Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register

14-50 on 100 amp breaker? Ok to use?

This site may earn commission on affiliate links.
The easiest way to think about it is that the breaker must match the smallest amperage of the wiring or receptacle, so that all parts of the circuit are protected.

A setup that may be moderately common and allowed is:

Receptacle: 50A
Wiring: 40A
Breaker: 40A

This is allowed, because the breaker matches the smaller amperage (of the wiring). It may be done because there are no NEMA 14-40 or 6-40 receptacles or plugs. A 32A EVSE may be plugged into such an outlet.
Yes, while this may be "allowed" I would say it is not "recommended". If this is done I would put a label on the outlet that says "32 AMPS MAX DRAW" or something like that. A person could easily assume the wiring is rated for 50 amps bc it is a 14-50 receptacle, which is a pretty reasonable assumption in my estimation. He/she could then simply swap the breaker for a 50 amp breaker and now you have a problem. It is "fine" if you know what you are doing and what you are using it for, but it could cause problems for a future person down the road. That is why I always say wire the circuit for the max rated output bc you never know what someone may be doing down the road or you may even forget yourself. This is also a very specific EV charging case as Tesla has limited the mobile connector to 32 amps instead of 40 amps like the old corded mobile connector allows for. I don't think anyone is using a 14-50 outlet and then limiting it to 32 amps only in a normal use case.
 
I don't think anyone is using a 14-50 outlet and then limiting it to 32 amps only in a normal use case.
Actually, using a 40a breaker and wiring with a 14-50/6-50 is a very common install method for normal J1772 EVSEs as almost all of them are 30 or 32a max. I think it also gets used a lot with welders and power tool installations. As I recall, the prevalance of this kind of setup was one of the reasons given for changing the old 14-50 UMC adapters from 40a to 32a.
 
He/she could then simply swap the breaker for a 50 amp breaker and now you have a problem.
Nothing stops anyone from putting a 100A breaker on any circuit in their house. This is like saying we should put 6 gauge wires everywhere in a house in case someone slaps a 100A breaker in.

Remember that normal wiring in a house is TONS of 15A outlets on a single 15A breaker. Even normal wall outlets are two 15A outlets right on top of one another even though you can only use 15A total. People pop breakers all the time in houses because breakers protect wires, not outlets. Nobody says "but what if someone throws a different breaker in!?"

My garage has 4 50A outlets on one 50A breaker and 50A wiring. Yep, I can't use them all at once. Anyone that replaces a breaker without checking the wire gauge is at fault, not the original installer.
 
  • Disagree
Reactions: Jeremy3292
Nothing stops anyone from putting a 100A breaker on any circuit in their house. This is like saying we should put 6 gauge wires everywhere in a house in case someone slaps a 100A breaker in.

Remember that normal wiring in a house is TONS of 15A outlets on a single 15A breaker. Even normal wall outlets are two 15A outlets right on top of one another even though you can only use 15A total. People pop breakers all the time in houses because breakers protect wires, not outlets. Nobody says "but what if someone throws a different breaker in!?"

My garage has 4 50A outlets on one 50A breaker and 50A wiring. Yep, I can't use them all at once. Anyone that replaces a breaker without checking the wire gauge is at fault, not the original installer.
I think you are missing the forest for the trees. You are also quoting one small piece of what I said out of context and then grandstanding on that out of context statement.

It is a very reasonable conclusion that a 14-50 outlet would have 50 amp wiring, as the outlet is rated for 50 amps. Just like it is very reasonable to assume a 15 amp outlet has 15 amp wiring. It is not reasonable to conclude a 14-50 outlet would have 100 amp wiring or that a 15 amp outlet would have 30 amp wiring. You cannot idiot proof everything, sure I agree, but that's not what I was saying. Did I say do not install a 14-50 receptacle with 40 amp wiring and a 40 amp breaker? No, I did not say that. We are talking about best practices here and what is safest and what makes the most sense.
 
  • Like
Reactions: mcirish
Remember that normal wiring in a house is TONS of 15A outlets on a single 15A breaker. Even normal wall outlets are two 15A outlets right on top of one another even though you can only use 15A total. People pop breakers all the time in houses because breakers protect wires, not outlets.
The 15A breaker prevents more than 15A from going through the circuit, so that neither any part of the wiring nor any one outlet will see more than 15A.

There is no reason that this will be unsafe, although it can be inconvenient if someone plugs in more than 15A into the circuit (e.g. two 12A devices in different outlets on the circuit) and causes the breaker to open.

Nobody says "but what if someone throws a different breaker in!?"
It used to be more of a problem with screw in fuses where all of the fuses had the same screw threads, so that it was easily possible to put a larger amperage fuse where there should be a smaller one (e.g. putting in a 20A fuse where there should be a 15A fuse on a 15A circuit). Older buildings may still have such fuses. If your house is such a building, check that the correct fuses (or screw in breakers) are in place.
idcplg
 
  • Like
Reactions: Jeremy3292
You are also quoting one small piece of what I said out of context and then grandstanding on that out of context statement.
I'm not. This is what you said:
A person could easily assume the wiring is rated for 50 amps bc it is a 14-50 receptacle, which is a pretty reasonable assumption in my estimation. He/she could then simply swap the breaker for a 50 amp breaker and now you have a problem. It is "fine" if you know what you are doing and what you are using it for, but it could cause problems for a future person down the road. That is why I always say wire the circuit for the max rated output bc you never know what someone may be doing down the road or you may even forget yourself.
100% of that is based on someone changing a breaker based on "assumptions." Literally going in and unhooking a wire from a breaker, not looking at that wire gauge, and putting a bigger breaker in. None of this is based on memory, the wire gauge is printed right on the wire. Totally illegal and stupid. If we're going to protect against that, why not keep going? I mean, the old Tesla Wall Connector is rated for 100A, so they must all be wired to 100A, right? Weird that there's a 40A breaker here, let's just swap that out....

Meanwhile, undersized breakers for outlets are totally legal. You can make up "best practices" all you want, but actual required practice is to check the wire gauge and all outlets on the circuit before you arbitrarily change breaker sizes because you feel like it or are forgetful.

There is no reason that this will be unsafe, although it can be inconvenient if someone plugs in more than 15A into the circuit (e.g. two 12A devices in different outlets on the circuit) and causes the breaker to open.
You mean EXACTLY like a 40A breaker on a 50A outlet like is being discussed here?

It used to be more of a problem with screw in fuses where all of the fuses had the same screw threads,
Ok, but we are discussing a brand new install of a 240V EVSE outlet in 2022, where fuses are not allowed. (They are deadly on household 240V as only one will blow and leave the circuit half hot). It's hard to even get insurance for a home with fuses anymore. So what is the point of bringing up the risk?
 
Last edited:
Oh, and here's CA's code on EVSE installs, which specifically says:
Overcurrent Protection: To meet the loads associated with Level 2 charging, a minimum 40 amp, two-pole circuit breaker at the beginning of the circuit located in the meter-panel breaker section will be necessary if no additional loads are on the circuit.
Nothing about the outlet to be used... Just 40A minimum.
 
100% of that is based on someone changing a breaker based on "assumptions." Literally going in and unhooking a wire from a breaker, not looking at that wire gauge, and putting a bigger breaker in. None of this is based on memory, the wire gauge is printed right on the wire. Totally illegal and stupid. If we're going to protect against that, why not keep going? I mean, the old Tesla Wall Connector is rated for 100A, so they must all be wired to 100A, right? Weird that there's a 40A breaker here, let's just swap that out....

Meanwhile, undersized breakers for outlets are totally legal. You can make up "best practices" all you want, but actual required practice is to check the wire gauge and all outlets on the circuit before you arbitrarily change breaker sizes because you feel like it or are forgetful.
Let's try this again since you apparently like selective reading. Here is my entire post below:

"Yes, while this may be "allowed" I would say it is not "recommended". If this is done I would put a label on the outlet that says "32 AMPS MAX DRAW" or something like that. A person could easily assume the wiring is rated for 50 amps bc it is a 14-50 receptacle, which is a pretty reasonable assumption in my estimation. He/she could then simply swap the breaker for a 50 amp breaker and now you have a problem. It is "fine" if you know what you are doing and what you are using it for, but it could cause problems for a future person down the road. That is why I always say wire the circuit for the max rated output bc you never know what someone may be doing down the road or you may even forget yourself. This is also a very specific EV charging case as Tesla has limited the mobile connector to 32 amps instead of 40 amps like the old corded mobile connector allows for. I don't think anyone is using a 14-50 outlet and then limiting it to 32 amps only in a normal use case."

Please let me know where I said do NOT install a 40 amp breaker and 40 amp wire on a 14-50 receptacle?
Please let me know where said that wasn't legal?
Please let me know where I said you shouldn't bother checking the wire if you are swapping the breaker?

Again just read what I wrote and not what you think I wrote and not infer things that I didn't say...
 
Coming back to the original question on this forum :D

Question: "14-50 on 100 amp breaker? Ok to use?"
Answer: "No! It is not OK to use. The 14-50 outlet is rated for 50A! Use it with a 50A breaker!"

I am playing again my "I am an Electrical Engineer" card. This should be end of this discussion or I will seriously return/destroy my diploma since there are so many "experts" out there who seem to know better :D
 
Please let me know where I said do NOT install a 40 amp breaker and 40 amp wire on a 14-50 receptacle?
Please let me know where I said you shouldn't bother checking the wire if you are swapping the breaker?

A person could easily assume the wiring is rated for 50 amps bc it is a 14-50 receptacle, which is a pretty reasonable assumption in my estimation. He/she could then simply swap the breaker for a 50 amp breaker and now you have a problem. ... That is why I always say wire the circuit for the max rated output bc you never know what someone may be doing down the road or you may even forget yourself.
Plus this:
1655244105791.png

Right below this:
Anyone that replaces a breaker without checking the wire gauge is at fault, not the original installer.
 
Last edited:
  • Disagree
Reactions: Jeremy3292
Plus this:
View attachment 816648
Right below this:
As usual, you are taking my comments out of context. My words were as follows:

"It is "fine" if you know what you are doing and what you are using it for, but it could cause problems for a future person down the road. That is why I always say wire the circuit for the max rated output bc you never know what someone may be doing down the road or you may even forget yourself."

The latter sentence, which you quoted, is directly commenting on the former sentence where I said is it fine to do but since it can cause future problems, I always wire for max output. Note that I said "I would do X just to be safe" but nowhere did I say "you couldn't do Y." In fact I very explicitly said it is fine to do.

I also said it is a "reasonable assumption in my estimation" the wiring on a 50 amp outlet would be 50 amp rated. Never once did I say "don't check it" or "you should be fine as is." I simply said it is a reasonable assumption in my estimation, which it is.

This will be my last post on the topic as you appear to just enjoy arguing for no reason about something I didn't even say.

Say what you mean, mean what you say.
 
I am an EE and I strongly suggest to install the correct wire size and a 50A breaker on the circuit that you have the 14-50 NEMA outlet installed since it is rated for 50A.

I'm an EE and I'm a power engineer. As long as the wiring is appropriate, you can put a 14-50R on a 100A Circuit and Protection. The protection should be from the outlet itself where the outlet cannot take a load greater than 50A.
The easiest way to think about it is that the breaker must match the smallest amperage of the wiring or receptacle, so that all parts of the circuit are protected.

A setup that may be moderately common and allowed is:

Receptacle: 50A
Wiring: 40A
Breaker: 40A

This is allowed, because the breaker matches the smaller amperage (of the wiring). It may be done because there are no NEMA 14-40 or 6-40 receptacles or plugs. A 32A EVSE may be plugged into such an outlet.

The following is also true, and commonly installed in home circuits.
Receptacle: 15A
Wiring: 20A
Breaker: 20A

Thus:

Receptacle: 50A
Wiring: 100A
Breaker: 100A

"should be allowed"

The protection is the Receptacle itself not allowing more than 50A. It won't protect against a badly DESIGNED load, but it will protect the wiring from causing a fire. There is nothing in the NEC that states the above is not allowed. While I'm not an electrician, I looked up the NEC on the subject and I couldn't find the wording that states the above situation is not allowed. NEC Article 625.



That being said, I HIGHLY doubt a 100A wiring can fit in 14-50 receptacle, so even though you could by code and safety put a 100A breaker and a 50A Receptacle, I don't think its physically POSSIBLE to put a 50R on a 100A circuit because the wiring would be too thick to put into the terminals.
 
  • Like
Reactions: arnolddeleon
Could you explain why it was allowed and why the latter is not allowed?
Because houses often have tons of 5-15 receptacles on one circuit. It's pretty convenient to be able to actually be able to plug in a ton of 100W things without blowing the breaker just because the sum of them is higher than one outlet could handle, but no one device is anywhere near an issue. And 5-15 devices run the whole gamut from 1W to 1500W, so a mix of them can easily be under the 2400W/20A limit without a single one stressing an outlet at all. There's a risk/reward here, and it's worth it.

The burning you see won't be saved by a breaker. It looks like a liquid problem actually. But the chance that a outlet is overheating because the LOAD is greater than 15A but less than 20A is very low. You can melt a worn out 15A outlet at 5A if the heat it is generating is enough, and the breaker will never care. So part of this is that 5A of overhead isn't a lot and is a super unlikely amount to end up with when a device fails.

Meanwhile, at 50A, lots of things sized that way actually draw that. Nobody builds a 280W device with a 50A plug on it. Since there are 20, 30, and 50A plugs, devices tend to use the smallest one they can support, so unless you can double the socket rating with your wiring, it doesn't help a lot. It's kinda like "well, if you put this end on, you're probably gonna draw most of it"- so there's no point in allowing 5A or 10A of overhead, two devices with 50A plugs will just go and blow it every time. So now you need 100A on a 50A outlet. That risk isn't worth the reward. Note you ARE allowed multiple 50A sockets on one 50A circuit, which is safe because you can't overload the socket, it's just a hassle for the user if they try and run two things at once.

There's a whole table in the NEC, and you can see that they only allow this at lower amperages, and in upper ones, they specifically allow lower circuits than receptacles, but not greater.

1655252051815.png
 
Last edited:
Could you explain why it was allowed and why the latter is not allowed?
I think it's mainly because there are generally so many 5-15 receptacles on a single circuit. It makes sense to have a 20a circuit, but no actual loads greater than 15a. I also suspect that modern 5-15 receptacles are probably engineered so that 20a won't cause them to catch fire.
 
I think it's mainly because there are generally so many 5-15 receptacles on a single circuit. It makes sense to have a 20a circuit, but no actual loads greater than 15a. I also suspect that modern 5-15 receptacles are probably engineered so that 20a won't cause them to catch fire.
This suspicion is correct. UL listed 15A receptacles are actually required to handle 20A internally (passthrough), only the plug is different. The reason is as described above where commonly you use a 20A circuit with a lot of 5-15 receptacles.
Can you put 15A outlets on a 20A circuit?
This is part of the UL498 standard:
UL Standard | UL 498

Basically this whole discussion teaches a lesson, that just because an exception is allowed in one specific case doesn't mean it applies to everything.
 
I'm an EE and I'm a power engineer. As long as the wiring is appropriate, you can put a 14-50R on a 100A Circuit and Protection. The protection should be from the outlet itself where the outlet cannot take a load greater than 50A.

The original question is if the 14-50 can be used on a 100A breaker which should not be done. 14-50 on a 100A circuit with 50A breaker protection is something different but that was not asked.
 
  • Like
Reactions: Jedi2155
The protection is the Receptacle itself not allowing more than 50A. It won't protect against a badly DESIGNED load, but it will protect the wiring from causing a fire. There is nothing in the NEC that states the above is not allowed. While I'm not an electrician, I looked up the NEC on the subject and I couldn't find the wording that states the above situation is not allowed. NEC Article 625.

The other points others already addressed, but I'm not quite following this. The receptacles themselves offer no protection against using more than 50A. They are simply rated for that, but they are not designed to "fail safely" when you reach past 50A. The way they fail can lead to fire (just like it can for the wires), there is no additional fuse inside or circuit breaker. If you are "lucky" it melts in a way that disconnects the circuit or you discover the melting/heat/smoke before fire, but that doesn't necessarily happen. That's why you need a circuit breaker or fuse panel in the first place.
That being said, I HIGHLY doubt a 100A wiring can fit in 14-50 receptacle, so even though you could by code and safety put a 100A breaker and a 50A Receptacle, I don't think its physically POSSIBLE to put a 50R on a 100A circuit because the wiring would be too thick to put into the terminals.
I discussed this up thread, 100A requires at minimum 3 AWG copper according to NEC, for 60C rating it requires 1 AWG

I don't think there are 14-50 outlets designed for those wire sizes, and it would be a code violation to use wire sizes that the outlet was not designed for.

For example, Hubbell instructions require looking at 60C rating (this is mainly for saying you need to use 6 AWG instead of 8 AWG for 50A), and given 4 AWG max size, the max current rating allowed by the conductor would be 70A.
14-50 on 100 amp breaker? Ok to use?
 
Last edited:
  • Like
Reactions: Jeremy3292
Funny enough, upon further study:
"In the US you can use a 15 amp outlet (technically called a receptacle) on a 20 amp circuit, as long as there is more than one receptacle on that circuit."
This would not be allowed on on a 20A circuit by itself.
1655257858612.png

But this would be allowed:
1655257882153.png



Basically, there needs to be the potential for the circuit to be overloaded for the oversizing of the circuit to occur. More fun, is that this is not allowed in Canada, where the receptacle HAS to match the circuit rating.

The receptacles themselves offer no protection against using more than 50A. They are simply rated for that, but they are not designed to "fail safely" when you reach past 50A.
My understanding here is that at no time the load on the other end of the receptacle should be allowed to draw more than 50A, which is fundamentally a limit of the receptacle if designed correctly. I agree that it is not designed to "fail safely" which is a limitation of US code (compared to UK codes). Then again the reason we use protection is for the times when thing aren't working as expected, but in this case the failure point would remain at the receptacle, which can happen for for all sorts of reasons.