Electric Vehicle Charging

LibertyEngineering

Senior Member
Location
Allentown, PA
I see that branch circuits are required to be designed to 125% for EV chargers because they are considered continuous load. I assume a service that is designed solely for EV chargers would also need to be sized for 125%. But how does one get to that conclusion via the NEC? 220.40 says.... Calculated load of a feeder or service shall not less than the sum of the branch circuits on the loads supplied, as determined by Part 2 of this article.


Example EV Charger Service has 530A of connected load. so... 600A service or 530A x1 25% = 662A (800A service)

Maybe I am making this more difficult than it has to be. Once you go down the rabbits hole......


Thanks for the replies!
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
This question seems to be getting more frequent. In my view the NEC is not clear on this. I'm not sure what the answer is. Let's see what others think.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
625.41 is clear that EVSEs are continuous loads for feeder and branch circuit sizing.

When a service has just one service disconnect/OCPD, that OCPD is protection for both the feeder and the service conductors. So per 215.3 that OCPD needs the 125% factor for continuous loads unless it is 100% rated. Then per 230.90(A), the service conductors will need to have an ampacity in accordance with that OCPD size.

[Although you get to use 240.4(B) on the service conductors per 230.90(A) Exception 2. So if the total load is 240A continuous, and you therefore need a 300A feeder/service OCPD, then for the service conductors it would suffice to provide conductors of ampacity 251A, allowing 300A protection per 240.4(B).]

When a service has two to six service disconnects/OCPD, then 230.90(A) exception 3 decouples the service conductor size from the OCPD size. So in that case, each OCPD would need to be sized for 125% of the continuous load it supplies, but the common service conductors would only need to be sized to 100% of the total continuous load.

[If the service conductors are split in a trough above multiple enclosures, that still leaves open how the segments to each service OCPD should be sized, but complying with 230.90(A) would make sense there to me.]

Cheers, Wayne
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
See 230.42 for services, or 215.2 for feeders.

I agree with texie that the code doesn't clearly spell out how one is to account for these requirements when following article 220. Perhaps one is supposed to just add the 25% to the nameplate of any continuous loads before one starts the 220 calcs. However there are some contradictions, such as where the optional methods (220.82-84) refer to nameplate rating of appliances.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I will add, in the case of a service solely for EV chargers, there isn't really anything of significance in 220 that changes anything so far as I have seen. So 230.42 is your requirement.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
See 230.42 for service
Thank you, I'm not sure how I overlooked the rule requiring service entrance conductors to be sized at 125% of the continuous load.

So I have to retract most of my previous answer. It would only apply to the service conductors between the service point and the service entrance conductors.

Cheers, Wayne
 

LibertyEngineering

Senior Member
Location
Allentown, PA
will add, in the case of a service solely for EV chargers, there isn't really anything of significance in 220 that changes anything so far as I have seen. So 230.42 is your requirement.
I get that for Service entrance conductors but is that to mean the ampacity of the service entrance conductors rules the OCPD size on the service?
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
In a nutshell, yes. Ampacity pretty much always rules OCPD. Generally you size conductors for the calculated current, then you protect them per 240.
Yes, with the proviso that the NEC rules for sizing conductors for the calculated current are based on the limitations of the OCPD that will ultimately protect them. So there's already a bit of "lookahead" in the algorithm for sizing the conductors.

Cheers, Wayne
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
Yes, and while I have no direct experience, the example in the OP does seem like a situation in which a 100% rated service OCPD might pay for itself in decreased conductor sizes.
Hmm, as 625.41 requires the feeder OCPD to be sized at 125% of the EVSE rating, with no exception for 100% rated OCPD, that wouldn't work. Seems like an oversight in Article 625.

Cheers, Wayne
 

retirede

Senior Member
Location
Illinois
Hmm, as 625.41 requires the feeder OCPD to be sized at 125% of the EVSE rating, with no exception for 100% rated OCPD, that wouldn't work. Seems like an oversight in Article 625.

Cheers, Wayne

I’m not sure it changes your answer, but the way I read the OP, he is asking about a DC charger installation, not EVSEs.

I can’t come up with a standard EVSE size that would extend to 530A. Unless he has 11 - 48A EVSEs and rounded up.
 

retirede

Senior Member
Location
Illinois
Look at the Article 625 definition of EVSE, isn't a DCFC still an EVSE?

Cheers, Wayne

You’re absolutely correct. I’ve never looked at the NEC definition before.

In the EV community, EVSE is generally reserved for AC supply equipment, while DCFC is the moniker for DC chargers. I gotta quit hanging out with those guys!
 
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