NEC requirements for multiple EV charging units

[Elisha]

Hello,
I am new to the community - so I wanted to say hi first I am from Germany and have extensive experience in battery storage and renewable integration, but am a little less familiar with US national electric code and rules.

I would like to get your feedback on the following scenario:

• Desire to build a site with electric vehicle charging units (10 units with ~50kW each)
• Utility can only allow a maximum power draw of 500kVA at the site
• An energy management system (EMS) will limit the total power drawn by all charging stations to 500kW - this energy management is not complying with any standards however and might fail (it is a prototype)

Question: Does the NEC allow (or not forbids me) me to just install a main breaker at the utility interconnection with a rating <=500kVA so that if my EMS fails the main breaker will trip (=my problem only) and the utility is protected from any overcurrent?
I was only able to find information about requirements for a reliable EMS, but not for an unreliable EMS with a main breaker as backup as suggested above.

I know that I need to talk to the utility before moving forward, but I wanted to get your feedback first and be prepared for the discussion with electrical engineers & the utility.

I appreciate your feedback.

 

[jaggedben]

I believe the answer to your question is yes, the NEC allows that. See 625.42, there is some language that speaks to this there.

I don't see any clear requirement that the energy management system be listed.

 

[Elisha]

Thank you for your feedback. I understand that in order to size the overall breaker smaller, 625.42 requires an EMS in accordance with 750.30.
The on-site EMS does not comply with 750.30 however (e.g., since it might fail and does not auto-shutoff the chargers in that case).

This exact reason is why I would like to use a breaker as physical limitation as backup for a potentially unreliable EMS in order to avoid any utility overload.

 

[David Castor]

625.42 is referring to feeders and branch circuits, not services. If you run 10 separate branch circuits with each sized for the load of each charger, then I think the main breaker could be sized based on a max load of 500 kVA. Keep in mind that the serving utility's electrical system and their transformer sizing is NOT covered by the the National Electrical Code. It's extremely common to have a "400 A service" served by a utility transformer that can provide only 200 A.

If you are wanting to put multiple charging stations on a single feeder, then 625.42 would apply to that feeder, in my opinion.

So the EV chargers are the only loads on this utility service?

 

[Elisha]

625.42 is referring to feeders and branch circuits, not services. If you run 10 separate branch circuits with each sized for the load of each charger, then I think the main breaker could be sized based on a max load of 500 kVA. Keep in mind that the serving utility's electrical system and their transformer sizing is NOT covered by the the National Electrical Code. It's extremely common to have a "400 A service" served by a utility transformer that can provide only 200 A.

If you are wanting to put multiple charging stations on a single feeder, then 625.42 would apply to that feeder, in my opinion.

So the EV chargers are the only loads on this utility service?

Thank you! Indeed, I was planning to use separate breakers for each single electric vehicle charging station connected to a panel. I might want to install a battery system as well and of course the panel needs to be sized accordingly.

Referencing your statement "the serving utility's electrical system and their transformer sizing is NOT covered by the NEC": Do you know if there are other references relevant for my case? (not specific to a certain utility, but nationwide)

The utility communicated a "500kVA" service that can continuously provide these 500kVA already. I am just looking for some reference whether my proposed solution with the "breaker protection against overload" is something the utility must accept (or can reject) based on some standards.

 

[jaggedben]

625.42 is referring to feeders and branch circuits, not services. ...

I don't know which code cycle you might be referring to but in the 2020 and 2023 NEC services (and feeders) are explicitly referred to in that section.

It should probably be noted that there are major changes to both 625 and 750 in the ladt code cycle or two. So the applicable code may matter a lot. My first comment above was looking at the 2020 NEC and is not correct for the 2023. (Apologies for any confusion.)

 

[jaggedben]

...
The utility communicated a "500kVA" service that can continuously provide these 500kVA already. I am just looking for some reference whether my proposed solution with the "breaker protection against overload" is something the utility must accept (or can reject) based on some standards.

The utility will not be looking to the NEC on this. But the local building department will. This may be a situation where you want to declare the facility to be an experimental laboratory or some such so that NEC standards do not need to be enforced on equipment that is installed to be tested. In any case, you ought to be able to install a 500kVA service if you ask for it and pay any costs you owe for it. To me that is a separate question from whether your unlisted EMS is code compliant.

 

[Elisha]

NEC 2023:
625.42 Rating. The power transfer equipment shall have sufficient rating to supply the load served. Electric vehicle charging loads shall be considered to be continuous loads for the purposes of this article. Service and feeder shall be sized in accordance with the product ratings, unless the overall rating of the installation can be limited through controls as permitted by 625.42(A) or (B).

So if I understand the NEC correctly, I am not allowed to choose any other option than 625.42 A (working load management, no prototype) or B (adjustable setting at the charging station)?
Installing a breaker to limit overall power drawn does not fall under these two options - the Service would be therefore not be "sized in accordance to the product ratings".

Am I missing something, or is there any other paragraph helping me out there?

 

[jaggedben]

You said you have 10 units at 50kW each. So if you have a 500kW service, the EMS or adjustable settings are not required by the NEC. So I actually don't see the issue there, unless you made a typo there.

I think it is correct under the 2023 NEC that limiting power draw with a main overcurrent device alone is not allowed if the sum of EVSE nameplate exceeds the service. I think the assumption is that the service may supply other loads or that no one may be monitoring it if the main overcurrent device trips, and the code endeavors to avoid nuisance trips. So if you made a typo above and your potential draw is actually larger than the service, I think the only option is to get some kind if special dispensation for an experimental facility.

 

[Elisha]

You said you have 10 units at 50kW each. So if you have a 500kW service, the EMS or adjustable settings are not required by the NEC. So I actually don't see the issue there, unless you made a typo there.

I think it is correct under the 2023 NEC that limiting power draw with a main overcurrent device alone is not allowed if the sum of EVSE nameplate exceeds the service. I think the assumption is that the service may supply other loads or that no one may be monitoring it if the main overcurrent device trips, and the code endeavors to avoid nuisance trips. So if you made a typo above and your potential draw is actually larger than the service, I think the only option is to get some kind if special dispensation for an experimental facility.

Yes, I made a typo - the total unit load >> utility load (20 units instead of 10 with 50kW each, 500kVA utility interconnection).....

Thank you for your valuable feedback. This is very unfortunate to hear that I am not allowed to limiting the power that way

 

[jaggedben]

Many states aren't on the 2023 NEC yet. Despite its name the NEC is not uniformly adopted across the US. If you are in a state on the 2020 NEC, I don't see the requirement that the EMS be listed. Maybe I missed it, but I think under that under earlier codes your experimental EMS doesn't have to be tested to be compliant. Kind of a funny argument, but that's what I see.

 

[David Castor]

I don't know which code cycle you might be referring to but in the 2020 and 2023 NEC services (and feeders) are explicitly referred to in that section

I was looking at the 2020 version. But I see now that services are referenced on the following section. Seems a bit confusing, but sorry for adding to it.

 

[Elisha]

Let's see what the utility says.....it really seems like it depends on their individual feedback and I don't have any "right to do so according to NEC"

 

[jaggedben]

Admittedly I've never negotiated the installation of a 500kVA utility service but I still don't see how it's up to them what you do on the load side of the service disconnect.

 

[brycenesbitt]

I was only able to find information about requirements for a reliable EMS, but not for an unreliable EMS with a main breaker as backup as suggested above.

The NEC is just gingerly stepping into EVLMS

NEC 750.30 ….
Load Shedding Controls. An energy management system shall not override the load shedding controls put in place to ensure the minimum electrical capacity for the following:

1. Fire pumps
2. Emergency systems

750.30(C)(2) automatically cease current flow upon failure or malfunction.