Multiple EV chargers (NON LOAD SHARING)

[shawjw]

Scope: install 3 chargepoint home Flex evse. Max charging output is 48 amps each. Single phase , level two. Non-managed

Cont. Load 125% = 60 amps O.C.P.D. #6 thhn
? Can the feeder be sized like a motor circuit.

60 amps + 48 amps + 48 amps = 156 amps (2/0 thhn)
Thx

 

[wwhitney]

625.41 says no, the feeder needs to be sized at 180A (for a 2-wire 240V or 208V feeder).

Cheers, Wayne

 

[Fred B]

Can the multiple loads be made compliant if a device is installed that would restrict or prevent the the loads being on at same time? Like using a breaker lockout used for a generator back feed.

 

[Seekthetruth]

625.41 says no, the feeder needs to be sized at 180A (for a 2-wire 240V or 208V feeder).

Cheers, Wayne

For household load calculations (optional method) does a EV charger have to be computed at 125% instead of 40% in reference to 625.41 (42)?

 

[wwhitney]

I find it a bit odd that article 220 doesn't mention continuous vs non-continuous loads. So my assumption has always been that when doing an article 220 calculation, each input load comes with a little label on it that say "continuous" or "non-continuous" and you track that label through all the calculations. E.g. at an any point in the calculation instead of having an intermediate answer of say, 100A, the intermediate answer is, say, 60A non-continuous plus 40A continuous.

So then 625 tells us an EVSE is a continuous load, but the 220 optional method allows a 40% factor for "general loads." [Although it doesn't specify which portion of the first 10 kVA of general loads should get the 100% factor, one could argue that to be conservative, that the 100% factor should apply to any continuous loads before any non-continuous loads.]

This of course leads to potentially contradictory results such as this: say the optional calculation gives you 80A for (2) 40A continuous EVSEs, 50A of additional general loads (non-continuous), and gas heat. [For simplicity I'm going to inaccurately treat 10kVA as 9600 kVA (40A @ 240V)]. The total optional method load is 40A + 0.4 *(90A) = 76A. Which is less than the 80A of the EVSEs.

Cheers, Wayne

 

[MyCleveland]

I find it a bit odd that article 220 doesn't mention continuous vs non-continuous loads. So my assumption has always been that when doing an article 220 calculation, each input load comes with a little label on it that say "continuous" or "non-continuous" and you track that label through all the calculations. E.g. at an any point in the calculation instead of having an intermediate answer of say, 100A, the intermediate answer is, say, 60A non-continuous plus 40A continuous.

So then 625 tells us an EVSE is a continuous load, but the 220 optional method allows a 40% factor for "general loads." [Although it doesn't specify which portion of the first 10 kVA of general loads should get the 100% factor, one could argue that to be conservative, that the 100% factor should apply to any continuous loads before any non-continuous loads.]

This of course leads to potentially contradictory results such as this: say the optional calculation gives you 80A for (2) 40A continuous EVSEs, 50A of additional general loads (non-continuous), and gas heat. [For simplicity I'm going to inaccurately treat 10kVA as 9600 kVA (40A @ 240V)]. The total optional method load is 40A + 0.4 *(90A) = 76A. Which is less than the 80A of the EVSEs.

Cheers, Wayne

Excellent analysis Wayne…exactly why from a prior debate I cannot get on board in using the 40% discount on chargers.

 

[wwhitney]

Excellent analysis Wayne…exactly why from a prior debate I cannot get on board in using the 40% discount on chargers.

There's a difference between "it's allowed but it's not best practice so I'm unlikely to do it" and "the AHJ should disallow it, despite no language in the NEC to support that position." I can agree with the former but not the latter.

The "contradictory result" case I described is pretty unlikely. If it actually caused a dwelling unit main feeder breaker to trip, the user can decide to upgrade the feeder or dial down the EVSEs.

Cheers, Wayne

 

[jaggedben]

Can the multiple loads be made compliant if a device is installed that would restrict or prevent the the loads being on at same time? Like using a breaker lockout used for a generator back feed.

Yes, but I take the 'Non Load Sharing' portion of the thread subject line to mean that is not being done here.

 

[Seekthetruth]

I find it a bit odd that article 220 doesn't mention continuous vs non-continuous loads. So my assumption has always been that when doing an article 220 calculation, each input load comes with a little label on it that say "continuous" or "non-continuous" and you track that label through all the calculations. E.g. at an any point in the calculation instead of having an intermediate answer of say, 100A, the intermediate answer is, say, 60A non-continuous plus 40A continuous.

So then 625 tells us an EVSE is a continuous load, but the 220 optional method allows a 40% factor for "general loads." [Although it doesn't specify which portion of the first 10 kVA of general loads should get the 100% factor, one could argue that to be conservative, that the 100% factor should apply to any continuous loads before any non-continuous loads.]

This of course leads to potentially contradictory results such as this: say the optional calculation gives you 80A for (2) 40A continuous EVSEs, 50A of additional general loads (non-continuous), and gas heat. [For simplicity I'm going to inaccurately treat 10kVA as 9600 kVA (40A @ 240V)]. The total optional method load is 40A + 0.4 *(90A) = 76A. Which is less than the 80A of the EVSEs.

Cheers, Wayne

Good point. Being that many more homes will be getting these chargers shouldn't they address this issue like they do the heating and air-conditioning in the optional method?

 

[wwhitney]

Good point. Being that many more homes will be getting these chargers shouldn't they address this issue like they do the heating and air-conditioning in the optional method?

Sure, but that hasn't happened yet. I checked the 2023 First Draft Report. There was a proposal to add demand factors for large numbers of EVSEs in the Standard Method. It became simply a requirement for a minimum of 7200 VA per EVSE, a new section 220.57. There's no change to the Optional Method, so I assume that will await a PI for the 2026 NEC.

Cheers, Wayne

 

[petersonra]

why would you allow for a lesser service when you are adding loads that are likely to be on simultaneously?

 

[Seekthetruth]

why would you allow for a lesser service when you are adding loads that are likely to be on simultaneously?

Does this mean it is up to the AHJ whether to allow the 40%?