Is #8 THHN with Tesla Wall Charger Up To Code? (On 50A Breaker)

[ghsnick!]

I’m trying to get a better understanding of this installation and I believe the manual calls for #6 wire…which can be on a 60A Breaker and chargers at 48A.

But, if it’s on a 50A Breaker, charging at 40A, would #8 THHN be up to code?

https://www.tesla.com/sites/default/files/support/charging/Gen3_WallConnector_Installation_Manual.pdf

Can anyone chime in on this? Thanks

 

[ATPMSD]

I’m trying to get a bette understanding of this installation and I believe the manual calls for #6 wire…which can be on a 60A Breaker and chargers at 48A.

If we are talking about #6 Romex (NM-B) ,then no. #6 THHN will work.

But, if it’s on a 50A Breaker, charging at 40A, would #8 THHN be up to code?

If it is copper, then yes

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

 

[ghsnick!]

If we are talking about #6 Romex (NM-B) ,then no. #6 THHN will work.



If it is copper, then yes

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

I can only use a 50A breaker due to other limitations outside of my control, so I will have a 50A breaker and when I select that in the Tesla App, it only allows a max charge of 40A.

I’m using #8 THHN (Copper). Here are two pics….

Just to confirm - this is up to code and safe for it being on a 50A breaker and charging at 40A?

 

[fiehlsport]

Yes. #8 THHN in PVC, flex, or EMT conduit is appropriate for 40A continuous charging on a 50A circuit.

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

Look at the 90C column, then derate by 80% since EV charging is a continuous load, and you're still good.

 

[Sophias_dad]

I can only use a 50A breaker due to other limitations outside of my control, so I will have a 50A breaker and when I select that in the Tesla App, it only allows a max charge of 40A.

Make sure you set that 50A breaker setting IN THE HPWC, and not just select 40A in the tesla app.

The manual is just giving specs for the 60/48A charging case, and doing a pretty poor job of it at that.

 

[Cosmacelf]

Yes, 8 gauge THHN in conduit works for 50A. More info: Advice for EV Charging in North America

 

[ATPMSD]

I’m using #8 THHN (Copper). Here are two pics…

You should not use two black wires. One wire should be black and the other red. The ground wire should be either green or bare copper; #10 wire should be fine for the ground.

 

[ucmndd]

You should not use two black wires.

There’s really no issue with this. Perfectly acceptable to wrap the ends of one with some red electrical tape for easy differentiation on each end of the circuit.

 

[Cosmacelf]

You should not use two black wires. One wire should be black and the other red. The ground wire should be either green or bare copper; #10 wire should be fine for the ground.

What?? They are both hots. Two black wires on a 240V circuit is fine. Doesn’t matter which is which.

 

[ATPMSD]

There’s really no issue with this. Perfectly acceptable to wrap the ends of one with some red electrical tape for easy differentiation on each end of the circuit.

As long as you do not mix up the wires when taping of course.

 

[ATPMSD]

What?? They are both hots. Two black wires on a 240V circuit is fine. Doesn’t matter which is which.

The red and black distinction is meant to indicate different phases. Normally, if you see two blacks wires this indicates an incoming hot wire and an outbound, such as is found in typical home outlet or lighting circuits.

I do not know if the red/black is “code” but it is common practice.

 

[tga]

Yes. #8 THHN in PVC, flex, or EMT conduit is appropriate for 40A continuous charging on a 50A circuit.

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

Look at the 90C column, then derate by 80% since EV charging is a continuous load, and you're still good.

You can only use the 90C column if your wire, and the terminals it connects to, are 90C rated. I don't think the WC terminal are (only 75C), and I've never seen a residential breaker with 90C terminals. But even following the 75C column, #8 THHN @ 40A charging is fine.

 

[davewill]

There’s really no issue with this. Perfectly acceptable to wrap the ends of one with some red electrical tape for easy differentiation on each end of the circuit.

Not even that is necessary. There's no need to differentiate the two hots from each other. When my electrician ran my 14-50, he used three black wires and one green, and just marked the neutral with white at each end. I assume it was easier to have just one spool of black wire on the truck rather have three colors on board.

 

[ghsnick!]

You can only use the 90C column if your wire, and the terminals it connects to, are 90C rated. I don't think the WC terminal are (only 75C), and I've never seen a residential breaker with 90C terminals. But even following the 75C column, #8 THHN @ 40A charging is fine.

Question - I have #6 NM-B to a junction box. The connection was made there with #8 THHN.

Technically it is hardwired to the Tesla Wall Charger, but it goes like this.

50A Breaker > #6 NM-B > Junction Box > #8 THHN > Tesla Wall Charger

Does the first part of the run being #6 NM-B mess anything up with the ratings?

 

[tga]

Question - I have #6 NM-B to a junction box. The connection was made there with #8 THHN.

Technically it is hardwired to the Tesla Wall Charger, but it goes like this.

50A Breaker > #6 NM-B > Junction Box > #8 THHN > Tesla Wall Charger

Does the first part of the run being #6 NM-B mess anything up with the ratings?

I see nothing wrong with that. #6 NM-B has greater or equal ampacity (55A) at it's required 60C column than #8 at at any temp.

 

[Cosmacelf]

Question - I have #6 NM-B to a junction box. The connection was made there with #8 THHN.

Technically it is hardwired to the Tesla Wall Charger, but it goes like this.

50A Breaker > #6 NM-B > Junction Box > #8 THHN > Tesla Wall Charger

Does the first part of the run being #6 NM-B mess anything up with the ratings?

No, since you are using a 50A breaker. #6 NM-B is fully compliant with a 50A breaker. Some people try to use #6 NM-B with a 60A breaker, and that's where it isn't compliant with the NEC.

 

[Rocky_H]

50A Breaker > #6 NM-B > Junction Box > #8 THHN > Tesla Wall Charger

Does the first part of the run being #6 NM-B mess anything up with the ratings?

"mess anything up" is kind of the wrong way to look at it. They can all be fine if everything is selected properly to comply with the given limits. And whatever has the worst case limitation is what you have to use for the limitation of the whole thing. The #6 NM-B has a 55A limit. The #8 THHN in conduit has a 50A limit. So 50 is as high as it is allowed to go to comply with both wire segments.

 

[ghsnick!]

I see nothing wrong with that. #6 NM-B has greater or equal ampacity (55A) at it's required 60C column than #8 at at any temp.

No, since you are using a 50A breaker. #6 NM-B is fully compliant with a 50A breaker. Some people try to use #6 NM-B with a 60A breaker, and that's where it isn't compliant with the NEC.

"mess anything up" is kind of the wrong way to look at it. They can all be fine if everything is selected properly to comply with the given limits. And whatever has the worst case limitation is what you have to use for the limitation of the whole thing. The #6 NM-B has a 55A limit. The #8 THHN in conduit has a 50A limit. So 50 is as high as it is allowed to go to comply with both wire segments.

Thanks for all the helpful responses…glad to know I’m up to code at a 50A breaker (which charges at 40A).

Two more questions…

1. Is the #8 THHN good up to 50A or 55A? I’m honestly just curious and want to educate myself better.

2. If using #6 NM-B wire to hardwire to a Tesla Wall Charger, I know the white/neutral is capped off by itself and not used…red and black wires go to the hots on the charger. But is the single copper/ground wire enough (from a #6 NM-B) to be used as the ground? I notice that ground wire is a lot skinnier than the other wires, even within the #6 NM-B.

 

[ATPMSD]

But is the single copper/ground wire enough (from a #6 NM-B) to be used as the ground?

Yes. As to your capacity question:

Cerrowire Resources - Ampacity Charts

Ampacity is the maximum current that a conductor can carry continuously under the conditions of use without exceeding its temperature rating. Cerrowire's ampacity chart helps calculate the load requirement for a circuit.

www.cerrowire.com

 

[Cosmacelf]

Thanks for all the helpful responses…glad to know I’m up to code at a 50A breaker (which charges at 40A).

Two more questions…

1. Is the #8 THHN good up to 50A or 55A? I’m honestly just curious and want to educate myself better.

2. If using #6 NM-B wire to hardwire to a Tesla Wall Charger, I know the white/neutral is capped off by itself and not used…red and black wires go to the hots on the charger. But is the single copper/ground wire enough (from a #6 NM-B) to be used as the ground? I notice that ground wire is a lot skinnier than the other wires, even within the #6 NM-B.

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Advice for EV Charging in North America

Advice for EV Charging in North America

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