Size the electrical supply for EV chargers in car parks, buildings and charging hubs. Add AC and DC chargers, and the calculator balances them across the phases, then sizes the main breaker, each branch breaker and the transformer to NEC 625 or IEC 60364-7-722, with or without a load management system.
Preliminary sizing. Cable sizes, voltage drop, short-circuit ratings and selectivity must be checked separately, and the charger manufacturer's installation data and local utility rules apply.
An EV charger draws close to its full rated current for hours at a time, so electrical codes treat it as a continuous load and do not let you assume that only some chargers run at once, unless a load management system enforces it. The calculation is therefore simple but strict:
The NEC has no demand factor for EV chargers. Without load management, every charger counts at full rating.
Ten 7.4 kW single-phase AC chargers (32 A) and two 50 kW DC chargers on a 400 V three-phase supply, no load management:
With a load management system limited to 150 kW, the design current drops to 221 A and a 250 A breaker is enough. Under the NEC the same loads need breakers rated 125% of these currents.
Size each charger cable with the Cable Size Calculator and check the feeder with the Voltage Drop Calculator. For the transformer itself see the Transformer Sizing Calculator.
Add the rated current of every charger on each phase (AC chargers at their rated amps, DC chargers at output power ÷ efficiency ÷ voltage), take the highest phase current, and size the breaker at 125% of it under the NEC or at least equal to it under IEC. Only a load management system lets you use a lower figure.
A 7.4 kW charger draws 32 A on 230 V. Under IEC a 32 A or 40 A breaker with a Type A RCD and 6 mA DC detection is typical. A 7.7 kW charger at 240 V under the NEC draws 32 A and needs a 40 A breaker (125%).
Not without load control. IEC 60364-7-722 takes the diversity factor as 1 unless load control is installed, and the NEC has no demand factor for EVSE; NEC 625.42 lets you use the limit of an automatic load management system instead.
Under IEC 60364-7-722 each charging point needs its own RCD of at least Type A, 30 mA, plus protection against DC fault current: a Type B RCD, or Type A with a 6 mA DC detection device, unless the charger has it built in.
Because the breaker and transformer are sized on the most loaded phase. Ten single-phase chargers all on one phase would need three times the capacity of the same chargers spread evenly over three phases.
Found a number that looks wrong, or a case the tool does not cover? Say so here — corrections are welcome and get answered.
No comments yet. Be the first to add one.