Requested 60 amp wall charger install, builder wired 6/3 NM-B. Options?

[runthejoules]

Trying to get my options without burning my new house down upon move in. I requested the builder put in wiring capable of 60 amps to allow for 48 amp max charging for a hard wire HPWC install later. I may have drives where I come home to near 5% that I would like the flexibility of the extra amperage to make another quick stop within a few hours.

The builder's contractor however installed NM-B 6/3 w/ ground wire, which I've found out is only rated for 55 amps and definitely not the continuous pull. I didn't mind the 6/3 as I understand with the neutral could remove the HPWC and install a 14-50 NEMA outlet later and change the breaker to 50A for other EVs down the line.

What options do I have if I want 48 amps and maintain ability to convert to a 14-50 or 6-50 down the line?

Would the best option is to ask for direct replacement with 4/3 wire?
The other option would be to run #6 THHN/THWN +/- neutral if I wanted ability to convert back to 14-50 down the line correct? Would I need conduit for the #6 if installed behind the sheetrock?

The sheet rock isn't up so the timing is right to make the correct change all behind the walls. The run is only about 15 feet from the breaker.

Any help would be appreciated, I've spent the afternoon trying to find the answer myself and I wasn't able to.

 

[Sophias_dad]

Just have him change it to 4-3 NMB. He might have been allowed to put in the 60 amp breaker due to the round-up rule, but if he KNOWS the circuit was for an EV, he should have upsized the wire.

BTW, a 14-50 or 6-50 wouldn't require any wiring change(aside from the outlet and breaker), it would just be limited to 40 amps continuous(50 x 80%)

You'd need to have conduit behind the walls to do individual conductors.

 

[ATPMSD]

What options do I have if I want 48 amps and maintain ability to convert to a 14-50 or 6-50 down the line?

If you leave the wiring as is you can set the Wall Connector to a 50-amp circuit, which will give you a charging rate of 40-amps. Just be sure a 50-amp breaker is being used.

 

[john pane]

If you don't want to run conduit in the walls you can use SE (service entrance) cable, e.g. SER 6-6-6-6 Cu, or SEU 6-6-6 Cu if you don't need the neutral. Home Depot and Lowes carry the SEU.

 

[Sophias_dad]

If you don't want to run conduit in the walls you can use SE (service entrance) cable, e.g. SER 6-6-6-6 Cu, or SEU 6-6-6 Cu if you don't need the neutral. Home Depot and Lowes carry the SEU.

I believe this is incorrect advice, because SER cable used for individual circuits is also supposed to use the 60C rating, and therefore 6 gauge copper is only rated to 55 amps.

 

[john pane]

I believe this is incorrect advice, because SER cable used for individual circuits is also supposed to use the 60C rating, and therefore 6 gauge copper is only rated to 55 amps.

• NEC 334.10(B)(4) Installation Methods for Branch Circuits and Feeders.
  (a) Interior Installations. In addition to the provisions of this article, TYPE SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 335, excluding 334.80. For type SE cable with ungrounded conductor sizes 10 AWG and smaller, where installed in thermal insulation, the ampacity shall be in accordance with 60ºC (140ºF) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final derated ampacity does not exceed that for a 60ºC (140ºF) rated conductor.

 

[Sophias_dad]

• NEC 334.10(B)(4) Installation Methods for Branch Circuits and Feeders.
  (a) Interior Installations. In addition to the provisions of this article, TYPE SE service-entrance cable used for interior wiring shall comply with the installation requirements of Part II of Article 335, excluding 334.80. For type SE cable with ungrounded conductor sizes 10 AWG and smaller, where installed in thermal insulation, the ampacity shall be in accordance with 60ºC (140ºF) conductor temperature rating. The maximum conductor temperature rating shall be permitted to be used for ampacity adjustment and correction purposes, if the final derated ampacity does not exceed that for a 60ºC (140ºF) rated conductor.

Fair enough, although in the version I have(2020) its 338.10(B)(4) with largely the same text.

 

[john pane]

Yes, sorry. The discrepancies are probably typos in the manually-transcribed text in my notes from 2017.

 

[rjpjnk]

There are so many stories like this unfortunately. As word spreads that 6 gauge Romex is not sufficient, more and more people will be prepared to avoid this situation either by putting the words in the contract or by being there during the install to observe. Keep spreading the word.

 

[SilverString]

Trying to get my options without burning my new house down upon move in.

Is there a single documented case of this happening anywhere? I have had my HPWC wired with #6 for years and it never gets even slightly warm when charging at 48A. The 60 amp breaker gets warmer than anything, but never hot, and the voltage drop is barely measurable below 1%. A lot depends on the length of the run. If your charger is 100 feet or more from the breaker box you might consider upgrading, otherwise I would go with what your electrician installed.

 

[rjpjnk]

Even though it may work absolutely fine with 6 gauge, the rules are the rules. It may be a stupid rule, or it may be a smart rule, but generally we like to believe they are there for a reason, to protect us. But 80% is such a nice even number one has to wonder where did it come from? Is it a rule of science, or a rule of thumb? Maybe someone will explain the history and basis for this derating limit. Hopefully it is based on some physics and some statistical analysis of circuit failure data, but it could also be just a an educated guess, or even superstition. It is interesting how fiercely it is defended.

Is moving to 87% as in your case going to burn the house down? I doubt it, but it is still illegal, and not code compliant. So cannot be recommended to anyone, even if it works fine.

 

[Genie]

Simplest is learn to live with 40A charging.
I did my WC install with 6awg XHHW in conduit thinking I would want to charge at 48 but I ended up just setting the car for 24A, because for me that is more than enough, and keeps voltage drop and circuit temp down.

 

[nwdiver]

This doesn't appear to be a clear cut issue...

6/3 nm-b​

Section 240-3 (b), Next Higher Overcurrent Device Rating. Where the ampacity of a conductor does not correspond with the standard ampere rating of a fuse or circuit breaker as listed in Section 240-6 (a), the next size up device (breaker or fuse) can be used.

So... if 6/3 nm-b is rated for 55A. And there is no such thing as a 55A breaker. Per code you can use a 60A breaker as long as the expected load is <55A. Which... 48A is <55A. So...

 

[ATPMSD]

This doesn't appear to be a clear cut issue...

6/3 nm-b​

Section 240-3 (b), Next Higher Overcurrent Device Rating. Where the ampacity of a conductor does not correspond with the standard ampere rating of a fuse or circuit breaker as listed in Section 240-6 (a), the next size up device (breaker or fuse) can be used.

So... if 6/3 nm-b is rated for 55A. And there is no such thing as a 55A breaker. Per code you can use a 60A breaker as long as the expected load is <55A. Which... 48A is <55A. So...

Yes but…

“It is true that the NEC allows for selecting the next higher amperage circuit breaker when there is no exact circuit breaker made, i.e. there is no 55A breaker so a 60A breaker can be used. The 80% rule would still apply when sizing the circuit for a continuous use equipment (charging a plug-in vehicle or EV is considered continuous use.) 80% of 55A is 44 amps, so drawing 48 amps while charging would not be in compliance with the 80% rule. To be in compliance with code the maximum amperage when charging would be limited to 40 amps as the Tesla Wall Connector can be configured for a 50A circuit, wiring but not a 55A circuit, wiring.”

 

[nwdiver]

Yes but…

“It is true that the NEC allows for selecting the next higher amperage circuit breaker when there is no exact circuit breaker made, i.e. there is no 55A breaker so a 60A breaker can be used. The 80% rule would still apply when sizing the circuit for a continuous use equipment (charging a plug-in vehicle or EV is considered continuous use.) 80% of 55A is 44 amps, so drawing 48 amps while charging would not be in compliance with the 80% rule. To be in compliance with code the maximum amperage when charging would be limited to 40 amps as the Tesla Wall Connector can be configured for a 50A circuit, wiring but not a 55A circuit, wiring.”

So 6/3 nm-b on a 60A breaker is fine he would just need to dial the HPWC to 44A.

 

[ATPMSD]

So 6/3 nm-b on a 60A breaker is fine he would just need to dial the HPWC to 44A.

If we are talking about a Gen 3 Wall Connector, that is not an option. You have to set it to a 60A circuit (48A charging which is not permitted) or 50A circuit (40A charging). Which kind of raises the question why bother with a 60A breaker at all?

 

[Rocky_H]

This doesn't appear to be a clear cut issue...

It is a clear cut issue and has been covered ad nauseam in many threads before.

So... if 6/3 nm-b is rated for 55A. And there is no such thing as a 55A breaker. Per code you can use a 60A breaker...

I'll cover this part first. People misunderstand the "round up" rule frequently. Hypothetically, you could put the 60A breaker on it, but then...do what with it? Did you forget about the wire? This is where people get it wrong. They think that once they attach the 60A breaker by rounding up, a fairy waves a magic wand all along the circuit and transforms every bit of it into being rated as a 60A circuit...but it's not. The wire is still limited at a rating of only 55A, so that is the lowest limit, and it's still a 55A circuit.

as long as the expected load is <55A. Which... 48A is <55A. So...

No. There is circuit rating versus continuous draw. The circuit rating for that 6 gauge NM-B is for 55A, which means it is allowed a continuous load of only 44A, not 48A. I have heard of I think only one model of EVSE that actually does contain a real 44A setting for 55A rated circuits, and is about the only way this could legitimately be done. But Tesla doesn't make one like that. You have to choose either the 40A or the 48A setting, and the 48A isn't allowed, because it's overloading the 55A rating of the cable.

 

[nwdiver]

It is a clear cut issue and has been covered ad nauseam in many threads before.

I'll cover this part first. People misunderstand the "round up" rule frequently. Hypothetically, you could put the 60A breaker on it, but then...do what with it? Did you forget about the wire? This is where people get it wrong. They think that once they attach the 60A breaker by rounding up, a fairy waves a magic wand all along the circuit and transforms every bit of it into being rated as a 60A circuit...but it's not. The wire is still limited at a rating of only 55A, so that is the lowest limit, and it's still a 55A circuit.


No. There is circuit rating versus continuous draw. The circuit rating for that 6 gauge NM-B is for 55A, which means it is allowed a continuous load of only 44A, not 48A. I have heard of I think only one model of EVSE that actually does contain a real 44A setting for 55A rated circuits, and is about the only way this could legitimately be done. But Tesla doesn't make one like that. You have to choose either the 40A or the 48A setting, and the 48A isn't allowed, because it's overloading the 55A rating of the cable.

You're right. Just seemed a bit odd to me the code would allow a 60A breaker but not 48A of continuous load....

 

[Rocky_H]

You're right. Just seemed a bit odd to me the code would allow a 60A breaker but not 48A of continuous load....

I think when you start multiplying in two or three kinds of derating factors with temperature conditions in really hot locations and such, it's possible to end up with some really weird numbers that aren't like the published spec that's on an even multiple of 5. Also, on this forum we're dealing with the simple case of a dedicated line with only one thing on it, but calculations for general circuits can have a mix of continuous and non continuous loads, which you add with some compensation factors, so you might end up with something like 86.4 amps, and there definitely isn't a breaker for that level, so it's saying you can just use a 90A. But it still is limited overall as 86.4.

 

[rjpjnk]

You're right. Just seemed a bit odd to me the code would allow a 60A breaker but not 48A of continuous load....

I agree. It is odd, and to me makes it harder to take the 80% rule seriously. But then, I don't make the rules