Tesla charging station

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jim123

Member
Location
new castle,de
New install, inside garage. Ceiling and walls are finished.Tesla recommends 90c #6.Can I use USE-2 copper for this application or would u recommend a different wire. I want to be able to fish down the walls , go in a junction box then 3/4” conduit to the charger. This is my first EV install.charger is 48 amps, 60 amp breaker.thanks
 
It doesn't really matter what they recommend but we use THHN 6 awg (60amps in 75 column because your breaker is probably only rated for 75)

but if you need to fish the wall with 6-3 romex (or 6-2) it is based off the calculated load of 48 amps, less than 55amps that the wire is rated for, and no 55amp breaker so next size up breaker 60amp is legal.

no need for use-2
 

jaggedben

Senior Member
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Northern California
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Solar and Energy Storage Installer
You can't use NM (aka Romex) because it isn't rated 90C. You might be able to use MC cable if the wires inside are marked for 90C.

Yes, the wire needs to be rated for continuous use. That is the same as your breaker being 60A for 48A charge current. Your wire needs to be rated for 60A. (6/3 romex also happens to be rated only 55A.)

Note: You have to use the 75C column in the article 310 tables to determine your wire size. But you have to use 90C rated wire because it's a manufacturer requirement in this case. Pretty much means you need a wire that is marked with '-2' at the end of the type. USE-2 is okay for that, but might have other issues, such as being prohibited inside buildings if not cross-listed as another type that's allowed.
 
I've always been under the impression that the continuous and non continuous is over current device only so the conductor is still sized normal. So yes the breaker needs to be 125% but the conductor just needs to be the the 55amp conductor with next size up rule.

There is no reason to use 90 degree column. OP was very specific that it's recommended (means nothing) breaker terminals are probably only 75 degree so your just wasting money.

where in NEC is conductor to be 125%?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I've always been under the impression that the continuous and non continuous is over current device only so the conductor is still sized normal. So yes the breaker needs to be 125% but the conductor just needs to be the the 55amp conductor with next size up rule.

There is no reason to use 90 degree column. OP was very specific that it's recommended (means nothing) breaker terminals are probably only 75 degree so your just wasting money.

where in NEC is conductor to be 125%?
210.19 (A)(1)
 

don_resqcapt19

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Staff member
Location
Illinois
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retired electrician
You can't use NM (aka Romex) because it isn't rated 90C. You might be able to use MC cable if the wires inside are marked for 90C.
...
The conductors in NM are required to be 90°C conductors and have been for 20 t0 30 years.
334.112 Insulation
The insulated power conductors shall be one of the types listed in Table 310.4(A) that are suitable for branch-circuit wiring or one that is identified for use in these cables. Conductor insulation shall be rated at 90°C (194°F).
However you are limited to using them at the 60°C ampacity. This would require the use of 4 AWG NM, because the required ampacity is 60 amps for this charger.

The conductors in MC are likewise required by 330.12(A) to be 90°C conductors, but the MC does not have the 60°C limitation that NM has and you could use 6 AWG MC for this application.
 

Coppersmith

Senior Member
Location
Tampa, FL, USA
Occupation
Electrical Contractor
The conductors in MC are likewise required by 330.12(A) to be 90°C conductors, but the MC does not have the 60°C limitation that NM has and you could use 6 AWG MC for this application.
Or use FMC and pull in some THHN.

I've installed lots of Tesla chargers in garages. I've always used conduit and THHN in both surface-mount and flush panel situations. It's okay to punch a hole in the drywall and connect to a KO on the bottom of the panel. If it's surface-mounted and they boxed the bottom in, a hole saw will solve that problem. Usually EMT, but sometimes it's as little as a rigid conduit offset nipple.
 
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don_resqcapt19

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Illinois
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retired electrician
I'm confused why 99 degree is still being brought up even when the circuit breaker will probably be 75 degree?
The OP said the recommendation from Tesla was to use 90°C wire, but they specified 6 AWG on a 60 amp breaker which is less than the 75°C ampacity of the conductor.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
However you are limited to using them at the 60°C ampacity. This would require the use of 4 AWG NM, because the required ampacity is 60 amps for this charger.
Agreed, but I see no good reason for the NEC to require a 60A ampacity for this application. An ampacity of at least 48A, and at least sufficient to be properly protected by a 60A breaker (i.e. just over 50A) should be allowed. For further discussion, see https://xenforo.mikeholt.com/threads/215-2-a-1-a-and-240-4-b-interaction.2560991/

For the OP, you could consider using type SE cable (SER or SEU). The Tesla Gen 3 Wall Connector manual specifies copper only terminations, but since you have mentioned a junction box, you could splice from Al to Cu there. As long as you aren't under the 2014 NEC and installing in thermal insulation, you can use the 75C ampacity for type SE cable.

Cheers, Wayne
 

don_resqcapt19

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Location
Illinois
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retired electrician
Agreed, but I see no good reason for the NEC to require a 60A ampacity for this application. An ampacity of at least 48A, and at least sufficient to be properly protected by a 60A breaker (i.e. just over 50A) should be allowed. For further discussion, see https://xenforo.mikeholt.com/threads/215-2-a-1-a-and-240-4-b-interaction.2560991/

For the OP, you could consider using type SE cable (SER or SEU). The Tesla Gen 3 Wall Connector manual specifies copper only terminations, but since you have mentioned a junction box, you could splice from Al to Cu there. As long as you aren't under the 2014 NEC and installing in thermal insulation, you can use the 75C ampacity for type SE cable.

Cheers, Wayne
625.41 requires the branch circuit for electrical vehicle charging to be treated as a continuous load, and when that is combined with 210.19 that requires 60 amp conductors and OCPD.
 

Frank DuVal

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Fredericksburg, VA 21 Hours from Winged Horses wi
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Electrical Contractor, Electrical Engineer
You can't use NM (aka Romex) because it isn't rated 90C.

OK, but you can not buy it new off the shelf either!

NM-B is 90° C rated. And that is what is on the supplier's shelf. ;)

I do see Southwire says it is 90° C rated, but ampacity should be from the 60° C table. How confusing is that? :LOL:

 

don_resqcapt19

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Illinois
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retired electrician
OK, but you can not buy it new off the shelf either!

NM-B is 90° C rated. And that is what is on the supplier's shelf. ;)

I do see Southwire says it is 90° C rated, but ampacity should be from the 60° C table. How confusing is that? :LOL:

That is what has been required by the NEC since at least the 1999 code. The code requires that NM be constructed with conductors rated 90°C and limits those same conductors to their 60°C ampacity. You are permitted to use the 90°C ampacity for ampacity adjustment and/or ampacity correction where required.
 

wwhitney

Senior Member
Location
Berkeley, CA
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Retired
625.41 requires the branch circuit for electrical vehicle charging to be treated as a continuous load, and when that is combined with 210.19 that requires 60 amp conductors and OCPD.
Yes, my point is that (2017) 210.19(A)(1)(a) should be deleted. 210.20(A) is sufficient, and usually it means that the requirement of 210.19(A)(1)(a) will be met. However, in a case like the OP, where it is possible to meet 210.20(A) without complying with 210.19(A)(1)(a), I don't see the point of the additional conductor upsizing required by 210.19(A)(1)(a).

Basically, what is the problem with 55A ampacity conductors for a 48A continuous load on a 60A breaker that 210.19(A)(1)(a) is trying to address?

Cheers, Wayne
 

hillbilly1

Senior Member
Location
Atlanta,Ga
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Field coordinator/ technical support
OK, but you can not buy it new off the shelf either!

NM-B is 90° C rated. And that is what is on the supplier's shelf. ;)

I do see Southwire says it is 90° C rated, but ampacity should be from the 60° C table. How confusing is that? :LOL:

I think one of the reasons they did that, is because incandescent light fixtures created a lot of heat, which before they started putting an insulation pad in them, was cooking the old 60 degree wire. Especially if the maximum wattage was exceeded. I have seen plastic ceiling boxes melted enough that the fixture fell from 100 watt light bulbs in a fixture rated for only 60 watt.
 
The OP said the recommendation from Tesla was to use 90°C wire, but they specified 6 AWG on a 60 amp breaker which is less than the 75°C ampacity of the conductor.
I guess what I'm asking is if it's only a recommendation then why do you have to do it? Most manufacturers recommend a lot of expensive and stupid stuff so my point is that you do not need 90 degree conductors to stay within legal code. It's simply recommended. However the copper conductor terminals only is a requirement.
 
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