Additional EVSEs are to be added to an existing 120/208-volt, 3-phase, 4-wire, 600-ampere service with 220 amperes of non-continuous load and 172 amperes of continuous load. The EVSEs each draw 32 amperes. How many new EVSEs can be added to the service?

Additional EVSEs are to be added to an existing 120/208-volt, 3-phase, 4-wire, 600-ampere service with 220 amperes of non-continuous load and 172 amperes of continuous load. The EVSEs each draw 32 amperes. How many new EVSEs can be added to the service?

• A. 2
• B. 3
• C. 6
• D. 9

Answer: (C)

At the heart of this is ensuring the service can handle the total current without exceeding its rating. The service is 600 A. The existing loads consume 220 A (non-continuous) plus 172 A (continuous), which sums to 392 A. Subtracting that from the service rating leaves 600 − 392 = 208 A available for new equipment. Each new EVSE draws 32 A, so the maximum number of EVSEs you could add is 208 ÷ 32 = 6.5. Since you can’t have a fraction of an EVSE, you can add six. Note: in real NEC-like calculations you’d consider demand factors for continuous vs non-continuous loads, but this problem uses a straightforward remaining-ampacity approach, yielding six additional EVSEs.

At the heart of this is ensuring the service can handle the total current without exceeding its rating. The service is 600 A. The existing loads consume 220 A (non-continuous) plus 172 A (continuous), which sums to 392 A.

Subtracting that from the service rating leaves 600 − 392 = 208 A available for new equipment.

Each new EVSE draws 32 A, so the maximum number of EVSEs you could add is 208 ÷ 32 = 6.5. Since you can’t have a fraction of an EVSE, you can add six.

Note: in real NEC-like calculations you’d consider demand factors for continuous vs non-continuous loads, but this problem uses a straightforward remaining-ampacity approach, yielding six additional EVSEs.