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Nema 14-50 on 20A Breaker?
- Thread starter Lewisball
- Start date
ai4px
Wes
I'd love to see the section of NEC code that says this (honestly). The only exception I see for wire / breaker sizing has to do with motors due to their surge. I did look up the specs on Eaton's BR series of breakers and a BR 20amp breaker will clamp a #4-#14 wire. So I must say it seems OK to use a smaller breaker than the wiring can support... provided it can be connected safely. http://www.eaton.com/ecm/groups/public/@pub/@electrical/documents/content/vol01_tab01.pdf page 79.
All references I can find with Google about NEC refer to not /oversizing/ a breaker relative to the wiring.
If I'm missing something, cool, let me know... but I don't want to get so nit picking that we confuse folks reading this thread.
It's kind of a combination of the table in 210.24 and the table in 210.21 (b) (3).
https://www.google.com/url?sa=t&rct...ircuits.ashx&usg=AOvVaw2YT4uRHfHMEWJ-eRSlEifg
Why is it OK to use a 50 A receptacle on a 40 A circuit?
The wording of these says that the outlet type cannot be less than the circuit breaker rating. The 210.21.(b)(3) does specifically show that for 40A circuits, 40 or 50A outlets are allowed. Since there is no 40 amp outlet type, it has to go upward to the 50.
@Lewisball Regarding your situation, I also have a 125A main panel, so my situation is similar. Furnace is gas and water heater is gas, so those aren't in there, but the big electrical loads are A/C, clothes dryer, and oven. As someone mentioned, a 240V 20A circuit is fairly OK for overnight charging, so just getting a 6-20 outlet type and buying the Tesla 6-20 adapter would work pretty well for a decent charging rate.
But...30 or 40 amp might be pretty useful sometimes. Here is what I would consult with your electrician about. When doing a load calculation, there is an official provision called "non-concurrent loads". It means if two loads are not going to be used at the same time, they obviously don't BOTH need to be added to the total. You can add the bigger of the two. So in other words, if I have a 50A circuit for my oven, and want to have a 30A circuit to charge the car, I will set the car to only charge after midnight and not use the oven after midnight. So you don't need to count 50 + 30 into the load calculation. You can just use the 50, and it will be one or the other in use at a time. Or you could pick the clothes dryer versus car charging. Or you could count it the other way, with the car circuit as the bigger one--50A circuit for the car OR 30A for the dryer. You only count the 50. That would increase your house's total by 20, which he did say was acceptable.
So ask him to check the load calculation again if you consider the car charging circuit as a nighttime only load offset versus one of the big daytime only loads. You can probably get something a little bigger because it wouldn't be an entirely new amount added to the total.
But...30 or 40 amp might be pretty useful sometimes. Here is what I would consult with your electrician about. When doing a load calculation, there is an official provision called "non-concurrent loads". It means if two loads are not going to be used at the same time, they obviously don't BOTH need to be added to the total. You can add the bigger of the two. So in other words, if I have a 50A circuit for my oven, and want to have a 30A circuit to charge the car, I will set the car to only charge after midnight and not use the oven after midnight. So you don't need to count 50 + 30 into the load calculation. You can just use the 50, and it will be one or the other in use at a time. Or you could pick the clothes dryer versus car charging. Or you could count it the other way, with the car circuit as the bigger one--50A circuit for the car OR 30A for the dryer. You only count the 50. That would increase your house's total by 20, which he did say was acceptable.
So ask him to check the load calculation again if you consider the car charging circuit as a nighttime only load offset versus one of the big daytime only loads. You can probably get something a little bigger because it wouldn't be an entirely new amount added to the total.
gavine
Petrol Head turned EV Enthusiast
The other thing to consider when putting a 50A outlet on a 40A breaker is that charging a car is a sustained load for hours at a time and this is more likely to eventually trip the breaker than most appliances that typically won't be drawing the full amperage for sustained periods.
ai4px
Wes
Thanks for the link.... shaking my head.... you can use a 15 amp outlet on a 20 amp branch and you can use a 40 amp outlet on a 50 amp branch... wow. Goes against everything I know electrical..... :-/
I don't see the problem with a 15 amp outlet on a 20 amp branch. You might have 4 or 5 outlets on that circuit so it makes sense to me to have a higher amperage circuit. The important thing is to use 12ga wire on that 20 amp circuit and not 14ga like you could on a 15 amp circuit.
There are no 40 amp outlets, so your second example is moot. The common example from this thread is using a 32A EVSE on a 50 amp NEMA 6-50 outlet and a 40 amp breaker. That is actually how the installation manuals for those EVSE are written. Personally, I would use 6ga wire so that the circuit could be upgraded to 50 amps with ample wire headroom.
ai4px
Wes
How are you going to melt your 15 amp outlet with a 15 amp device? 20 amp outlets are mechanically different with one prong perpendicular.
No, that is specifically not allowed. See what it said above. The outlet type has to be at least as high as the circuit rating. So your example of a 40 amp outlet on a 50 amp branch circuit is forbidden. The example in the tables is the other way around, where it's a 40 amp branch circuit, but the outlet is 50. So think it through, the breaker will trip sooner, which is what you want with the wires being smaller.
Thanks. Sounds like we have a very similar setup. Was starting to think the same, in fact I caved in and bought a wall connector today. Only thing I need to work out now is if I need this controller, I don’t want to spend $1300 for no reason. Is there a way to set the model 3 to only charge during certain hours?
Yes, scheduled charging is now available in the Model 3 software. My car was delivered with 2018.14.13 and I have been having the car start charging at 3am on the days that I charge it.
gilscales
Banned
I have had 2 inspectors in 2 counties (Los Angeles and Orange counties) tell me that a 14-50 needs a 50A breaker UNLESS it is something that is fixed in place (like a Range) or is hardwired, I have installed at least 12 of these and the first one was on 8/3 with a 40A breaker, I was forced to change it out to a 14-30 with a 30A breaker for it to pass inspection, this was an inspector for Long Beach in LA county, I asked the next inspector in Los Alamitos, Orange county and he gave me the same info, this is just my experience but both inspectors had the same interpretation of the code.
I'd also suggest the 6-20 outlet. Since you only drive about 30km /day, that means that you will complete charging in 2 hours. Also, you want to look at not so much how long it takes to charge from 0-100, but rather, how much charge you can get overnight. So lets say you sleep only 8 hours, that makes 120 miles range on 6-20. Really, though, if you arrive home at 8pm and leave at 7am, that is 11hrs or 165 miles range. At that point, you probably will be visiting a supercharger anyways, and you can spread the charge over multiple days if you drive 200miles.
Also, why quote you 1.2k for the charge controller rather than upgrading your electrical service? Seems like 100% a waste, as in both cases you have maxed out the service to your home and if "anything" happens your next charge will be the service upgrade. If you want to take advantage of gov. offers, get your service upgraded.
What happens when you get a 2nd electric car (possible?) or want to add a new outlet somewhere?
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There are two parts to this:
(1) Yes, I think the wording in the code for this does give an example of a range, and I think it may mention "fixed in place". Some inspectors take that fixed part a little more loosely. A range usually isn't "fixed in place", and the frequent application to EVSEs are wall units that do hang with a mounting bracket, so that would usually qualify as fixed, but if you are showing that it's for a 30-some amp EVSE, they will sometimes allow that.
(2) What the heck? Are you sure you heard this right from two inspectors?
That doesn't even make any sense. If it is hardwired, then by definition it is not a device that plugs into a receptacle, so a 14-50 outlet wouldn't even be in the discussion.
My Leviton EVSE housing completely covers the plug and outlet when mounted on the wall. I would imagine that this situation would be allowed if it was a 32A unit with a 40A breaker. It is very common for plug-in EVSE with 32A delivery to the car to require a 40A breaker and use a NEMA 6-50 plug. I would imagine that most inspectors presented with an EVSE fixed to the wall with these specifications would allow it. On the other hand, a NEMA 14-50 on a 40A breaker for a portable EVSE like the Tesla Mobile connector could be reasonably denied due to the likelihood of something else being plugged into that outlet.
gilscales
Banned
My whole quote was this.
"I have had 2 inspectors in 2 counties (Los Angeles and Orange counties) tell me that a 14-50 needs a 50A breaker UNLESS it is something that is fixed in place (like a Range) or is hardwired"
Yes, I am not making this up, 2 different inspectors in 2 different counties, when I said "hardwired" I was referring to a device like an HPWC or something else that is hardwired and not a 14-50 so pardon my lack of clarity, that was my fault.
I am not saying you are wrong in your interpretation of the code as I have had more than one inspector ask for something that is not needed to meet code but when they ask I find it easier to comply! it could be that is was the way these inspectors were reading the code, odd that it was 2 of them though if so.
It depends on what kind of wire and conduit you used between the outlet and the breaker box. If you left Romex exposed, it won't pass. If you used 6ga THHN in metal conduit, it will pass. Got a picture?
ucmndd
Well-Known Member
Assuming your wire is copper, and the “4 blade” outlet you’re referring to is a NEMA 14-50, you’ve sized the conductors and breaker correctly, yes.
But as @miimura suggested, “passing inspection” will depend on a number of other factors such as how the wire was run, terminated, etc.
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