FlasherZ
Member
- Location
- Southern IL (near STL), USA
Hi all,
I'm looking for educated opinions for a newer type of electric vehicle charging network that is becoming available. Get your code books ready, follow along, and let me know what you think! First some background, and then the question of the day:
Previously, when you had two electric vehicles, each piece of Electric Vehicle Supply Equipment (EVSE, see NEC 625) operated independently. You needed to have a separate branch circuit for each of them and you had to count both of them in the load calc because they could both be charging at once. I've heard of a couple of inspectors agree to allow two units to be considered as one due the noncoincident loads provision (220.62) when two cars in a household were programmed to charge at different times such that it was "unlikely" (wording from 220.62) that they would charge at the same time, but I've also heard of some that disagreed with that interpretation without a more systemic way to guarantee they wouldn't be charging (A-B switches, etc.) One of those interpretation things, I guess...
Anyway, Tesla released a new EVSE unit yesterday. This unit has the ability to talk to up to 3 other "slave" EVSE units and coordinate the charging current between them so that together, they don't exceed the maximum charge rate configured on the "master" unit. This would seem to align with the NEC's section on automated load management (625.41) which says "Where an automatic load management system is used, the maximum [EVSE] load on a service and feeder shall be the maximum load permitted by the automatic load management system" - this is a big win for homeowners anticipating multiple EV's who don't have the need to guarantee full-rate charging at once and gets rid of the uncertainty about the noncoincident loads provision I spoke of, above.
These units provide 80A of charging current at their highest setting, and when applying the continuous load provision from 625, this means the branch circuit and load calculations need 100A.
I think the optimal way to install these would be to place a subpanel in the garage, fed by a 100A rated feeder connected to a 100A breaker in the service panel, and then 4 individual 100A branch circuits for each of the units in that subpanel. This feeder oversubscription would seem to be legal based on both the load management capabilities of the EVSE units (625.41) and the noncoincidental loads provision (220.62).
Another piece of background information that might help you when we get around to the question is 210.17: "An outlet(s) installed for the purpose of charging electric vehicles shall be supplied by a separate branch circuit. This circuit shall have no other outlets." (I acknowledge the proper meaning of "outlet" as used within the Code.)
So here comes the question:
Some people have been asking me whether they could forego the subpanel with multiple breakers due to the higher cost (~$250). In your opinion, would it be legal to create a 4-way tap (say with Polaris connectors or a multi-lug bus bar of some type) from a single branch circuit to feed all four units? Assume the units are designed such that it is practically impossible for multiple units to draw a combined current greater than that configured on the master for the circuit. I understand the downside - any maintenance takes all EVSE charging equipment offline, but in a home that's usually acceptable.
NEC 625 also requires that there be a "readily accessible" disconnect if the EVSE exceeds 60A or more than 120V from ground (e.g. 277V or greater). So there might already be a disconnect available to put these connectors in place. However, I've seen some inspectors agree that in a home where you wouldn't find locked doors between you and the service panel that the breaker in the service panel can be considered "readily accessible" to meet the requirements. They haven't considered EVSE to be a "fixed appliance" requiring the line-of-sight disconnect. That's another one of those I've seen open to interpretation; most electricians I've heard from have told the homeowner it was a good idea anyway to have a line-of-sight disconnect for safety.
I would attach the installation guide, but it's a whopper of a file. I've made it available here:
https://drive.google.com/open?id=0B395ZvZnO6KiX2xrck1kZGNCZnc
I'm looking for educated opinions for a newer type of electric vehicle charging network that is becoming available. Get your code books ready, follow along, and let me know what you think! First some background, and then the question of the day:
Previously, when you had two electric vehicles, each piece of Electric Vehicle Supply Equipment (EVSE, see NEC 625) operated independently. You needed to have a separate branch circuit for each of them and you had to count both of them in the load calc because they could both be charging at once. I've heard of a couple of inspectors agree to allow two units to be considered as one due the noncoincident loads provision (220.62) when two cars in a household were programmed to charge at different times such that it was "unlikely" (wording from 220.62) that they would charge at the same time, but I've also heard of some that disagreed with that interpretation without a more systemic way to guarantee they wouldn't be charging (A-B switches, etc.) One of those interpretation things, I guess...
Anyway, Tesla released a new EVSE unit yesterday. This unit has the ability to talk to up to 3 other "slave" EVSE units and coordinate the charging current between them so that together, they don't exceed the maximum charge rate configured on the "master" unit. This would seem to align with the NEC's section on automated load management (625.41) which says "Where an automatic load management system is used, the maximum [EVSE] load on a service and feeder shall be the maximum load permitted by the automatic load management system" - this is a big win for homeowners anticipating multiple EV's who don't have the need to guarantee full-rate charging at once and gets rid of the uncertainty about the noncoincident loads provision I spoke of, above.
These units provide 80A of charging current at their highest setting, and when applying the continuous load provision from 625, this means the branch circuit and load calculations need 100A.
I think the optimal way to install these would be to place a subpanel in the garage, fed by a 100A rated feeder connected to a 100A breaker in the service panel, and then 4 individual 100A branch circuits for each of the units in that subpanel. This feeder oversubscription would seem to be legal based on both the load management capabilities of the EVSE units (625.41) and the noncoincidental loads provision (220.62).
Another piece of background information that might help you when we get around to the question is 210.17: "An outlet(s) installed for the purpose of charging electric vehicles shall be supplied by a separate branch circuit. This circuit shall have no other outlets." (I acknowledge the proper meaning of "outlet" as used within the Code.)
So here comes the question:
Some people have been asking me whether they could forego the subpanel with multiple breakers due to the higher cost (~$250). In your opinion, would it be legal to create a 4-way tap (say with Polaris connectors or a multi-lug bus bar of some type) from a single branch circuit to feed all four units? Assume the units are designed such that it is practically impossible for multiple units to draw a combined current greater than that configured on the master for the circuit. I understand the downside - any maintenance takes all EVSE charging equipment offline, but in a home that's usually acceptable.
NEC 625 also requires that there be a "readily accessible" disconnect if the EVSE exceeds 60A or more than 120V from ground (e.g. 277V or greater). So there might already be a disconnect available to put these connectors in place. However, I've seen some inspectors agree that in a home where you wouldn't find locked doors between you and the service panel that the breaker in the service panel can be considered "readily accessible" to meet the requirements. They haven't considered EVSE to be a "fixed appliance" requiring the line-of-sight disconnect. That's another one of those I've seen open to interpretation; most electricians I've heard from have told the homeowner it was a good idea anyway to have a line-of-sight disconnect for safety.
I would attach the installation guide, but it's a whopper of a file. I've made it available here:
https://drive.google.com/open?id=0B395ZvZnO6KiX2xrck1kZGNCZnc
