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We installed a 50 amp breaker and a new cable out to a new outlet, however only 8 amps come out, and the Tesla charges one-third as fast. The wire is 6 gauge, I’m in the US and the car is fine. The charger is the one which came with the car a Tesla model S 2014. and the car is showing 240V 8 amps, and charging 4 times slower than in my previous home

Does anybody know why we might be getting only 8 amps out?

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  • @MrSay -- what wiring method are those 8AWG wires in? A NM ("Romex") or UF cable? Some other type of cable? A conduit? Dec 13, 2020 at 0:37
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    I don't know the specifics, but as I understand it, there are a ton of settings and variants in a Tesla relating to charging. Two that come to mind are battery pre-heating and limits on charging rate when the battery is nearly full. Dec 13, 2020 at 18:01
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    (Although it's not quite OK for a NEMA 14-50 receptacle...) Dec 13, 2020 at 18:52
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    The receptacle box looks very dubious - like you could poke a finger into it and get a nasty shock - not to mention being the wrong sort of box for the way it's mounted. None of which has to do with your charging rate, but sloppy work in the extreme, which might well have to do with your problem in a roundabout way. The Way a QO box works (to my knowledge as the owner of several QO boxes) the breaker looks installed correctly, the gap above it does not mean it's not on one of the busses - doubles work in any position they fit in. Other makers vary on that.
    – Ecnerwal
    Dec 14, 2020 at 1:35
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    @Kris -- the breaker is fine save for being the wrong amp rating for the receptacle Dec 14, 2020 at 1:58

3 Answers 3

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only 8 amps come out, and the Tesla charges one-third as fast.

The electrical circuits in your home can't restrict the amount of current they deliver, other than to shut off completely if you exceed the threshold for the breaker by a certain amount over a certain amount of time. If you are getting any current at all, the only thing that could be limiting that current is whatever you have plugged into it.

In the case of electric vehicle supply equipment (EVSE), this would be either the charging station itself, or the settings in the vehicle. You appear to have the Tesla "Mobile" EVSE, which when attached to a 240V supply should provide much more than 8A of charging. However, it is compatible with both 240V and 120V, and the 8A is consistent with it being plugged into a 120V/15A supply; their documentation says it will charge at 3 miles/hour, which works out to about 1 kWh, which at 120V is about 8A.

Your photos don't show what kind of outlet you have, nor do you indicate where in the world you are located. But if, as the 50A (or 60A?) breaker suggests, the circuit is supposed to be supplying 240V, the first thing to check would be to make sure there is in fact 240V at the outlet; if not, then it has been wired incorrectly. You indicated in the comments that the car is telling you it's connected to a 240V supply, which I would think would be authoritative. But there's no harm in double-checking.

Of course, the other thing to check is the car's charging settings themselves. Many Tesla's include a "geo-fenced" configuration for charging, meaning you may get different charging rate settings in different locations (based on GPS). It's possible that in your new location, you haven't adjusted the maximum charging rate. Or maybe it just got set lower for some reason at some point.

Finally, keep in mind that the charging rate slows considerably when the battery is nearly empty or nearly full. You won't see the fastest charging rates under those conditions. Rates are also limited depending on battery temperature, but a) the Tesla actively manages battery temperature to minimize this effect, and b) from the photos it looks like you are probably charging in an enclosed area, so I wouldn't expect temperature to be a major concern.

I think it's highly unlikely that there's anything wrong with the EVSE or the car's charging components themselves. But if you've gone through and ruled out all of the possibilities above, it could be time to contact Tesla for support. It would be easy enough for you to take the EVSE to your local service center and have them verify it operates correctly, as well as have them check the car itself.

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Almost certainly you have (accidentally or on purpose) set the charge current limit to 8 A in your car's touchscreen panel. Touch the lightning bolt icon to get to the charging screen and reset the "max current limit" to 40 A and you should be fine, at least so far as the car itself goes.

The next thing: if in fact you have a 15A or 20A outlet and are using the 20A 3prong adapter, then the cable assembly will limit the current. If you are using the NEMA14/50 socket and adapter, and it's properly wired for 240VAC, then just resetting the car's limit will suffice. (I am an owner of a Model S and have done all these things)

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Actually, even simpler than that - if the trickle charger cord is not pushed all the way into the transformer (not the port), it will charge but limit the rate to 3 miles per hour or 8 amps. Make sure all connections are pushed in as far as possible (plug, transformer and adapter).

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