3 wire 220v into a 4 wire receptacle

[summit151]

Hello i am in the middle of wiring my shop. I would like to put one main 220v plug in for a welder and a air compressor. But to run my welder i need a 4 wire 40 amp plug and the air compressor is only a 3 wire 20 amp 220. The air compressor will always be plugged into and i just want to unplug it and plug in the welder when I need it. My question is can you safely run a 3 wire 220 off a 4 wire receptacle?

 

[theoldwizard1]

... to run my welder i need a 4 wire 40 amp plug and the air compressor is only a 3 wire 20 amp 220.
...
My question is can you safely run a 3 wire 220 off a 4 wire receptacle?

Yes. Install a 4 prong plug on the compressor. Do not connect anything to the neutral terminal in the plug.

 

[summit151]

Ok that is what i was planning on doing. Just making sure it will no affect anything

 

[pattenp]

There is no such animal as a 40A plug. You need to use a 50A plug. If the compressor came with a factory cord with a 20A plug on it then you really shouldn't put a 50A plug on it and plug it into a 40A or 50A circuit. Does the compressor motor have its own overload protection?

Plug chart....
http://www.stayonline.com/reference-nema-straight-blade.aspx

 

[Speedy Petey]

Just do the right thing and install the proper circuit for each. They are two different animals.

Are you SURE the welder requires a 4-wire circuit?

 

[summit151]

sorry yes it is a 50 amp stove receptacle. what is the main reason why you can not use a 20 amp compressor on it to?

 

[theoldwizard1]

sorry yes it is a 50 amp stove receptacle. what is the main reason why you can not use a 20 amp compressor on it to?

The pigtail from the plug to the motor and the wire inside are rated for 20A. If for some reason they start drawing much more than that, but less than the circuit breaker/fuse, they will overheat and could catch fire.

 

[summit151]

I am pretty sure the motor does have a overload protection

 

[sberry]

What welder is this? I see Speedy asked the same question.

 

[sberry]

The pigtail from the plug to the motor and the wire inside are rated for 20A. If for some reason they start drawing much more than that, but less than the circuit breaker/fuse, they will overheat and could catch fire.

The wire needs to be heavy enough to be connected to the 50A,, which would be a number 12. The breaker in this case des not provide for overheat or overload, this is the job of the thermal overload and by design in the fact that the unit only draws 20A,,, it comes with a cord that wont be overloaded by the unit.
The breaker here is an off/on switch and for short circuit protection which involved hundreds,,, or in some cases thousands of amps in a fault.

 

[bloomingtonmike]

Post up pics of the plate on the welder. Make and Model number at least

 

[theoldwizard1]

Old School. This will solve your problem (if you can find one). Cooper-Bussmann SKA. You can even use "screw in" breakers.

EDIT: Wow, found one on eBay cheap !

 

[sberry]

I want to go back to this as its not very well understood. I am not a real expert either but we need some theory followed with code.

 

[wyliesdiesels]

Welder circuits have special rules for sizing wire and breaker and are based on duty cycle. Highly unlikely welder would need a neutral unless maybe it has a spool gun or some other 120v device. We need to know the model of the welder to give a proper answer.

Circuit for Compressor on the other hand is sized based on motor HP. We need to know HP rating or compressor model to give a proper answer!