What size circuit should I use for Tesla HPWC?

[dk10438]

Hi,
I'm in the process of getting a Tesla HPWC installed and I was looking at the recommended circuits and for the P100D it recommends a 60 A circuit? My car has the 72A charger so I was thinking that a 90A circuit breaker would allow me to charge at 72A. A 60A breaker would only allow me to charge at 48A? I was actually planning on either a 70A or 80A breaker to allow me to charge at 56A or 64A respectively. Can someone help??

 

[davewill]

Any of those will work. It's a matter of balancing the cost of installation with your individual charging needs. If putting in a 90a circuit is going to bump the install up a lot, that would be a factor. If you're doing a 30 mile daily commute, 50a would be plenty. OTH, if your daily commute is 150 miles, you might want to go a big as possible.

For example, I've been driving electric for 8 years on a 40a circuit (30a EVSE). It works for me. I'm finally adding a Model 3 to the stable, so I'm also adding a new 50a circuit for the second car. Ironically, the M3 is getting the old 30a EVSE, and my Rav is the one that will get the new 40a EVSE because it can actually charge at 40a, unlike the M3.

 

[ucmndd]

There’s no right answer. If you want the max available speed your car can accept, then 90A is the way to go (Tesla website recommendations are based on current cars that no longer have the 72A charger option).

 

[dk10438]

Got it! I had a feeling those recommendations were based on the newer cars that didn't have the larger charger. I'll probably elect to go with an 80A circuit .

 

[boaterva]

Only other consideration would be would you ever want the option of two HPWCs to share the circuit? Then you might want to install 100 A (80 usable) now. See my signature for Flasher’s excellent FAQ and a link to an installation thread on HPWCs.

 

[P85_DA]

Hi,
I'm in the process of getting a Tesla HPWC installed and I was looking at the recommended circuits and for the P100D it recommends a 60 A circuit? My car has the 72A charger so I was thinking that a 90A circuit breaker would allow me to charge at 72A. A 60A breaker would only allow me to charge at 48A? I was actually planning on either a 70A or 80A breaker to allow me to charge at 56A or 64A respectively. Can someone help??

If u have the capacity put the 90 ..incremental cost over a 70 or 80 breaker ..I have same setup P100 with 72a Charger ...I have a 100am breaker ..I normally charge at 64 but having the option to bump up as needed is nice

 

[BlueOvalFan]

Can someone help??

If your car can charge at 72A I’d set it up for that...never know when you might want to charge at full capacity. Better to have it and not need it, than the other way around....

Breaker would be; 72amp * 125% (>3hr load) = 90amp

Wire should be either #2 gauge Romex, or #3 guage THW or equivalent per the linked chart

Also, wire should be derated if your ambient temperature is in excess of 86-degrees F and/or your voltage drop calc exceeds 3%.

 

[dk10438]

hmm, electrician said the #4 could be used for 80 or 90A? it's a short run, 5 ft. Does that matter?

 

[P85_DA]

hmm, electrician said the #4 could be used for 80 or 90A? it's a short run, 5 ft. Does that matter?

#4 THHN or THWN should be fine for that

 

[dk10438]

thanks!

 

[BlueOvalFan]

hmm, electrician said the #4 could be used for 80 or 90A? it's a short run, 5 ft. Does that matter?

Yes, it seems the #4 running at a planned 72A load can be factored and designed as a 90A circuit. So it’s important to understand what insulation type he’s using. It needs to be THWN-2, THHN, XHHW-2, USE-2 per the linked wire chart above. If it’s anything else (Romex NM-B, UF-B, THW, THWN, SE, USE, XHHW) you’ll be in trouble if you use it at 72A.

Please be careful here. Make sure he’s aware this is for an EV, and your actual operating current will be subjected to long load times and needs the wire guage type and insulation to be installed per NEC.

Why don’t you ask him for the specifics to ensure you are getting what you are expecting.

I can share with you many a story of a professional engineer, or lic contractor designing or installing non-compliant materials. Caveat emptor...!

#4 THHN or THWN should be fine for that

I’m not following on the #4 THWN recommendation—that’s only rated for: 85A(.80)=68A when loaded for 3 hour and longer durations. It won’t be usable if he wanted to change breakers and run above 68A.

I think there is always confusion between short and long duration demands that just spouting it can handle an amperage is misleading, such as the contractor did. One needs to know the why behind the comment it can handle 90A; based on what loading condition and code section...? And what is the wire insulation type...?

 

[tga]

Breaker would be; 72amp * 125% (>3hr load) = 90amp

I think there is always confusion between short and long duration demands that just spouting it can handle an amperage is misleading, such as the contractor did. One needs to know the why behind the comment it can handle 90A; based on what loading condition and code section...? And what is the wire insulation type...?

NEC 625.21 (2011) or 625.41 (2017) requires all EV charging circuits to be upsized by 25%; ie, you must treat all EV charging as a continuous load, regardless of charge session duration. It doesn't matter if you're only charging for 1 hour or 10.

Yes, it seems the #4 running at a planned 72A load can be factored and designed as a 90A circuit. So it’s important to understand what insulation type he’s using. It needs to be THWN-2, THHN, XHHW-2, USE-2 per the linked wire chart above. If it’s anything else (Romex NM-B, UF-B, THW, THWN, SE, USE, XHHW) you’ll be in trouble if you use it at 72A.

You can't use the 90C #4 copper rating with the HPWC, since both the HPWC and your circuit breaker will have 75C terminals. If you use #4 copper, you're limited to an 80A breaker and 64A charging. If you want to charge at 72A, you must use a 90A/75C circuit, which means #3 or larger (which is good for 100A/80A charging).

 

[BlueOvalFan]

NEC 625.21 (2011) or 625.41 (2017) requires all EV charging circuits to be upsized by 25%; ie, you must treat all EV charging as a continuous load, regardless of charge session duration. It doesn't matter if you're only charging for 1 hour or 10.

You can't use the 90C #4 copper rating with the HPWC, since both the HPWC and your circuit breaker will have 75C terminals. If you use #4 copper, you're limited to an 80A breaker and 64A charging. If you want to charge at 72A, you must use a 90A/75C circuit, which means #3 or larger (which is good for 100A/80A charging).

I don’t have a HPWC so I couldn’t comment on the requirements but this more or less illustrates my point—the contractor without knowing the specifications is in stalling a circuit without understanding how the system works as a whole. Why would he say it’s good for 80A - 90A and recommend #4s for an EV circuit...!?

The breakers in my panel are limited to 75C as well hence why I originally referenced #3 THW. I assumed if #4 were being installed as the OP indicated it was already vetted. Glad you were able to clarify for him...

 

[brkaus]

Simply a cost decision. In many jurisdictions, going over 60a you also need a local disconnect which adds to the price.

 

[tga]

The breakers in my panel are limited to 75C as well hence why I originally referenced #3 THW. I assumed if #4 were being installed as the OP indicated it was already vetted. Glad you were able to clarify for him...

I've looked for residential breakers with 90C terminals just to see if I can find one. I don't think they exist (75C max). In theory, I suppose you could connect a short run of #3 to a run of #4 with 90C insulation with a pair of 90C rated polaris connectors, but that seems super-hacky. Plus, the OP said it's only a 4-5 foot run, so the cost of #4 vs #3 is negligible.