Tesla Listed electrician using NM-B 6/2 and configures 48A of Max charging current

[skuk]

Tesla Listed electrician using NM-B 6/2 and configures 48A of Max charging current
Tesla lists set of electrician in their site. I am more of a DIYer with EE back ground. I was getting quotes to get an idea on the cost from these listed electicians in my area. One popular electrician has done several homes in my area and this is what he does

1. Use NM-B 6/2
2. Run conduit from Main panel to point where it reached attic. In attic NM-B runs without conduit
3. Uses breaker 60A.
4. Configures charger at 48A
5. When i asked this the below he said they installed for 3000 homes and they know what they are doing and gets in to defensive conversation. Whole conversation here. I am belive there might not be issues as NEC has some buffer but its not code.

Comments ?

"If you're using 6ga THHN. wire in conduit, you're fine at 60A, but for Romex the limit is lower at 55A. Since 55A breakers are non-standard, I believe that the NEC technically allows you to upsize the breaker to 60A but that doesn't lift the actual ampacity limits of the circuit which are still dictated by the Romex at 55A peak and 44A continuous, not 48A. But the EVSE doesn't allow you to configure it for a 55A circuit, only 50A or 60A, so you have to use the lower setting of 50A anyways. But setting it to 60A peak and 48A of continuous draw is code violation and might cause some trouble down the road. Pls clarify"

 

[rwiegand]

That's exactly what my Tesla listed electrician did. Permitted, inspected, and working fine. The 6-2w/g cable doesn't warm up noticeably during charging at 48A.

 

[ucmndd]

He’s not wrong that you’re extremely unlikely to have any sort of issue.

But it’s definitely not code compliant by the letter of the law, even if lots of AHJ’s don’t catch it or don’t care.

 

[Rocky_H]

@skuk Wow! You are correct, and that so-called "electrician" is wrong and an idiot. That is definitely a code violation for exactly the reason you laid out. Setting it to run at 48A continuous means that it needs the circuit rating to be 125% of that continuous current level, which is a FULL 60A. NM-B 6 gauge only has a 55A rating limit, so it CANNOT be used on a full 60A circuit rating. Period.

He said, "We always pass inspection", but I have heard way too many stories of inspectors who barely do a drive-by and don't look at what's done, just trusting that a big name electrician company will be getting a small job correct. If you go ask some city or county inspectors if NM-B 6 gauge can be used for 60A circuit, you might get the straight-up answer that it's a code violation to show to that guy.

 

[Rocky_H]

And yes, there is the other rabbit trail you mentioned, where this could be allowed as a 55A rated circuit with 44A continuous current, but the wall connector doesn't have a setting for that. You have to choose 50A or 60A circuit, and the 60A one doesn't pass code.

 

[EVer Hopeful]

I'll say it again, but why charge at 48A?

Unless you're continually driving the thing, you'll probably come home at night, plug it in, then get something to eat, watch a bit of tele, nod off, get woken up by the misses then pad off to bed.

About an hour after you fall asleep, the car will be "full" again whatever that means, but . . .

. . . if you'd set it for 30A it would take say an extra two or even three hours - and you'd STILL be asleep!


Moral of the story: set it to charge at 30A, keep the wiring and put a 40A breaker in there. It'll be better all round with less stress etc


Badges are ok, up to a point, but having a badge doesn't mean someone is 100% reliable. Just think of where you work and some of the mutants who work with you . . .

 

[Rocky_H]

I'll say it again, but why charge at 48A?

That's not relevant though. It's more a factor of what the customer paid for versus what they got. If they paid for a 60A circuit in the job spec, they did not get that. If they would have been OK with a 50A circuit, then the fee should have been lower. Instead, it sounds like a 60A circuit was paid for, but a 50A circuit is what was actually installed.

 

[qdeathstar]

It is a code violation. I wouldn’t accept it personally. It is the electricians job to know the code. Doesn't matter if it works. There is a lot of shady *sugar* that works.

Issue is electricians from the time they are wi little aprentences are thought 14 awg is 15 amps, 12 awg is 20 amps, 10 awg is 30 amps, 8 amps is 50 amps, 6 awg is 60 amps, 4 awg is 100 amps.


They aren’t taught the eccentricities or fine details of the code, and so they learn what they are taught, even the inspectors.

 

[WindPower]

I always run 6 gauge THHN in conduit unless I need to run inside a wall. I find it’s easier to work with THHN on longer runs then NMB when you need to have cable in conduit (like when you need to run on an exterior wall).

Why don’t you ask the electrician to run THHN in conduit all the way through? Since he’s already running in conduit from the basement to the attic, it shouldn’t be too much more work to run a conduit in an attic on an exposed wall.

While I agree with the electrician that 6 gauge NMB should be fine for 48amps, even though code says it’s only good to 44 amps (just my opinion), the one hesitation in the attic is elevated temperatures in the summer. NMB is rated to around 140 degrees F while THHN is rated to around 190F. I don’t know about you, but my attic gets very hot in the summer.

 

[sleepydoc]

The reason they've 'never had a problem' is because the NEC has a buffer built in to its guidelines. 14g wire is specified for 15 amp circuits. Does that mean if you go to 16A or even 20A it will instantly explode? No, but it will run hotter, the insulation may soften and there's an increased risk of failure. The NEC isn't designed to be safe most of the time it's designed to be safe ALL of the time. 'it's worked for us before' isn't an excuse. There are smarter people looking at more data writing the code.

 

[Dennisis]

Recently I decided to swap out my 14-50 outlet for the Wall Connector - our utility will fully cover the cost of buying it so why not? Planning receipt on Tuesday I've been doing a lot of reading here and I haven't specifically seen my question addressed. As my Wall Connector will be directly behind my service panel, literally through the back of the panel and currently wired with #6/3 Romex directly through the wall, is there any provision in the code to allow for such a short run and charge at 48A? As in, if I put in a 60A breaker it would be OK to charge at 48A? As previously suggested I plan to charge at 40A max anyway but this is one scenario I hadn't seen asked/discussed. Thanks in advance!

 

[denverag03]

40 amps is the right answer. Just set it there and don’t worry about the mostly irrelevant 8 amps you are missing out on.

 

[Rocky_H]

#6/3 Romex directly through the wall, is there any provision in the code to allow for such a short run and charge at 48A? As in, if I put in a 60A breaker it would be OK to charge at 48A?

No. I would recommend reading this thread you are posting in.

Tesla Listed electrician using NM-B 6/2 and configures 48A of Max charging current

Tesla Listed electrician using NM-B 6/2 and configures 48A of Max charging current Tesla lists set of electrician in their site. I am more of a DIYer with EE back ground. I was getting quotes to get an idea on the cost from these listed electicians in my area. One popular electrician has done...

teslamotorsclub.com

That's what all of the last several comments have been specifically explaining. #6 Romex is NEVER allowed to be used for EV charging at 48A.

 

[Silicon Desert]

@skuk Wow! You are correct, and that so-called "electrician" is wrong and an idiot. That is definitely a code violation for exactly the reason you laid out. Setting it to run at 48A continuous means that it needs the circuit rating to be 125% of that continuous current level, which is a FULL 60A. NM-B 6 gauge only has a 55A rating limit, so it CANNOT be used on a full 60A circuit rating. Period.

He said, "We always pass inspection", but I have heard way too many stories of inspectors who barely do a drive-by and don't look at what's done, just trusting that a big name electrician company will be getting a small job correct. If you go ask some city or county inspectors if NM-B 6 gauge can be used for 60A circuit, you might get the straight-up answer that it's a code violation to show to that guy.

Amen to all that Mr. Rocky. Nice post.
As a side note, I will add that in my area, there is a "Tesla Recommended" electrician that wasn't even vetted by Tesla and known to be both expensive and not as thorough as other electricians. So for the OP, just to say that just because an electrician is listed by Tesla, it doesn't mean they are going to do the job right or necessarily know any more about the chargers than another electrician. When I had mine installed, I used a local guy with a high customer rating that knew a WHOLE LOT more about installing the charger than one of the other so-called Tesla listed electricians. Bottom line to me is that being listed in Tesla doesn't necessarily mean anything.

 

[Dennisis]

No. I would recommend reading this thread you are posting in.

Tesla Listed electrician using NM-B 6/2 and configures 48A of Max charging current

Tesla Listed electrician using NM-B 6/2 and configures 48A of Max charging current Tesla lists set of electrician in their site. I am more of a DIYer with EE back ground. I was getting quotes to get an idea on the cost from these listed electicians in my area. One popular electrician has done...

teslamotorsclub.com

That's what all of the last several comments have been specifically explaining. #6 Romex is NEVER allowed to be used for EV charging at 48A.

Thanks, I expected as much and plan to set it at 40A anyway to be safe but it occurred to me there might be some sort of allowance for such a short run. It's only sheathed for maybe 8" through wall so I would think heat buildup would be minimal.

 

[Rocky_H]

Thanks, I expected as much and plan to set it at 40A anyway to be safe but it occurred to me there might be some sort of allowance for such a short run. It's only sheathed for maybe 8" through wall so I would think heat buildup would be minimal.

Well, no, these are absolute minimum ratings, so you have to meet them. I get what you're thinking in principle, though, and that applies more on opposite situations. When a circuit involves a really long distance, it may have more voltage drop than people want, so that may drive the decision to use a wire gauge that is thicker than the minimum requirement.

 

[EVer Hopeful]

Fair point

As my Wall Connector will be directly behind my service panel, literally through the back of the panel and currently wired with #6/3 Romex directly through the wall, is there any provision in the code to allow for such a short run and charge at 48A? As in, if I put in a 60A breaker it would be OK to charge at 48A? As previously suggested I plan to charge at 40A max anyway but this is one scenario I hadn't seen asked/discussed. Thanks in advance!

How much difference would the extra 8A make anyway? If you're charging overnight, are you going to get up at 2am to do anything with the car?

 

[roblab]

Amen to all that Mr. Rocky. Nice post.
As a side note, I will add that in my area, there is a "Tesla Recommended" electrician that wasn't even vetted by Tesla and known to be both expensive and not as thorough as other electricians. So for the OP, just to say that just because an electrician is listed by Tesla, it doesn't mean they are going to do the job right or necessarily know any more about the chargers than another electrician. When I had mine installed, I used a local guy with a high customer rating that knew a WHOLE LOT more about installing the charger than one of the other so-called Tesla listed electricians. Bottom line to me is that being listed in Tesla doesn't necessarily mean anything.

And often, a professional has to PAY to be listed by a company. Many professionals won't do that and rely on reputation.

 

[Dennisis]

Fair point


How much difference would the extra 8A make anyway? If you're charging overnight, are you going to get up at 2am to do anything with the car?

None of course it was more an exercise in clarity. I’m looking at 8 inches through an open wall and thinking “overheat really?” This isn’t some 100 foot run through a hot attic so maybe there’s a footnote or something for extreme (short or long) runs and I hadn’t seen where anyone asked that specific question. But I’m good now, just putting it out there as maybe I’m not the only one wondering….