Old 3 prong 40 amp Kiln outlet and circuit for Tesla charger?

[Feathermerchan]

The Tesla Gen 1 UMC (I have two of them) can support up to 40A (80% of 50A os 40A)which the LR model 3 and Y can also support. But due to problems when plugging it into a 14-50 wired to a 40A circuit, Gen 2 is only capable of 32A.
32A is 80% of 40A. My circuits are wired for 50A and use 50A breakers. I have the cars turned down to 30A but I can go as high as 40A.

 

[arnolddeleon]

If you install a 14-50 which is a 50A outlet, Per code I think you must install wire and breaker for 50A. This is so someone does not come along and plug a 50A load into the 50A socket and think its OK.
So I would buy a 50A breaker and 6 ga wire. The ground wire can be 8 ga.

Not true and I see @Rocky_H beat me to it. This is a common misconception. It happens to be made necessary by the non-existence of 40A receptacle. If the user makes a mistake, blindly assumes that the 50A receptacle implied a 50A breaker, and over draws it, the right thing will happen, the over current device will trip protecting the wire (which is presumably the weak link). BTW there is reverse exception to this, a 15A receptacle is allowed on a 20A circuit, that's because receptacle specifies that you shouldn't draw more than 15A.

 

[Rocky_H]

BTW there is reverse exception to this, a 15A receptacle is allowed on a 20A circuit, that's because receptacle specifies that you shouldn't draw more than 15A.

We are really getting off into the weeds here, but these situations and conditions are a little interesting. Two different scenarios. This one you are talking about is for multiple outlet circuits, and yes, they specify that you can have a mix of 20 and 15 amp outlet types on a 20A rated circuit.
But the section that guides a dedicated circuit with only one single outlet on it says the breaker must not be higher rated than the outlet.

 

[selaing]

Thanks all. since the outlet is so close to the box, I could get it all changed out with the 50 and 6/3. My friends electric inspector for his house asked why you need a 50 amp breaker when only pulling 32.
I want to do what is "correct and best" for my future car.

 

[qdeathstar]

You're right, but so what? The outlet has to be wired per code regulations, without regard to what gets plugged in and how that appliance makes use of the power available to it.

the so so what is, I would not recommend a homeowner who is unfamiliar with tools to make a change that basically is of little benefit to him and may result in fire or loss of path to ground (if he improperly connects the new wires while he changes the outlet). Leave it be is my recommendation, unless ofc he is getting a liscensed electrician to do, then by all means. But peeps was suggesting DYI....

 

[qdeathstar]

it can be carrying current on the neutral and can have some different potential at that point.

Nah, I highly doubt it. It’s theoretically possible I suppose, in a worse case scenerio, but very unlikely. And certainly it would not affect the ability to the breaker to trip in the event of short circuit to case, which is what the ground is for.

 

[wws]

Nah, I highly doubt it. It’s theoretically possible I suppose, in a worse case scenerio, but very unlikely. And certainly it would not affect the ability to the breaker to trip in the event of short circuit to case, which is what the ground is for.

Way more than theoretical. I've measured such discrepancies in my own house. Granted, and fortunately, in the millivolt range, but still there.

 

[qdeathstar]

Way more than theoretical. I've measured such discrepancies in my own house. Granted, and fortunately, in the millivolt range, but still there.

Way more than theoretical. I've measured such discrepancies in my own house. Granted, and fortunately, in the millivolt range, but still there.

Describe to me the method you used to measure voltage differential between the neutral of your sub panel and main service disconnect....

 

[DCGOO]

When we bought our house over 10 years ago, the prior own had a kiln in the garage. This kiln was on a 40 amp separate outlet with a leviton 3 prong outlet.
Now, coming to today.... I am seriously looking at a Tesla and wonder for my house charger, can I just use this circuit and plug? Or should I re-wire and put a bigger plug. The outlet and panel are about 24 inches apart.
Thanks in advance for your advice.
Cheers
Stuart

Since your panel is so close, you could simply remove everything and install a Tesla Wall Connector, hard wired. IOW, no outlet at all. Would give you the full 48 amps charge rate. This is possible to DIY in an afternoon, or if you hire an electrician it shouldn't take more than a couple of hours.

 

[wws]

Describe to me the method you used to measure voltage differential between the neutral of your sub panel and main service disconnect....

Measuring at a receptacle with my trusty Fluke multimeter.

 

[qdeathstar]

Measuring at a receptacle with my trusty Fluke multimeter.

how does that get you the voltage difference between the neutral at main panel and the subpanel? Surely you would have to measure across the wire....

Protip: If you are going to bullshit, just say you calculated it. The measurement with a meter is going to produce all kinds of errors, because there is going to be resistance you need to account for in your test setup.

just measure the current draw of the subpanel, measure the distance of the wire, note the size of the voltage, and measure the voltage at the main panel and then you can calculate the voltage differential.

 

[wws]

how does that get you the voltage difference between the neutral at main panel and the subpanel? Surely you would have to measure across the wire....

Protip: If you are going to bullshit, just say you calculated it. The measurement with a meter is going to produce all kinds of errors, because there is going to be resistance you need to account for in your test setup.

just measure the current draw of the subpanel, measure the distance of the wire, note the size of the voltage, and measure the voltage at the main panel and then you can calculate the voltage differential.

I don't need to BS.