Understanding how to size panel for ev chargers

brianthejabroni2

Member
Can somebody point me in the right direction or maybe show me a video or even just explain what are the proper steps for sizing a three phase panel. I am trying to determine how many 32 AMP EV chargers I can put on a panel.

tom baker

First Chief Moderator
Staff member
What is the secondary voltage for the panel, and what is the EV charger name plate rating?

brianthejabroni2

Member
208v secondary and 32amp nameplate on charger

wwhitney

Senior Member
If you put (3) of those units in a balanced configuration on a 208Y/120V system, then at full load each line current will be 32A * sqrt(3) = 55.4A. EVSEs require a 125% continuous use factor, so that makes it 69.3A per balanced triple.

Thus a 70A panel could support 3; a 150A panel could support 6; and a 225A panel could support 9, if they are the only loads. Etc.

If you have, say a 400A panel, then you could support 5 triples at 346.5A. The remaining capacity of 53.5A is greater than 40A (32A * 125%), so you could put one more on the panel on any phase. [And actually, you wouldn't quite need 40A of remaining capacity to add an extra, due to the vector addition.]

Cheers, Wayne

rojay

Senior Member
I think 220.57 of the 2023 NEC might change some of the figures. I’m kind of confused on whether or not the 125% factor is applied to service conductors?

wwhitney

Senior Member
I think 220.57 of the 2023 NEC might change some of the figures.
Ugh, that's a stupid section--it imposes a minimum load to use of 7200 VA, which the accompanying panel statement says is based on 30A @ 240V. But many EVSEs are on 208Y/120V systems, like in the OP. So the use of a minimum based on 240V make no sense to me.

If the OP is under the 2023 NEC, and the EVSE load is considered continuous (see 625.41, it doesn't quite come out and say it has to be considered continuous), then the upshot is that a triple of EVSEs requires 80A of feeder/OCPD capacity, rather than 69.3A.

I’m kind of confused on whether or not the 125% factor is applied to service conductors?
The 125% factor from 625.41 does not, as that specifies that it applies to feeders and branch circuits. If the EVSE load is continuous, then it would apply as a continuous use factor to service entrance conductors, but not necessarily other service conductors. If there is just one service OCPD, then it would apply to the service OCPD and thus to the service conductors. But with multiple service OCPD, it is possible to have service conductors not subject to the 125% continuous use factor.

Cheers, Wayne

Kidd

Member
@wwhitney
Out of curiosity, if the name plate on the EV charger said 32A @ 240V, are all EVSE's chargers considered a resistive load? So the amperage would go down to 27.7 amps right?

retirede

Senior Member
@wwhitney
Out of curiosity, if the name plate on the EV charger said 32A @ 240V, are all EVSE's chargers considered a resistive load? So the amperage would go down to 27.7 amps right?

No, a 32A EVSE will allow the car to charge at up to 32A regardless of the voltage.