Single-phase or three-phase for a charging depot?

This surprises people who have read European material, where three-phase AC charging is normal and a three-phase 22 kW wallbox is an ordinary product. That equipment class does not exist in this market. Here, AC charging is single phase and the way you get more power is more amps, not more phases.It has a consequence that runs the wrong way from intuition. Move a Level 2 charger from a 240 volt single-phase service to a 120/208 volt three-phase service and each port gets slower, not faster, because 208 volts across two phases of a wye is less than 240 volts across a single-phase service. Same charger, same current setting, about thirteen percent less power.

Below that ceiling the question is arithmetic. A single-phase service gives you volts times amps; a three-phase service gives you volts times amps times 1.732. Take eighty percent for continuous load and divide by the power of one port.The table assumes nothing else is on the service, which is never true. Subtract your measured twelve-month peak first, factored the way the code requires, and the port counts drop.

This is the cleaner of the two triggers, because it is binary. No amount of single-phase service supports a DC cabinet. If your duty cycle has vehicles turning around mid-shift, or a rescue charger for the van that comes back empty at noon, you are buying three phase whether the Level 2 arithmetic needs it or not.The rest of the yard usually points the same way. Compressors, lifts, wash equipment and shop machinery are three-phase loads, so a depot with a maintenance building often already has a three-phase service and this whole question is moot. It is the bare yards — a fence, a gate, a lighting circuit and a small office — where single phase is genuinely on the table.

If the honest answer is that you might need it in three years, spend the money on the part that does not go obsolete. Oversize the conduit, pour the pads, set the pull boxes and leave the trench route clear. Passive infrastructure is cheap while the excavator is already on site and expensive once the yard is resurfaced.Buying the service early has a second cost that is easy to miss: the line-extension allowance is calculated on the load you actually connect. Connect a small load now and you get a small allowance now, and the allowance for the load you add later is a separate conversation with a separate estimate.

277/480 volt wye gives you 480 for DC cabinets and larger machinery and 277 for yard lighting, and it moves the same power through smaller conductors than 208 would, which matters when the run across a yard is long. What it does not give you is 208 or 240 for Level 2 chargers.So a large depot with Level 2 ports typically carries a dry-type step-down transformer feeding a 120/208 panel for the charging equipment. Budget the transformer, the pad or the room, the ventilation clearance and the secondary distribution. It is not a large fraction of the project, and it is a frequent omission from an early sketch.