Multi-Family Building with EV Chargers

[JoeStillman]

When we did our dwelling unit feeder calculations, we included EV Chargers among the "...appliances that are fastened in place, permanently connected, or located to be on a specific circuit" [220.82(B)(3).a.], which makes it part of the 1st 10 kVA plus 40% of the rest. The overall service calculation includes them under the diversities of Table 220.84.

A plan reviewer is telling us we may not apply either of these diversity factors to the EV Chargers. Am I missing something in The Code?

 

[wwhitney]

Has the jurisdiction adopted any relevant amendments? Have they given an interpretation of the code sections as to why they don't apply?

I agree with you that 220.82 as currently written does not distinguish between EVSEs and other equipment (like it does for HVAC equipment in 220.82(C)), and as such they end up with a 40% factor. And likewise the demand factors in Table 220.84 would apply for multifamily buildings.

However, there is a real problem with that approach. Say you have a 15 unit building and you add a 40A (continuous) EVSE to each unit. The two factors you identified mean that the optional load calculation only goes up 40% * 40% * 15 * 40A = 96A. But it only takes 3 of those 15 EVSEs drawing full current to actually exceed that. And as EV adoption grows, that level of utilization and more will regularly occur.

So there's definitely room for improvement in Article 220 Part IV with respect to EVSEs. Of course a formal amendment to the language is the best approach, rather than some likely tortuous reinterpretation of the existing language.

Cheers, Wayne

 

[JoeStillman]

Has the jurisdiction adopted any relevant amendments? Have they given an interpretation of the code sections as to why they don't apply?

I agree with you that 220.82 as currently written does not distinguish between EVSEs and other equipment (like it does for HVAC equipment in 220.82(C)), and as such they end up with a 40% factor. And likewise the demand factors in Table 220.84 would apply for multifamily buildings.

However, there is a real problem with that approach. Say you have a 15 unit building and you add a 40A (continuous) EVSE to each unit. The two factors you identified mean that the optional load calculation only goes up 40% * 40% * 15 * 40A = 96A. But it only takes 3 of those 15 EVSEs drawing full current to actually exceed that. And as EV adoption grows, that level of utilization and more will regularly occur.

So there's definitely room for improvement in Article 220 Part IV with respect to EVSEs. Of course a formal amendment to the language is the best approach, rather than some likely tortuous reinterpretation of the existing language.

Cheers, Wayne

That 40% also applies to all the ranges, dryers and water heaters. I wonder if EV chargers are more likely to be online simultaneously than that stuff. The reviewer seems to think so.

 

[wwhitney]

I wonder if EV chargers are more likely to be online simultaneously than that stuff.

Since they are continuous loads, I would certainly expect so. As an EV owner, it's fairly common to charge for over 3 hours at maximum current. Whereas, how long does a washer draw its maximum current?

Cheers, Wayne

 

[Dennis Alwon]

This issue came up in the area I live in and I was convinced that the best way, not code necessarily, was to install those units at 100% with no demand.

 

[synchro]

Will the EV chargers have any load management system that can limit the maximum current draw?

 

[don_resqcapt19]

I don't see an EV charger as an appliance, so I would not include them in the section that was cited, if I was reviewing your load calculations.

 

[wwhitney]

I don't see an EV charger as an appliance, so I would not include them in the section that was cited, if I was reviewing your load calculations.

220.82 has only two sections, (B) "General Loads" and (C) "Heating and Air-Conditioning Load". The EVSE/EV charger/EV is certainly not the latter, so it must fall under (B).

Cheers, Wayne

 

[don_resqcapt19]

220.82 has only two sections, (B) "General Loads" and (C) "Heating and Air-Conditioning Load". The EVSE/EV charger/EV is certainly not the latter, so it must fall under (B).

Cheers, Wayne

I guess it has to be as those are the total load for the dwelling

 

[don_resqcapt19]

So looking at it again, I think you use 220.82 for the individual feeders, but apply the factors in Table 220.84 to the result of 220.84(C).

 

[JoeStillman]

So looking at it again, I think you use 220.82 for the individual feeders, but apply the factors in Table 220.84 to the result of 220.84(C).

Exactly. The single-family calc has no impact on the multi-family one. I confirmed with NFPA that all the loads required in both of these calculations are considered non-continuous.

I always thought that battery charge current tapers off as charge accumulates - they don't draw full current the whole time. Are EV chargers different?

 

[wwhitney]

I always thought that battery charge current tapers off as charge accumulates - they don't draw full current the whole time. Are EV chargers different?

The batteries in EVs are often large enough relative to the on-board charger size that they can remain in the constant current state for over 3 hours, depending on the starting state of charge of the battery. E.g. a nominal 60 kWh battery with a nominal 7.2 kW on-board charger.

Cheers, Wayne

 

[Barbqranch]

I am surprised the EV companies don't use full current for 2 hours and then drop down to 80% for the next hour.

 

[wwhitney]

I am surprised the EV companies don't use full current for 2 hours and then drop down to 80% for the next hour.

There would be no point in that, as 625.41 requires sizing EVSE circuits for continuous use.

Cheers, Wayne

 

[retirede]

I am surprised the EV companies don't use full current for 2 hours and then drop down to 80% for the next hour.

Most tech-savvy EV owners would recognize this and not buy equipment that wasn’t capable of maximum charge rate up until the car reached the desired charge level.

 

[HuntNJ]

Will the EV chargers have any load management system that can limit the maximum current draw?

Yes. Most chargers I’ve installed have load sharing. So you can put up to four chargers on one 60 amp circuit and you can manage which charger has priority or if you want them to split the load equally.

 

[robertd]

Yes. Most chargers I’ve installed have load sharing. So you can put up to four chargers on one 60 amp circuit and you can manage which charger has priority or if you want them to split the load equally.

That may be fine for a single family home but I don't see that working in a multifamily dwelling. If I have only one car and I'm paying full price for the electricity I expect full power to charge my car. If someone wants to throttle my power usage that's gone to cost them.

 

[retirede]

That may be fine for a single family home but I don't see that working in a multifamily dwelling. If I have only one car and I'm paying full price for the electricity I expect full power to charge my car. If someone wants to throttle my power usage that's gone to cost them.

If you give residents of a multi-tenant dwelling the choice of charging with a shared capacity vs no charging at all, they’ll take the shared arrangement every time. This will be the most common arrangement going forward, imo.
It’s not going to be practical to install a bank of EVSEs capable of simultaneous full output that are going to be utilized a low percentage of the time.