Stupid Question - NEMA 14-50 on 100amp circuit

[xAGENTx]

Hello, I'm picking up my MX P90DL tomorrow. I just upgrade the service as my house over the weekend but the job isn't complete because my electrician is doing it after hours / on the weekend.

Today we wired a NEMA 14-50 to a temporary location. It is on a 100 amp breaker with 200amp Main service wires feeding it. We used this as a temporary solutionbecause the wire was on site and my electrician won't be back until end of the week.

It is my understanding that even if there is more power available, the car will adjust the power it pulls based on the connection. Is there any risk of damaging the car based on this set up? Should I manually reduce the charge rate to a lower amperage?

Thanks for the advice!

 

[xAGENTx]

Just to clarify, the wires feeding the plug from the breaker are the same large gauge wires we used for the service upgrade... again temporary solution because it is what we had on site.

 

[Canuck]

The UMC can only put out 40 amps, and your car can only draw 40 amps max using the UMC so you are fine. You only need to dial down the amps if the connection is undersized. You are oversized so there's no concern.

 

[xAGENTx]

Thanks. That's what I figured. My car has the high amperage charger but I'm guessing that doesn't matter for this situation because I'll still be using the UMC and not a wall connector.

 

[Canuck]

Thanks. That's what I figured. My car has the high amperage charger but I'm guessing that doesn't matter for this situation because I'll still be using the UMC and not a wall connector.

That's correct. The high amp charger will be great for your HPWC and other chargers capable of delivering up to 72 amps. Superchargers and CHAdeMO (if you have the adapter) bypass your onboard charger so they don't make a difference.

 

[Rocky_H]

Hello, I'm picking up my MX P90DL tomorrow. I just upgrade the service as my house over the weekend but the job isn't complete because my electrician is doing it after hours / on the weekend.

Today we wired a NEMA 14-50 to a temporary location. It is on a 100 amp breaker with 200amp Main service wires feeding it. We used this as a temporary solutionbecause the wire was on site and my electrician won't be back until end of the week.

It is my understanding that even if there is more power available, the car will adjust the power it pulls based on the connection. Is there any risk of damaging the car based on this set up? Should I manually reduce the charge rate to a lower amperage?

Thanks for the advice!

I first found where you posted this question in another thread:
https://teslamotorsclub.com/tmc/posts/1828922/
I'm a little disappointed that no one here noticed or commented on the big aspect of this--a 100A breaker "protecting" (not protecting) a 50A rated outlet. That is a code violation and very dangerous.

 

[TexasEV]

It's not a stupid question, it's a stupid and dangerous installation. The 14-50 outlet needs to be on a 50A breaker. Otherwise why even bother with a breaker at all?

 

[Electric700]

It's not a stupid question, it's a stupid and dangerous installation. The 14-50 outlet needs to be on a 50A breaker. Otherwise why even bother with a breaker at all?

I would say instead that this a situation where you should be very cautious, xAGENTx. As such I recommend that until the electrician can come back to install the 50 A breaker, you manually adjust the current to a lower value using the center screen and monitor the car while it charges. Anytime you make changes to your electrical setup in the future, it would be wise to monitor the circuit and charging progress for at least the first few charge cycles.

 

[DarkMatter]

The over current protection device is over sized for the outlet. You cannot safely use this to charge. I'm certain you have a regular 110v outlet with the correct size breaker on it. Use that until you're done.

You're getting this inspected, right? If your "electrician is doing it after hours / on the weekend" they still have to pull a permit. If this work causes a fire and there was no permit or inspection your homeowner's policy may deny the claim.

 

[ptsagcy]

The over current protection device is over sized for the outlet. You cannot safely use this to charge. I'm certain you have a regular 110v outlet with the correct size breaker on it. Use that until you're done.

You're getting this inspected, right? If your "electrician is doing it after hours / on the weekend" they still have to pull a permit. If this work causes a fire and there was no permit or inspection your homeowner's policy may deny the claim.

You are correct about it not being safe to use the outlet. However, you are wrong on the insurance issue. There is no exclusion in the Homeowners Policy for lack of a permit.

 

[DarkMatter]

Neat. I'd been told as such by an electrician. I'll check my policy documents, but I'm glad to be wrong there.

 

[Canuck]

There is no exclusion in the Homeowners Policy for lack of a permit.

There could be. More info here:

FAQ: Home Tesla charging infrastructure Q&A

The UMC can only put out 40 amps, and your car can only draw 40 amps max using the UMC so you are fine. You only need to dial down the amps if the connection is undersized. You are oversized so there's no concern.

I take this back. I'm not an electrician and others here know more than me on this issue. Always best to err on the side of caution.

 

[mspohr]

It's not a stupid question, it's a stupid and dangerous installation. The 14-50 outlet needs to be on a 50A breaker. Otherwise why even bother with a breaker at all?

I'm not an electrician but I don't see a problem here.
My house has lots of 15 amp sockets connected to 12 ga (20 amp) wires and breakers. This meets code (just went through a building project and lots of inspections). The breaker is sized for the wire to prevent the wire overheating and burning the house down, not the socket at the end. In this case, the wire is oversize so no problem. The socket itself is designated to carry a max of 50 amps and anything that plugs into it (such as the UMC) shouldn't draw more than 50 amps.
Ha! Just found this:
For circuits greater than 20 amps: A single receptacle must have an ampere rating of not less than the overcurrent device protecting the branch circuit [210.21(B)(1)]
Looks like you'd be OK to code if you had a 50 breaker on that circuit.
Practically, since we know you'll be using the UMC at 40 amps max, you should be fine for a week until the electrician comes back.

 

[DarkMatter]

I'm not an electrician but I don't see a problem here.
My house has lots of 15 amp sockets connected to 12 ga (20 amp) wires and breakers. This meets code (just went through a building project and lots of inspections). The breaker is sized for the wire to prevent the wire overheating and burning the house down, not the socket at the end. In this case, the wire is oversize so no problem. The socket itself is designated to carry a max of 50 amps and anything that plugs into it (such as the UMC) shouldn't draw more than 50 amps.

A single receptacle installed on an individual branch circuit must have an ampere rating equal to the rating of that circuit. [210-21(b)(1)] An individual branch circuit supplies only one piece of utilization equipment. A single receptacle installed on a 15-ampere branch circuit must have a rating of 15 amperes, while one installed on a 20-ampere branch circuit must have a rating of 20 amperes.

Your 15 ampere receptacles are allowed on a branch circuit because there are at least two. So this installation is not to code.

 

[mspohr]

A single receptacle installed on an individual branch circuit must have an ampere rating equal to the rating of that circuit. [210-21(b)(1)] An individual branch circuit supplies only one piece of utilization equipment. A single receptacle installed on a 15-ampere branch circuit must have a rating of 15 amperes, while one installed on a 20-ampere branch circuit must have a rating of 20 amperes.

Your 15 ampere receptacles are allowed on a branch circuit because there are at least two. So this installation is not to code.

This only applies to 20 amp circuits. If the circuit is more than 20 amps, the socket must be sized to the breaker. (I edited my response above).

 

[DarkMatter]

This only applies to 20 amp circuits. If the circuit is more than 20 amps, the socket must be sized to the breaker. (I edited my response above).

I think you and I said roughly the same thing, since we quoted the same code section. We just went at it in different ways. Look further down the same page and you'll see the table for outlet sizing - they don't always have to match on circuits below 50 amps. Above 50 amps they must always match the circuit size.