EV Chargers and NEC 220.84

[liverpool]

Can the demand factor shown on table 220.8 be used for Electrical Vehicle Chargers if they are being fed from the dwelling panels?

 

[NoahsArc]

84?
EVs (in 2020 at least) aren't very explicitly mentioned much, are somewhat unusual and high loads, and I'd just ask the AHJ.

 

[jaggedben]

Strictly speaking it's allowed, but I agree with Noah because I've had AHJs make their own rules about EV charging. Also in some circumstances it may just be a bad idea.

 

[wwhitney]

Can the demand factor shown on table 220.8 be used for Electrical Vehicle Chargers if they are being fed from the dwelling panels?

Certainly that is the meaning of the text in 220.84.

Some caution is advised, as the NEC is apparently behind in adjusting Article 220 for EVSE loads. It's not too hard to come up with hypotheticals where the 220.84 calculation would be non-conservative if every dwelling unit supplies an EVSE, and if there's any chance of a significant fraction of those being used simultaneously. So you might wish to seek another source for suitable demand factors for EVSEs based on the number of EVSEs installed, and then for the EVSEs voluntarily use the larger of that demand factor and the 220.84 demand factor.

For reference, up through the 2023 NEC the same issue applies with EVSEs at a single dwelling unit under 220.82. The 2026 NEC First Draft includes a new section 120.82(D) (article 220 got renumbered to 120) which says "The total load of an EVSE shall be calculated at 100 percent in accordance with 120.57." But 220.84 did not get any such amendment.

Cheers, Wayne

 

[Elect117]

There are a bunch of posts on this subject. You can probably find most of the back and forth between Wanye and I.

To summarize:
I think that the way 220.80 / 220.40 are written excludes special equipment as being included in the demand factors.

The only way to assume that it can be is to think that it is an appliance, to which it is not. The code specifies it as EVSE.

 

[jaggedben]

...
To summarize:
I think that the way 220.80 / 220.40 are written excludes special equipment as being included in the demand factors.
...

Gonna have to take Wayne's side and disagree with you, even though I think it imprudent to push the boundaries too much while waiting for the code to catch up to EV charging.

 

[pv_n00b]

This is covered in 625.42. If an EMS limits the maximum demand of a group of chargers then the feeder and branch circuits can be designed to the EMS limited demand. The chargers can also be derated if they are adjustable and the adjustment can be locked, but that makes for a poor user experience when trying to charge their car.
I would think that even when aggregated across dwelling panels the feeders need to be rated based on 625.42 for all attached chargers.

 

[tortuga]

Since 220.84 typically only applies to the service lateral feeding the meter pack and the size of the meter pack service busbar I am gonna say its unlikely a problem including the EVSE's in 220.84, especially when you look at the size of the transformer the lateral connects to. If you post your calc and the utility transformer size we can take a look.

 

[ggunn]

Would there be anything wrong with considering the EV chargers in a bank of them to be continuous loads and sizing the wiring and OCP to the worst case condition, which would be all of them running as such at full capacity at the same time?

 

[jaggedben]

Would there be anything wrong with considering the EV chargers in a bank of them to be continuous loads and sizing the wiring and OCP to the worst case condition, which would be all of them running as such at full capacity at the same time?

?
You mean if that were a larger service size than the 220.84 required calc?

Note the OP said the EVSEs would be fed from the dwelling panels so I don't know why we'd be talking about a 'bank' or group of EVSEs.

 

[ggunn]

?
You mean if that were a larger service size than the 220.84 required calc?

Note the OP said the EVSEs would be fed from the dwelling panels so I don't know why we'd be talking about a 'bank' or group of EVSEs.

Yes, I mean if the service is much larger than than all the loads combined. Sorry that I diverted the question.

 

[Elect117]

Would there be anything wrong with considering the EV chargers in a bank of them to be continuous loads and sizing the wiring and OCP to the worst case condition, which would be all of them running as such at full capacity at the same time?

If I understanding your question, then no. There is nothing wrong with oversizing the circuits that feed the EV charger(s). Nor is there anything wrong with overestimating their effects.

The only time that might be a pain is if they plan of back feeding but I really prefer not to get into all that nuance. Because then we are talking about 705 and load side connections and so on.

 

[tortuga]

When your all driving around take a look at what size transformers utilities install, its amusing, I was at a place that had a 17 unit complex, 17 100A services grouped in meter packs, plus a 200A house panel that served a laundry room, I think the utility transformer was a 50kVA.

 

[ggunn]

If I understanding your question, then no. There is nothing wrong with oversizing the circuits that feed the EV charger(s). Nor is there anything wrong with overestimating their effects.

Thanks. I had to design a couple of banks like this, and it being somewhat out of my wheelhouse I wanted to be conservative.

 

[kingpb]

When your all driving around take a look at what size transformers utilities install, its amusing, I was at a place that had a 17 unit complex, 17 100A services grouped in meter packs, plus a 200A house panel that served a laundry room, I think the utility transformer was a 50kVA.

Utilities have a lot of data on demand versus connected. Plus, they have no problem overloading their transformers because data shows it is cheaper for them to shorten the life of the transformer for limited over load conditions versus the cost of installing one that is lightly loaded most of the time.