Is 40 amp breaker ok to up a 14-50?

kyrral

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#1
The Mobile charge only draws 32 amp I think so this should be ok? I've already got one and don't have to show for an antiquated Sisco 50amp. Someone else told me that upon start up the circuit would draw more than 32 amps so I needed a cushion in regards to the breaker. Is this true?
 

Ct200h

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#2
It wouldn’t meet code but seems like it would work. Lots of people might be trying the same thing as I have charger on a 40 amp breaker , I may remove the ea,l charger and install a 50 amp outlet for my umc and Marie the outlet 40A
 

MelindaV

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#4
it also may become an issue if selling the house and someone expects to be able to use the 14-50 receptacle as a 50A power source.

I think (could be mistaken) you can undersize the breaker by code, just not put in a larger breaker than the receptacle can handle. (I think in Canada, the code actually downsizes the breaker, so the 40A is standard for a 14-50 up north).
 

JasonF

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#5
The capacity of the circuit breaker should be low enough to protect the size of wiring to the outlet. That’s it’s primary purpose, to protect the wiring. It should also not be larger than the capacity of the outlet. You should look up your local electrical code to figure out the appropriate circuit breaker capacity for your wiring size, or contact an electrician if you’re not sure.

Even 32 amps of 220 volts is enough to cause a serious fire if the breaker is too large for the wiring, especially with a Telsa Mobile Connector, which will pull as much amperage as the circuit will allow.

That said, if your wiring will support 50 amps, you can certainly put a 40 amp breaker on it.
 

Frank99

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#7
In a weird exception, it is perfectly acceptable in the NEC to install a 14-50 receptacle on a 40 Amp circuit. The main reason for this is that there's no approved outlet for a 40A circuit. See: https://diy.stackexchange.com/quest...ok-to-use-a-50-a-receptacle-on-a-40-a-circuit
If you've ever wondered why the Gen II UMC is limited to 32A, rather than 40A like the Gen I, this is it. The UMC knows that it's plugging in to a 14-50 receptacle, but it can't know whether the circuit is rated for 40A or 50A so Tesla has to assume a 40A circuit.

As an aside, The NEC limits the current for a continuous load (like EV charging) to 80% of the circuit capacity - 80% of 50A is 40A (the Gen I UMC), and 80% of 40A is 32A (the Gen II UMC).
 

garsh

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#8
In a weird exception, it is perfectly acceptable in the NEC to install a 14-50 receptacle on a 40 Amp circuit. The main reason for this is that there's no approved outlet for a 40A circuit.
It's also "safe" to use a lower-amperage breaker. It will still accomplish the goal of making sure the wires don't overheat from too much current.