50 amp plug on 30 amp circuit

matthewsx

matthewsx

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

Cheers,

John
 
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
 
If the capacitors are original replace them and that Millermatic 150 will weld better then most new ones. I have it's big brother
 
matthewsx said:
If the shop were in a detached building I'd probably worry less, but it's right below our bedroom:grin:

Cheers,

John
Click to expand...
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.
 
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
Click to expand...

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
 
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.
Click to expand...

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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