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If I only have a 50A main in my garage, can I get a Wall Charger and run it at 40A to charge?

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Looks like the highest you should go is 30 amp. Even though you have a 60 amp sub panel, the wires going to sub panel from the main have only a 50 amp breaker. In theory the 50 amp breaker will trip long before the 60 amp breaker in your sub panel ever does. So I would just think of your detached garage as 50 amp panel.


30 amp will give you a decent charge rate of about 22 miles added per hour, and not over burden your electrical system.

Get the Wall Connector if you want one. Another option is to install 14-30/10-30 outlet and get a second UMC (Less than $300 on eBay/forum) and leave that attached in you garage. Either way you can always have your original UMC in the car and with you.


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I think I could use 40A with the WC if I went that route? It would be 80% of the available 50A and since the only other things in the garage are:
  • circuit for 2 lightbulbs
  • circuit for 1 electrical outlet
  • circuit for 2 electrical outlets and garage door. Router is plugged into one of these outlets.
I don't have anything powerful in the garage so I would think it is safe to at least go to 40A?
 
I think I could use 40A with the WC if I went that route? It would be 80% of the available 50A and since the only other things in the garage are:
  • circuit for 2 lightbulbs
  • circuit for 1 electrical outlet
  • circuit for 2 electrical outlets and garage door. Router is plugged into one of these outlets.
I don't have anything powerful in the garage so I would think it is safe to at least go to 40A?
I would think a 40a breaker and charging at 32a would be ok.
 
My Gen3 wall connector's handle/cable started to melt on a NEMA 14-50 socket when set to 40 amps. Tesla EVSE warranty is bad. Sure it has a warranty, but after three tries to get an RMA I gave up. "We will email an RMA" == "Check is in the mail" x "I check my tire pressures before each drive".

Stick with Gen2 if you can find them, they are commercial duty. Gen3 is lightweight disposable tech.
 
Ok that makes sense. I have an electrician coming over so I can ask this to them as well but could I have a 45A breaker installed and charge at 40A using the Wall charger or would I need a 50A breaker, as per the Tesla website for 40A charging to work?

I don't think they make 45a breakers. The WC also doesn't have a setting for that size breaker.

You are supposed to charge at 80% of the breaker (and wiring) rating due to the continuous nature of charging. So a 40a circuit charges at 32a. 50a circuit would charge at 40a. It it would exist, a 45a charges at 36a (but, it doesn't exist).

I do not think a 50A breaker for the charger is appropriate given the 50A breaker and wiring to the sub-panel. Sure, you are only charging at 40a so there is some spare. But, when you are charging the circuits are all warm and, well, that's just not how it's speced.

Why is all this important? Power dissipated in a resistor (wire, breaker, etc) is a function of current squared. So when you drop from 40a current to 35a current, the heat generated in the circuit drops by 25%.
 
That is a really strange setup. The breaker in the main that feeds the garage subpanel is 50A. So then why is the subpanel's main cutoff a 60A? I didn't think that would be allowed, but I'm not sure of a code reference for that.

So with the subpanel really being 50A, and it having other circuits in it, you shouldn't do the whole 50A for the car charging circuit. I would probably say a 30A, like a 14-30 outlet. Really, don't be so dismissive of a 24A charging rate. But 40A might be OK too. From the chart @mrau posted, the Model 3 gets about 22 miles per hour recharged. (Y should be similar--maybe 21?) So in 8 hours overnight, you would get about 168 miles refilled. That's pretty solid.
 
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That is a really strange setup. The breaker in the main that feeds the garage subpanel is 50A. So then why is the subpanel's main cutoff a 60A? I didn't think that would be allowed, but I'm not sure of a code reference for that.

So with the subpanel really being 50A, and it having other circuits in it, you shouldn't do the whole 50A for the car charging circuit. I would probably say a 30A, like a 14-30 outlet. Really, don't be so dismissive of a 24A charging rate. But 40A might be OK too. From the chart @mrau posted, the Model 3 gets about 22 miles per hour recharged. (Y should be similar--maybe 21?) So in 8 hours overnight, you would get about 168 miles refilled. That's pretty solid.

All I can think of it is makes an inexpensive disconnect. It's never going to nuisance trip and the 50a back at the main is protecting the circuit. Really strange and could lead to misunderstanding of the capacity of the sub-panel. Hard to tell from the diagram, but the panel does look like it has a main bus... so why even bother bringing in power through a breaker?

It would probably also be worth checking the wire gauge from the main to the sub-panel and see if would support a larger breaker. Unlikely... but...

I'm also with you, don't underestimate a 30a circuit. Except for quick turnarounds the car will be full in the morning. I share 3 cars now on a 50a circuit and a single WC. I did buy a second WC, but it still sits in the box due to my laziness (and thriftiness)
 
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Hard to tell from the diagram, but the panel does look like it has a main bus... so why even bother bringing in power through a breaker?
I think that part is just a requirement of how you have to connect subpanels, where it needs to have breakers at those connection points. It has to have a breaker to split out from the main panel. And I think then the sub may also have to have its own "main" breaker.
 
Always good to have options.

Consider running an 8 gauge wire from sub-panel to the wall connector. That way you could use a 50 amp circuit if the sub-panel is ever upgraded to 100 amp. You could then install a Wall Connector and set it at 40 amp. If the circuit should happen to get too warm or cause tripping of breakers, then dial down the Wall Connector to 30 amp. Or just start with wall Connector at 30 amp and see if that fulfills your charging needs. It is a lot easier to change setting on wall Connector than to re-run a larger wire later.
 
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I think that part is just a requirement of how you have to connect subpanels, where it needs to have breakers at those connection points. It has to have a breaker to split out from the main panel. And I think then the sub may also have to have its own "main" breaker.
Of course everyone is different. I have two sub panels, one with 50a and one with 60a in the main panel. No main breaker in the sub-panel. I guess it's all up to magic, what year it was done, the electrician, and the AHJ.

Of course, the inspector blew off that the contractor had painted the inside of the sub-panels including the bus bars. So mine may not be the best example... grrrr...
 
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Of course everyone is different. I have two sub panels, one with 50a and one with 60a in the main panel. No main breaker in the sub-panel. I guess it's all up to magic, what year it was done, the electrician, and the AHJ.
Yeah, the first part I am more sure of--having to breaker off to feed a sub. But the sub may not really need its own main breaker.
 
I don't think they make 45a breakers. The WC also doesn't have a setting for that size breaker.

You are supposed to charge at 80% of the breaker (and wiring) rating due to the continuous nature of charging. So a 40a circuit charges at 32a. 50a circuit would charge at 40a. It it would exist, a 45a charges at 36a (but, it doesn't exist).

I do not think a 50A breaker for the charger is appropriate given the 50A breaker and wiring to the sub-panel. Sure, you are only charging at 40a so there is some spare. But, when you are charging the circuits are all warm and, well, that's just not how it's speced.

Why is all this important? Power dissipated in a resistor (wire, breaker, etc) is a function of current squared. So when you drop from 40a current to 35a current, the heat generated in the circuit drops by 25%.
This is such a helpful post. Thank you for expelling that to me!!
 
Always good to have options.

Consider running an 8 gauge wire from sub-panel to the wall connector. That way you could use a 50 amp circuit if the sub-panel is ever upgraded to 100 amp. You could then install a Wall Connector and set it at 40 amp. If the circuit should happen to get too warm or cause tripping of breakers, then dial down the Wall Connector to 30 amp. Or just start with wall Connector at 30 amp and see if that fulfills your charging needs. It is a lot easier to change setting on wall Connector than to re-run a larger wire later.
I think I'm going to go this route with getting the WC and seeing how it goes for 30A.
 
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Personally, I don’t think I’d set it at 40a (50a breaker) and watch if it gets warm. I’m not an electrician, but I think the electrician will recommend a 40a breaker which will charge at 30a.

If a licensed electrician is willing to permit the job and put in a 50a breaker with the WC set to 50a (charge at 40a) then go for it.
 
I think I could use 40A with the WC if I went that route? It would be 80% of the available 50A and since the only other things in the garage are:
  • circuit for 2 lightbulbs
  • circuit for 1 electrical outlet
  • circuit for 2 electrical outlets and garage door. Router is plugged into one of these outlets.
I don't have anything powerful in the garage so I would think it is safe to at least go to 40A?
My concern here, and I have experienced it. Is the garage door opener will likely trip you. Mine pulled a good 10 amps so the door and charger would put you at 50 amps and the lifts at like 52 which should trip your 50 amp breaker. So like others have suggested drop back to 32 amps or lower. I charge at 24 and ALWAYS have a full charge in the morning.
 
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Very True.



Now I'm unsure. I took a picture of my main breaker panel and it has two breakers labelled 50A that are connected and the sub breaker box in the garage has two 60A switches? So I think I may have 100A? I'm not sure. I should get an electrician to explain this so I understand a bit better.

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Your EV charger is on a 20a circuit, the entire panel is on a main 60a breaker.

The sum of all your circuits is 55a to keep it under the 60a limit.

As a general rule of thumb you want to keep your home charger below 80% of rated capacity so you want your home charger under 16a on that 20a circuit.

My home charger is on a 240v 50a circuit (the picture is on a dedicated 240v panel for my garage) and I have it capped at 40a of draw in the charger settings. If you want more safely you need to upsize the circuit.
 

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My concern here, and I have experienced it. Is the garage door opener will likely trip you. Mine pulled a good 10 amps so the door and charger would put you at 50 amps and the lifts at like 52 which should trip your 50 amp breaker. So like others have suggested drop back to 32 amps or lower. I charge at 24 and ALWAYS have a full charge in the morning.
Circuit breakers (contrary to what you would think) do not trip immediately when exceeding the rated current. Only a massive current spike will do that. E.g. drawing 52A on a 50A breaker might take an hour or so to trip.

Of course it's better not to knowingly exceed the rated capacity...
 
The weakest point in the link is the dual 50A breaker feed from your main panel to your sub panel. That being said, I would install 6 ga wire from the sub panel to your WC in case you one day decide to up the power into the sub panel which would then allow for full 60a charging of the WC.

The WC will draw a max of 40a once you set it to the 50a setting in setup, This leaves you 10a margin which IMHO is enough to power the door which is the highest draw. I would simply try it and see if it works but my guess is you will be fine. Worst case scenario is the breaker will pop and you then know it cannot handle both charger at the 50a setting and the door in operation at the same time. If this is the case then simply reconfigure the WC for 40a and you will be good to go.
 
Circuit breakers (contrary to what you would think) do not trip immediately when exceeding the rated current. Only a massive current spike will do that. E.g. drawing 52A on a 50A breaker might take an hour or so to trip.

Of course it's better not to knowingly exceed the rated capacity...
And while true I have OFTEN seen the opposite where a 50 amp breaker will trip at 48, 40 and even 35 amps. Just a single dedicated load.
 
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