this from the 600 A service rating to find the remaining capacity: 600 − 392 = 208 A available for new loads. Each EVSE draws 32 A, so the number of additional EVSEs you can support is 208 ÷ 32 = 6.5. Since you can’t install half a charger, the maximum is six EVSEs. If you tried seven, you’d need 224 A more than you have available, which would exceed the service. Note: in a more formal NEC-based calculation you’d derate continuous loads (125%), convert to VA, and compare to the service’s VA rating, which could yield a different result. This question uses a straightforward current-based check, giving six.

The key idea is to check the service’s capacity by accounting for existing loads and then see how many new EVSEs can fit without exceeding that capacity. Add up the existing currents: 220 A (non-continuous) plus 172 A (continuous) equals 392 A. Subtract this from the 600 A service rating to find the remaining capacity: 600 − 392 = 208 A available for new loads. Each EVSE draws 32 A, so the number of additional EVSEs you can support is 208 ÷ 32 = 6.5. Since you can’t install half a charger, the maximum is six EVSEs. If you tried seven, you’d need 224 A more than you have available, which would exceed the service.

Note: in a more formal NEC-based calculation you’d derate continuous loads (125%), convert to VA, and compare to the service’s VA rating, which could yield a different result. This question uses a straightforward current-based check, giving six.