While 4/2 NM is the easy solution, 6 gauge THHN, as the post above indicated, is fine for a 60 amp breaker. You need to look at the 90C column of the table.
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Anyone use this Romex 6/3 cable during install?
- Thread starter Dugdale
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While 4/2 NM is the easy solution, 6 gauge THHN, as the post above indicated, is fine for a 60 amp breaker. You need to look at the 90C column of the table.
yes, but giving wrong information is wrong. You certainly can put 6-3 NM on a 60 amp breaker. You cannot draw 48a using 6-3 NM even if you put a 50 amp breaker on it. You also can’t use 60 amps from 6awg thwn even if you put it on a 60 amp breaker.
4-2 NM cable is exceedingly rare. Show me where you can buy it.
In fact, you wouldn’t use 4-2, you would most likely use se cable. Then you could just use #6 se cable....6-6-8 copper SE cable is rare too, but at least it’s not unobtanium...
2 bucks a foot versus whatever 4-2 NM is.
4-2 NM cable is exceedingly rare. Show me where you can buy it.
In fact, you wouldn’t use 4-2, you would most likely use se cable. Then you could just use #6 se cable....6-6-8 copper SE cable is rare too, but at least it’s not unobtanium...
2 bucks a foot versus whatever 4-2 NM is.
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I had mine wired with 4/3 last month. They had both 4/3 and 4/2 MN cable at a local electrical supply house. I used 4/3 just in case I needed the neutral in the future. I also had a 14--50 wired with 4/3 (in case I swap it for a HPWC later), but that's on a 50mamp breaker.
In hindsight, I would have used 4/2 for both (and used a 6-50 for the extra circuit); 4/3 was a bear to put in an existing wall.
I'm not sure why you say you can put a 6/3 NM on a 60 amp breaker, it's a 55 amp wire.
Show me where you can buy 4-2 nm. Also why buy NM when 6-6-8 seu is cheaper?
Because. the code is very clear on this. You can.
Johnny Vector
Member
qdeathstar is correct, I was wrong. If a standard (whatever that means) breaker is not available for the ampacity (I hate that word) of the wire, you can use the next larger size standard breaker as long as the circuit only feeds a single outlet.
And since it's more helpful to actually provide the code than to sit there smugly demonstrating your superior knowledge, here it is:
Article 240.2 (B) allows the use of 6/3 for a 60 amp breaker. Take a look. 55 is not a standard sized breaker
Careful about reviving old threads and putting bad information out there. A 60 amp breaker should NOT be used.
Wire size for wall charger
Posts 88 and 89 quickly get the right information out there.
@jcanoe, @Rocky_H, and @Magnetic Flux (amongst several others) have been very helpful in setting the record straight on this.
No, no, NO! And this is where we see how people keep getting this wrong over and over and over again (even electricians sometimes). Thank you, @bmil03 for linking to that other thread, but this was already discussed and corrected in this thread on the previous page!!
People have heard about that "next size up" rule, and they make this giant incorrect leap to the conclusion that a magic wand has now been waved that makes the whole thing, end to end, a full, legitimate 60A circuit. That is FALSE! It's still limited by the wire as a 55A circuit.
No, no, NO! And this is where we see how people keep getting this wrong over and over and over again (even electricians sometimes). Thank you, @bmil03 for linking to that other thread, but this was already discussed and corrected in this thread on the previous page!!
People have heard about that "next size up" rule, and they make this giant incorrect leap to the conclusion that a magic wand has now been waved that makes the whole thing, end to end, a full, legitimate 60A circuit. That is FALSE! It's still limited by the wire as a 55A circuit.
This whole time, I've been assuming that the "next size up" crowd were limiting the load to 44A or less, which it sounds like would be acceptable. Or am I missing something and that isn't reasonable for some reason?
IF a 60A breaker was to be used it would be incumbent on the person charging the car to limit the charging to 44A in car or, using the gen 3 HPWC as an example, when going through the original setup of the HPWC it would need to be set to 50A max using the interface. If there was an extended power outage and the HPWC reverted back to factory settings unbeknownst to the homeowner that could be dangerous if the in car method was not being used as a backup.
If relying on the in car limitation that leaves a lot margin for error considering everyone who could be charging needs to be aware of the limitation else risking a bad outcome. What about owners of the home in the future? It is just not worth the risk IMO.
No need to limit the charging in the vehicle... If you install the correct circuit and use the Tesla Wall Connector, or the Mobile Charger, that is. They automatically limit themselves (as per NEC) to 80% of the rated circuit. If you select 60A when initializing the Wall Connector, it will self-limit to 48A. The Mobile connector will self limit as well.
Makes sense. If using the mobile connector, you'd be safe since its peak is less than this anyway, AFAIK. I was still thinking of the old HPWC that had the power level set with dip switches.
I guess with gen 3 this is set in software. I'd really hope that it couldn't revert to a higher power setting on its own, as I can imagine that being less than safe in general. I can see the concern, though.
I agree, but the correct circuit is exactly what is being discussed here. To be clear 6/3 should be paired with no more than a 55A breaker.
But that's not what people do, for a few reasons. Most people get this wrong, set it as a full 60A circuit, and set the wall connector for a 60A setting, and it sends 48A to the car, which is wrong and dangerous.
The regular public doesn't know anything about the National Electric Code provision for constant loads, that need to be spec'ed with a circuit that is 125% of the constant current level. People aren't going to know about that; they're just going to use the wall connector however it's set up, so you can't set it so it will deliver 48A but people need to remember and promise that they will never run it higher than 44A. And then of course some friend comes over and just plugs in, and their car isn't set to remember to use 44A, and FIRE.
You just don't do stuff like that, because it's dangerous. The wire limit is 55, so you need to just do it as a standard 50A circuit, so everything is in compliance.
Agreed... or just do it right and run 6 AWG THHN wire if you plan to use a 60 amp circuit.
I bought that wire and everything else tonight to properly install my Wall Connector and my wife commented on how expensive it was. We will literally save that much in one month of not buying gas. I drive 110 miles a day for work and get 26 MPG. My electricity is really cheap $.06/KW and gas is over $3 a gallon again.
People just need to get the right stuff or pay someone to do it for them.
Midnightsun
Active Member
You have to wonder who dreams up these codes. It is very clear 55a is the rated capacity of 6/3 wire (in the US) however it is also very clear one can round up breaker size to suit if the breaker is not available in the exact size. This means one is allowed to use a 60a breaker on a 55a rated cable. Let's muddy the waters a little more. I am in Canada, we have romex NMD90 wire which in the states I must assume is NM-b wire. Our wire is rated at 65A yet in the states it is 55A? Does this mean in Canada we are all unsafe or are the states being over cautious? Add to this 3 different electricians in the same location will argue different points and disagree with each other on how to interpret the code. I guess at the end of the day if you have a signed paper from an electrician you are good to go or at least you have someone to blame if things go wrong that is. Personally I went with romex NMD90 6/3 on a 60a breaker on a self install.
My observations. When charging at 48A for extended periods the Tesla charge cord get considerably warm like a heated steering wheel on a low setting. I do not know what size cable is in there but no way is it 6 gauge more like 8 or smaller, that cable is tiny and 18' long! The feed to my wall connecter has absolutely no noticeable extra heat to it, remains at the temp of the garage so there cannot be much strain on this 6 gauge wire. Honestly I would be more worried about the Tesla side of it however I know this must be safe.
My observations. When charging at 48A for extended periods the Tesla charge cord get considerably warm like a heated steering wheel on a low setting. I do not know what size cable is in there but no way is it 6 gauge more like 8 or smaller, that cable is tiny and 18' long! The feed to my wall connecter has absolutely no noticeable extra heat to it, remains at the temp of the garage so there cannot be much strain on this 6 gauge wire. Honestly I would be more worried about the Tesla side of it however I know this must be safe.
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gavine
Petrol Head turned EV Enthusiast
Before the wire gets potentially hot enough to start a fire, wouldn't the car notice a voltage drop and automatically lower the amps? I have to think Tesla thought of this and if not, there would be a lot of fires.
I agree 100% with following the code and being safe and I would never trust voltage drop sensing vs. proper wiring, but I'm curious if anyone here knows whether the car does this or not.
I agree 100% with following the code and being safe and I would never trust voltage drop sensing vs. proper wiring, but I'm curious if anyone here knows whether the car does this or not.
Yes, that is a feature they added by software. It wasn't there through the first few years of the Model S, but was added I think sometime around 2015-ish? It checks the initial voltage and compares to voltage as it is ramping up the charging current, and if there is a sizeable drop, it does reduce current and shows a warning on that screen telling you that there is likely a problem in the circuit.
Don't assume those are the same. I was talking a bit in private messaging with an electrician who is in Canada, and NMD90 is just something different that Canada has, and it must be a little bit different in why it's allowed some different amp ratings at different temperatures.
Well, there are several options. I do want to emphasize that there is really nothing at all wrong with a 50A circuit! The cable is fine if you don't try to overload it by using as too big of a circuit. But also, THHN requires putting those in conduit, and if you're just dropping it down inside a wall, that's a huge pain to try to put conduit in there. So maybe it should go to 4/3 cable then. There are a few ways to do this right.
Johnny Vector
Member
The voltage drop the car senses is the total drop in the circuit, but what matters for fire safety is voltage drop per unit length of the wire. Since the car has no way of knowing the total length of the wire, it can't verify that the wire is properly rated for the load. 100 feet of 6AWG wire will have more voltage drop than 20 feet of 10AWG wire, but the former is fine for a 50 A circuit, while the latter is grossly undersized and will almost certainly result in a fire.
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