You can’t put a 15 on a 20 because it would violate code since there are 15 amp circuit breakers. There are not 55 amp circuit breakers so the code in the post you quoted specifically allows moving up to a 60 amp breaker. It is not uncommon to do so.
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Tesla wall charger users. What size wire is your charger using?
- Thread starter ozziegn
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You can’t put a 15 on a 20 because it would violate code since there are 15 amp circuit breakers. There are not 55 amp circuit breakers so the code in the post you quoted specifically allows moving up to a 60 amp breaker. It is not uncommon to do so.
I'll need chapter and verse on that one as there is absolutely no safety issue with putting a smaller load on a larger circuit as long as the breaker is sized to protect the wire.
You are right. I was typing during lunch and am not even sure what I was trying to say.
ucmndd
Well-Known Member
Pretty sure he's saying you can't use the "round up" rule to put a 20 amp breaker on a circuit with 15 amp conductors because of the wide availability of 15 amp breakers.
The current a wire can carry depends on the acceptable temperature rise, local codes, and ratings for anything the wire comes into contact with. Typically you can use the 'next size up' breaker if the specific one is not available. Alternatively you can run larger wire so long as the breaker and terminals on the load are rated for it.
Personally, i'd run #4 THHN in EMT, with a 60A breaker for a wall charger. If the house has 100A service then make it a 40A breaker with #6 or #4. You can oversize the conductor as much as youd like to meet voltage drop requirements. The terminals need to be rated for the size of the conductor of course, so there are practical limits on how far this can go. You'd likely have to step the breaker size above 60A to get larger than #4 or #2 wire into the breaker depending on the model. But you can absolutely run the Wall Connector on a 80A breaker with #1THHN and set the rotary dial to the '60A' breaker setting if you really wanted to go overboard. All conductors will have temperature rise for any non zero load. A larger conductor will have less temperature rise for the same load, but you can physically pass thousands of amps across #6 copper. Just not for long.
Personally, i'd run #4 THHN in EMT, with a 60A breaker for a wall charger. If the house has 100A service then make it a 40A breaker with #6 or #4. You can oversize the conductor as much as youd like to meet voltage drop requirements. The terminals need to be rated for the size of the conductor of course, so there are practical limits on how far this can go. You'd likely have to step the breaker size above 60A to get larger than #4 or #2 wire into the breaker depending on the model. But you can absolutely run the Wall Connector on a 80A breaker with #1THHN and set the rotary dial to the '60A' breaker setting if you really wanted to go overboard. All conductors will have temperature rise for any non zero load. A larger conductor will have less temperature rise for the same load, but you can physically pass thousands of amps across #6 copper. Just not for long.
Yep. Also, you can't run a 20A outlet on a 15A circuit since it could be misleading, even if its #12 wire. It's technically not dangerous, but its not code compliant. Same story with larger plugs unless specifically listed otherwise. You could run #4 THHN on a 5A breaker if you want, so long as the breaker is rated for that size wire.
You are saying that if I have #6 60°C rated wire I can wire that to a 60 A breaker if I can't find a 55 (which is what this wire is rated for)?
Thanks, after re-reading that is indeed what I was trying to communicate while hastily typing on my phone.
Yep. The "standard" breakers are defined by code as well. As you can see, 55 amp breakers are not "standard" by code and therefore the code section noted previously (and copied below) applies and the circuit breaker can be rounded up to 60 amps.
240.6(A) Fuses and Fixed-Trip Circuit Breakers. The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 110, 125, 150, 175, 200, 225, 250, 300, 350, 400, 450, 500, 600, 700, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000, and 6000 amperes. Additional standard ampere ratings for fuses shall be 1, 3, 6, 10, and 601. The use of fuses and inverse time circuit breakers with nonstandard ampere ratings shall be permitted.
eprosenx
Active Member
So the 15a receptacle example on a 20a circuit is actually not a fantastic example since we run into some other weird code exceptions. One is that for whatever reason in the US they let you put 15a receptacles on 20a circuits along with 20a receptacles. Normally you can not have a receptacle installed on a circuit breakered higher than the rating of the receptacle. 15a is the exception. The other weirdness is that 14awg, 12awg, and 10awg wire (actually and some smaller sizes) are prescriptive in the max breaker size. Even though 14awg copper is rated to 20 amps at 75c insulation ratings, you are not allowed to use it on a breaker greater than 15 amps. So the next size up rule never comes into play for the most part (you would have to be forced to derate the crud out of it in order for the next size up rule to come into play, and you would only be able to have a single receptacle on a specific device for that to apply).
But to answer your supposition: Very clearly the code snippet I posted 240.4(B) allows for what I describe. Basically they allow you to make use of the full ampacity of the wire even if the exact right breaker does not exist. You get to round up vs. rounding down.
So there are limits to this. You can not put a receptacle on a circuit that is rated less than the rating of the circuit. This is to keep the receptacle from melting if something goes wrong but without the breaker tripping. Also, hardwired devices will typically define what the max circuit size you are allowed to put them on. They generally rely to some degree on external overcurrent protection (AC units are a great example of this).
Actually, most 60a breakers will take a #4 AWG wire. If nothing else because they are rated to take aluminum wire which has to be bigger for the same rating.
So actually.... This is really weird, but you are allowed to have a single receptacle on a dedicated circuit that is rated higher than the circuit as long as your "load to be served" is within the capacity of the circuit. So like you could have a 6-50 receptacle on a 30a circuit if you wanted in order to power an EVSE that only drew 24a or 16a. This seems really weird and I would not generally recommend it, but as far as I can tell, it is fully allowed by the code. (I have posted about this elsewhere here)
Correct. It is your choice per the code. As long as you are not trying to land it on a receptacle only rated for 50 amps.
I generally would not recommend it unless you had a really good reason. Note that the new ChargePoint home charger is a prime reason to actually do this though. It is rated for 50a charging to the car, so it needs a circuit rated to 62.5 amps. So you can use #6 AWG copper THHN in conduit which is good to 65 amps. You then have to breaker it at 70 amps. It is a totally legit solution (and in fact, the ChargePoint only accepts wire up to 6 AWG max).
The NEC is a funny beast...
Yeah, but most won’t take #2 or #1, which is why I said larger than.
What I was getting at is there only so many options since you tend to be limited both on both ends.That’s an odd duck. I wonder if an inspector would ever allow that. I don’t see much justification for that. What if you unplug or remove the load to be served? Now it’s an improperly wired receptacle. Normally with a single outlet it needs to do what it claims. A single 5-15 needs to be on a 15A circuit, but a duplex 5-15 can be on a 20A circuit...
Sorta. It depends on the type of cable. NM cable, which is what is used to wire houses is many cases is only rated at 15 amps at 75c.. THHN is rated at 20 amps, but that is before derating... because the only way to install THHN is in conduit, you will need to derate the wire that is installed in the conduit, which reduces the maximum ampacity below the 20 amps quoted in the chart you are looking at.
naw....
210.21 Outlet Devices.
(A) Lampholders.
(B) Receptacles.
(1) Single Receptacle on an Individual Branch Circuit. A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.
(2) Total Cord-and-Plug-Connected Load. Where connected to a branch circuit supplying two or more receptacles or outlets, a receptacle shall not supply a total cord-and-plug-connected load in excess of the maximum specified in Table 210.21(B)(2).
(3) Receptacle Ratings. Where connected to a branch circuit supplying two or more receptacles or outlets, receptacle ratings shall conform to the values listed in Table 210.21(B)(3), or where larger than 50 amperes, the receptacle rating shall not be less than the branch-circuit rating.
Exception No. 1:
Exception No. 2: The ampere rating of a receptacle installed for electric discharge lighting shall be permitted to be based on 410.62(C).
(4) Range Receptacle Rating. The ampere rating of a range receptacle shall be permitted to be based on a single range demand load as specified in Table 220.55.
See my above post, NEC is very clear. You cannot put a 15 amp outlet on a 20 amp circuit. You can put multiple 15 amp outlets on a 20 amp circuit. You can put multiple 50 amp outlets on a 50 amp circuit. You cannot put a 30 amp outlet on a 50 amp circuit.
eprosenx
Active Member
Yeah, but most won’t take #2 or #1, which is why I said larger than.
My bad, I was multi-tasking when I wrote that and I misread your comment. ;-)
I don't think the inspector could deny it really. They are supposed to enforce the code as written. I think this is very clearly allowed by the code. An extremely common example is a NEMA 14-50 installed on a 40a circuit. This is exceedingly common (and in fact is totally find for UMC Gen 2). I personally don't like it or think it is a good idea, but it is a common thing and is allowed by the code. :-(
The wire ratings are the same whether NM or THHN (it is the same table in the 2017 NEC 310.15(B)(16)). It is referenced by wire size and type. What differs is what the insulation rating of the wire is and whether you are allowed to use the higher insulation ratings (NM cable is somewhat arbitrarily limited to the 60c rating in the NEC).
I am assuming you are referring to copper NM cable of 14 AWG in your comment. It is rated to 15 amps at 60c, 20 amps at 75c. So since NM cable is limited by code to the 60c rating, 15 amps is the max. THHN can also use the 75c or 90c column which is 20 and 25 amps respectively. The 90c rating is not practically usable since residential breakers and devices are generally only rated for 75c connections so that is your limiting factor. Note that all modern NM cable I am aware of and THHN cable are actually rated with 90c insulation (just you are capped by the artificial limit on NM cable to 60c and by the termination ratings to 75C for THHN). However: When you do derating for ambient temp or number of current carrying conductors in a raceway you use the 90c limit as your starting point.
Do note that THHN run in conduit does not need to be derated until you have more than three current carrying conductors in a single raceway. So to my point, 14 AWG copper in conduit is good for 20 amps as long as there are not more than three current carrying conductors in that conduit and the ambient temp is not over 86 degrees Fahrenheit.
Now, to my point, you still can't use that 14 AWG THHN in conduit on a 20 amp circuit due to those two asterisks in the table above. See 240.4(D):
Basically there are just hard limits on ampacity of these small wire gauges regardless of if the tables and deration factors would otherwise allow you to use them.
Table 210.21(B)(3) only applies to circuits with more than one receptacle on the circuit. Article 625.40 (EV Charging) actually requires that EV charging receptacles be dedicated and the only receptacle on the circuit. So we fall into 210.21(B)(1) which simply says the single receptacle on the circuit can not be rated to less than that of the branch circuit. Nothing is prescriptive here.
I think I was a bit misleading in my previous post about the 15a receptacle being allowed on a 20a circuit. I did not realize that allowance was under 210.21(B)(3), so if you only have a single receptacle on the circuit then you fall into 210.21(B)(1) and in which case you can not have a 15a receptacle on a 20a circuit. Good call out.
You can put multiple 50 amp outlets on a 50 amp circuit as long as it is not for EV charging (per Article 625.40).
And yes, +1 to your comment about not being able to put a 30a receptacle on a 50a circuit.
NO. 14 awg NM cable is only rated to 15 amps, period. How the NEC got there is irrelevant.
which means you have to derate it since most places in north america will reach 86 degrees at some point. EG an inspector isn’t going to allow you to use 14 awg wire on a 20 amp circuit in minnesota.
my point about 210.21(b)(1) was that it says you if you have a 50 amp breaker, you have to have a 50 amp or higher rate outlet,If you have a 100 amp breaker, you have to have a 100 amp or higher rated outlet. It seemed like you were arguing otherwise.
It says not less, btw.
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I would also add that an inspector (ahj) is probably not going to pass a 50 amp receptacle on a 30 amp circuit. The main reasoning behind allowing higher rated outlets on lower rated circuits is for startup stresses on motors and wasn’t really envisioned for continuous loads like ev chargers. I suspect this will be addressed in a code revision.
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SK360
Member
6/2 romex to a 60amp breaker here. Wall charger set at 40amps.
That should be a 50A breaker, not 60A. The 6 gauge romex means it has a maximum circuit rating of 55A. Now there may be some disagreement here, because some might say "next size up" on the breaker, and I guess you have the wall connector set for the lower amount, so it sets itself as if it is operating as a 50A circuit, but overall, this kind of janky mismatching stuff does not seem very good.
Either do a real 60A circuit, with real 60A rated wire, or do a real 50A circuit, with real 50A rated wire, which would be this 6 gauge romex you used.
davewill
Active Member
If they had a wall connector that could be set for a 55a circuit (44a charging), then the 60a breaker would make some sense, but otherwise it's just lowering the protection of the circuit for no purpose. Not to mention the chance that some future owner might think that this was actually a 60a circuit based on the breaker and dial up the wall connector to 48a charging erroneously.
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