What is the minimum copper THHN feeder size for 12 EVSEs rated at 24 amperes each on a 3-phase, 4-wire, 120/208-volt system?

To determine the minimum copper THHN feeder size for a setup with 12 Electric Vehicle Supply Equipment (EVSE) units each rated at 24 amperes on a 3-phase, 4-wire, 120/208-volt system, it's essential to calculate the total load and apply the appropriate ampacity standards.

First, calculate the total load from the 12 EVSEs:

Total load = Number of EVSEs × Load per EVSE

Total load = 12 × 24 A = 288 A.

Since this is a 3-phase system, the actual current that will be drawn by the feeder must consider the three phases, leading to a total load on the three-phase system. In practice, for three-phase loads, you can use the formula to determine the current:

I = Total Load / √3.

However, most practical situations apply a safety factor which typically is factored into adjustments for diversity and demand.

When selecting the conductor size based on the National Electrical Code (NEC) or similar code enforcement standards, you need to take into consideration the ampacity of the conductor, ambient temperature, and how many conductors are in the same conduit, among other factors.

With a continuous load (which