# 50 amp plug on 30 amp circuit



## matthewsx (Apr 23, 2019)

Here's a question for the electricians out there. I have a 30 amp sub panel in my garage and want to know if it's a code violation to wire a 50 amp receptacle into it. 

TIA,

John


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## mksj (Apr 23, 2019)

Not an electrician, but from what I have read "NEC to allow a 50A outlet on a 30A circuit if it's a single outlet circuit ( 210.21(B)(1) ). The only restriction is the outlet is not to have a amp rating less than the circuit. There is no restriction to the outlet being a higher rating than the circuit. But, on circuits with two or more outlets you need to use the values listed in table 210.21(B)(3) which would limit a 50A outlet to a 40A or 50A circuit." There may be also local codes in addition to the NEC. The key factor is a single dedicated socket as opposed to multiple.

The load must conform to the breaker size not the plug if rated higher than the breaker. There are also cases where the breaker is rated higher than the wire rated current such as VFDs and motors where their is a high surge and/or short term peak load.  What I often will do is use an adapter plug to socket if say you have a 30 A socket and want to connect it to a 50A plug with a maximum 30A load.


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## MontanaLon (Apr 23, 2019)

Code? What is code? I guess living in the sticks has its' advantages.


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## matthewsx (Apr 23, 2019)

mksj said:


> Not an electrician, but from what I have read "NEC to allow a 50A outlet on a 30A circuit if it's a single outlet circuit ( 210.21(B)(1) ). The only restriction is the outlet is not to have a amp rating less than the circuit. There is no restriction to the outlet being a higher rating than the circuit. But, on circuits with two or more outlets you need to use the values listed in table 210.21(B)(3) which would limit a 50A outlet to a 40A or 50A circuit." There may be also local codes in addition to the NEC. The key factor is a single dedicated socket as opposed to multiple.
> 
> The load must conform to the breaker size not the plug if rated higher than the breaker. There are also cases where the breaker is rated higher than the wire rated current such as VFDs and motors where their is a high surge and/or short term peak load.  What I often will do is use an adapter plug to socket if say you have a 30 A socket and want to connect it to a 50A plug with a maximum 30A load.



Thanks MKSJ, that's pretty much what I thought. If the outlet is rated higher than the breaker then it shouldn't be a problem. I am a "certified marine electrician" for what that's worth so I know the reasons for codes and try to make sure everything in my shop conforms. I'd hate to have a problem then deal with the insurance company telling me I shouldn't have been enjoying the tools in my shop. It is a dedicated circuit off the sub-panel and the breaker box is right next to the outlet so anyone in the future trying to pull a full 50 amps from it should get a clue real quick.

What I have now is an extension cord that's 30 amp to 50 amp, so basically a really long adapter for my welder. I was thinking I'd install the right plug so I don't have to run the longer cord but after doing a few welds with my Millermatic 150 I think I will hold off. This thing is an orphan and even though it's blue it really doesn't make nice welds no matter what I try . I might just replace it this spring since I have a bunch of projects that require welding and I hate struggling with my tools.



MontanaLon said:


> Code? What is code? I guess living in the sticks has its' advantages.



If the shop were in a detached building I'd probably worry less, but it's right below our bedroom

Cheers,

John


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## Latinrascalrg1 (Apr 23, 2019)

Matt have you ever tried the welder without using the extension cord? If not i think the results may surprise you! Maybe!


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## tq60 (Apr 23, 2019)

Extension cords add voltage loss.

Only use if no other option. 

Only thing that counts is the breaker matches the SMALLEST part of the total circuit.

A 50 amp outlet with number 12 wire has a 20 amp breaker.

We use dryer plugs for welders and a few other items as we pick up the parts at yard sales sometimes.

Some are wired for 20 amps and others for 30 amps.

Inspector may complain about the outlet being not standard but the breakers are correct for the wires as they are the SMALLEST part.

Conduit loading restricts wire size so smaller wire used, and size is suitable for the installed unit.

Larger loads like the 7.5 hp compressor have 50 amp outlet with correct wore and breaker.

Sent from my SAMSUNG-SM-G930A using Tapatalk


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## kd4gij (Apr 23, 2019)

If the capacitors are original replace them and that Millermatic 150 will weld better then most new ones. I have it's big brother


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## MontanaLon (Apr 23, 2019)

matthewsx said:


> If the shop were in a detached building I'd probably worry less, but it's right below our bedroom
> 
> Cheers,
> 
> John


Electricity only causes problems when it is flowing. If you are concerned about it, throw the breaker when you are done. If the wire can take 30 amps, and the breaker is 30 amps and you don't plan on drawing more than 30 amps, how it is connects to the circuit is a minor issue. I mean, as long as it isn't bare wires stuck into a potato, it will be good.

But it is worth having breakers tested when you get to a certain point. As a past firefighter, I have seen a few fires started by breakers that failed to trip when the circuit was overloaded but exactly zero caused by having a circuit with a properly wired but overrated receptacle.

But then, I don't have an inspector looking over my shoulder. I'd be willing to bet 80% of the wiring in this town have never been inspected. You pay your money for a permit, or not and run the wires. Surprisingly, we don't really have that many fires that are electrical in nature.


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## matthewsx (Apr 24, 2019)

kd4gij said:


> If the capacitors are original replace them and that Millermatic 150 will weld better then most new ones. I have it's big brother



I am fighting some weld quality issues, I'll look into that. Funny, I've been working on everything else in the shop but haven't touched the welder....

Thanks,

John


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## matthewsx (Apr 24, 2019)

MontanaLon said:


> Electricity only causes problems when it is flowing. If you are concerned about it, throw the breaker when you are done. If the wire can take 30 amps, and the breaker is 30 amps and you don't plan on drawing more than 30 amps, how it is connects to the circuit is a minor issue. I mean, as long as it isn't bare wires stuck into a potato, it will be good.
> 
> But it is worth having breakers tested when you get to a certain point. As a past firefighter, I have seen a few fires started by breakers that failed to trip when the circuit was overloaded but exactly zero caused by having a circuit with a properly wired but overrated receptacle.
> 
> But then, I don't have an inspector looking over my shoulder. I'd be willing to bet 80% of the wiring in this town have never been inspected. You pay your money for a permit, or not and run the wires. Surprisingly, we don't really have that many fires that are electrical in nature.



The local building inspectors went to jail a few years before we moved here so nobody pulls permits unless they absolutely have to. My philosophy is I can work on anything inside my own home but I want the work done in a way that the next guy looking at it won't say WTF. I ran a small engine repair shop and the kinds of "repairs" I had to fix were mind boggling....

Thanks,

John


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## projectnut (Apr 24, 2019)

As I understand it the only difference between a 30 amp plug and a 50 amp plug is that on the 30 amp the neutral and ground are combined.  On a 50 amp plug they are separate. 
We recently did a remodel of our kitchen including a new range.  The old range had the 30 amp style plug, but since the time it was installed the local electrical codes have changed.  The combined neutral and ground is no longer allowed.  The new range is now wired with a 50 amp style plug and receptacle.  Fortunately when the house was built the contractor wired the range with the proper gauge 4 conductor wire.  The new codes must have already been in the works since the 4th conductor was folded back and taped off on both ends.


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## mksj (Apr 24, 2019)

It is not uncommon, to run heavier extension cords/wire to account for voltage drop over the length of the wire. My compressor (5 Hp, 24A running current) uses a 50A plug with a 8 gauge 25' welding extension cord rated at 40A. In this case, I am running a 50A breaker with #6 wire to the socket, with a 50A 3 prong socket. Technically you are limited by the rating of the extension cord. As mentioned, the breaker may be up to 125% of the motor nameplate current and round up to the nearest breaker size. There are some exceptions as to the breaker sizing. The breaker protects the wire, the motor has a separate thermal overload at the compressor. If you were to move, I still would replace the socket with a 30A rated one, because one would assume a 50A socket would be on a 50A circuit. If you have a long wire run to the socket, then you will get a voltage drop to the socket. In addition, although a socket plug may be rated at 30A, it is based on a continuous use amperage of 80% for a branch circuit (24A). If your welder is exceeding this load for any length of time, then you could overheat the wire to the socket.

As far as plugs, the neutral and ground are NOT connected at the plug, or for that matter anywhere but the main service panel. Plugs come in different configurations, but the neutral is either not present (3 prong 230VAC) or present as a separate connector (4 prong 230 VAC). The neutral is only required on 230VAC if you need to pull a 120VAC circuit, often seen on appliances.


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## markba633csi (Apr 24, 2019)

US electrical hardware is the sloppiest fitting stuff in the world.  I shake my head every time I do conduit work.  And the connectors are a horror show too.  It's a wonder there aren't more fires.
You're welcome.
Mark


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## Nick Hacking (Apr 24, 2019)

In the UK it is now, strictly, illegal to use electrical installations that have not been checked and passed by a suitably qualified electrician. You can do the work (say adding a new ring main circuit) yourself but cannot use it until it has been passed. Good news for electricians and significant with regard to insurance claims for electrical fires. I can see the sense in it but at the same time it feels like another intrusion by Nanny State.

If I plug a 20-foot extension into a wall socket and run five four-way adapters off that to run twenty power tools, that's fine because it's all consumer equipment. If I open the distribution box and run a loop of twin-and-earth to a pair of sockets, that needs to be checked before use.

Kind wishes,

Nick


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## Bi11Hudson (Apr 24, 2019)

Codes, for any craft, are usually frustrating as hell. But they exist for a valid reason. Look at a mobile home or any other "submain" circuit. The 240 volt circuit will have a fourth wire, where the neutral and the ground are separate conductors. There is a valid reason for requiring it, although in many(most?) cases it doesn't really matter. 

Look at http://www.hudsontelcom.com/uploads/ShopElex.pdf to go a little further with that subject. The big issue here is the plug. A normal 50 amp plug hooked up to a 30 amp circuit is not in violation of *common sense*, But if someone else comes along later and finds the 50 amp plug and thinks it should have a 50 amp breaker, that's a fire waiting to happen. That's why most codes are concerned with the idea. Common sense isn't all that common. The National Electric Code, NEC, is actually the private organization known as the NFPA, the National Fire Protection Agency. A city, county, or state code is a copy of the NEC plus any local modifications.

My suggestion would be to run down to the local hardware store and get a "dryer" cord. And then mount a dryer plug (30 A) to hook it into. If you trip the breaker, you need a bigger circuit. Stash the original cord so you can convert it back to OEM in the future if need be. The 50 amp plug is the same as a "range" connection, BTW. The 4 wire plugs and caps and pre-made cords are available at most any mobile home supplier, if that's what tickles your fancy.

Bill Hudson​


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## matthewsx (Apr 28, 2019)

I think what I will do is install the plug next to the electrical box. 

Then label it as 30 amps. This plug is identical (physical dimensions) to the 30 amp plug except the prongs are vertical rather than horizontal. It will be wired to a 30 amp breaker. The sub panel is also running off a 30 amp breaker. So, for someone to overload the branch circuit they would have to change the both breakers.

Then, when I sell the house and move out I can pull the sub panel and leave just a 30 amp dryer outlet.

Cheers,

John


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## Flyinfool (Apr 30, 2019)

One thing to remember is that electricity can not tell the difference between an extension cord and the wires in the walls. A foot of 12ga is a foot of 12ga.Voltage drop starts to happen from the point the wire is attached to the breaker. (Actually it starts from the point of connection to the transformer out on the power pole down the block but you have no control of what is outside your house.) Where I work there was one customer that kept burning out motors on a machine. We finally made a road trip to their place and found that they were plugging into a 15 amp outlet that was around 250 to 300 feet from the breaker and wired with 14 ga wire. That is no different that having the outlet right below the breaker panel and running a 250 ft 14ga extension cord. They were only getting 98 volts at the outlet and that is what was burning out the motors.

I replaced the 6ft 10ga power cord on my welder with a 20 ft 6ga cord so that it will reach anywhere in my shop. I also have a 50 ft 6ga cord to be able to get outside with it. Wires can only be to small, it is not possible to have an electrical problem from to big of a wire.


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