Tesla Charger on a heavily loaded 200A service BUT w/ Tesla power wall units...

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CustomElectricLLC

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Midlothian Texas
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Electrical Contractor
Doing load calculations for a service where a client wants a Tesla power connector charger installed. Service is 200A w/ a 2, 3, and 5 ton unit ac/heat pump units with 5-10kw heat strips in AHU's and is roughly 4k sq ft. I ran all the numbers and with standard method Im slightly above 200 amps (208 amps I believe). Its a rough guesstimate because I can't go through everything in the whole house but definitely most concerning loads are all those heat pumps units on such a smaller service size. I figured the EV charger at 100% in my load calcs but the customer also has Tesla solar and (2-3) power wall units. Looking at the specs to PW units have a 11kw resistive/98A LRA max or ≤32A RLA output (for motors) capability. Can anyone shed some light on if I can figure this extra available capacity into the load calculation and perhaps be in the green for the install? First time I ran into something like this. Had it not been for the power wall Id tell customer he needs a service upgrade period. Thank you
 
retirede said:
If you’re only 8A over, set the hardware limit on the wall connector (EVSE) to 40A instead of 48A (reduces the number for load calc from 60 to 50) and you should be good.
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Customer is getting a model that accepts the fastest charge rate. I know my question isn't straight forward, because at the end of the day current demand through the main breaker and bus rating is what really limits the service size. But since it has an additional power source that has on demand power available to suppress a spike in demand I feel like future code cycles really should start addressing these thing in load calculations etc.
 
Keep in mind that in reality a 200 amp service like this will probably never see more than 100 or 125 amps worst case. I would not worry if the calculation came out 8 amps over. Unless you have to turn the load calculations over to the building department when you get a permit.

Then you might have to get creative. I think the code is going to have to look at some of this stuff in a more realistic way. I'm not sure how that can happen though.
 
petersonra said:
Keep in mind that in reality a 200 amp service like this will probably never see more than 100 or 125 amps worst case. I would not worry if the calculation came out 8 amps over. Unless you have to turn the load calculations over to the building department when you get a permit.

Then you might have to get creative. I think the code is going to have to look at some of this stuff in a more realistic way. I'm not sure how that can happen though.
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I agree with you, Ive looked at multiple peak load demands from homes similar to this scenario and I think 100A was max through 12mo period. The NEC really needs a look over on how we approach load calc because everything is getting more and more efficient. Thank you for the response
 
CustomElectricLLC said:
I agree with you, Ive looked at multiple peak load demands from homes similar to this scenario and I think 100A was max through 12mo period. The NEC really needs a look over on how we approach load calc because everything is getting more and more efficient. Thank you for the response
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If you have a year's worth of data from the smart meter, you should be able to look at what your maximum actual load was and start from there when you add a load rather than having to calculate it from scratch.
 
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