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kleen56 10-30-2009 09:04 PM

220 V issue
 
I have an air compressor for my garage that runs on 220V. The plug on the compressor is for a 20 amp design and ran good at my other house. I have a new home that doesn't have the 220V in the garage, but has the wash room with a 220V outlet for a dryer. I was told that plug is a 30 Amp. Here's the electrical problem... Can I run a plug from the 30 amp to a 20 amp air compressor without having any issues? I could run a new 220V line with a 20 amp breaker but they want like $400-500 to run a line. My air compressor doesn't cost that much :welcome:

Any electricians that give some advice? Thanks.

Nim-Rod 10-30-2009 09:13 PM

I am not an electrician, however, you can run a 20 amp compressor on a 30 amp circuit without a problem. Circuits are designed with the appropriate breaker to protect the wiring and not the equipment on it. The compressor will run well on the dryer circuit.

302 Z28 10-31-2009 08:05 AM

That is perfectly acceptable, but you must run the properly sized wire for that 30 amp breaker to your 20 amp plug. A 30 amp breaker requires #10 AWG wire.

Vince

kleen56 10-31-2009 09:36 AM

Thanks for the info. I noticed they sell the plug and wire in 6 foot length specific for dryers. I could buy additional 10 gauge 220 wire and make an extension cord to my air compressor. I figure the cost with wiring and a plug will be about $60 which is better than $500. It'll be nice to be able to use my air tools again as well.
Ed

I'm confused now, I got this from an old post in here. The guy is a licensed electrician and quotes," It is a dangerous practice to run a plug on a circuit that it's not intended for such as putting a 30 amp drier plug on a 20 amp piece of equipment. This is a violation. You must use the correct plug for the circuit and not go over or under. I'm a licensed electrician by trade.[/QUOTE]

302 Z28 10-31-2009 10:28 AM

If you try and run a 30 amp rated device from a 20 amp plug you will have problems. Your compressor has a 20 amp plug. It does not draw 20 amps, there is a safety margin built into the plug size and wire size. Also the plug configuration excludes you plugging that 20 amp plug into a 30 amp receptacle. The circuit breaker is there to protect the wire, not the device at the end of the wire.

Vince

scotzz 11-04-2009 04:45 PM

Quote:

Originally Posted by kleen56
Thanks for the info. I noticed they sell the plug and wire in 6 foot length specific for dryers. I could buy additional 10 gauge 220 wire and make an extension cord to my air compressor. I figure the cost with wiring and a plug will be about $60 which is better than $500. It'll be nice to be able to use my air tools again as well.
Ed

I'm confused now, I got this from an old post in here. The guy is a licensed electrician and quotes," It is a dangerous practice to run a plug on a circuit that it's not intended for such as putting a 30 amp drier plug on a 20 amp piece of equipment. This is a violation. You must use the correct plug for the circuit and not go over or under. I'm a licensed electrician by trade.

[/QUOTE]

I think that quote is from a thread I was involved in last year. I spliced in a standard dryer cord to a 10 gage line I ran into the garage for a welder (20A). The dryer line is on a 30A breaker meaning that the welder (or anything else not rated at 30A on that line) may not be protected. But, this is the same as probably every appliance or power tool you plug into a 120v outlet so to me it's a moot point. In my case, the 10gage line ends in a 20A plug but wire size is correct for the 30A breaker. I got some crap for this setup but I maintain that as long as the wire size is correct for the breaker and workmanship is correct it is safe. I included pictures of my set-up in that post.

302 Z28 11-05-2009 07:17 AM

[/QUOTE=scotzz]I think that quote is from a thread I was involved in last year. I spliced in a standard dryer cord to a 10 gage line I ran into the garage for a welder (20A). The dryer line is on a 30A breaker meaning that the welder (or anything else not rated at 30A on that line) may not be protected. But, this is the same as probably every appliance or power tool you plug into a 120v outlet so to me it's a moot point. In my case, the 10gage line ends in a 20A plug but wire size is correct for the 30A breaker. I got some crap for this setup but I maintain that as long as the wire size is correct for the breaker and workmanship is correct it is safe. I included pictures of my set-up in that post.[/QUOTE]

Again, the circuit breaker or fuse is not to protect the welder or anything else that is hooked up to the wire. The breaker or fuse protects the wire. That is why a circuit is first sized for the anticipated load. Then the circuit breaker is selected as is the proper wire size for the anticipated load. Wire size is selected at 125% of max load.

Vince

cjperotti 11-05-2009 04:50 PM

Your compressor has a trip breaker installed as federally required by law for the appropriate amperage. Connecting it to service line with the higher amperage as discussed will not violate any laws as it will will still function as it was designed without overloading the circuit.

ford2go 11-07-2009 01:11 AM

Hopefully you did a good job in splicing the extension wiring. I don't think that ou can have any kind of a permanent installation where both ends plug in. So, it would be like an extension cord.

I also don't know about what a good splice would be. I would imagine that properly sized wire nuts (Scothchlocks or equivalent) would work. To be really safe, you could make the connections inside of a metal electrical box and make sure that you ground the box. I'm not familiar with 220v dryer plugs, but newer designs should include a ground wire. You can put a plain metal cover on the box.
You should also use strain reliefs on both ends.

I have fixed more than one extension cord with wire nuts and electrical tape, but you have some heavy duty stuff here.

It would be easier to get 10 ga UF 3 wire plus ground cable to make the extension. Otherwise you have to keep the wires together somehow.

Depending on how your house is laid out, it might not be that difficult to just run a circuit from your fuse box. If you can use flexible cable rather than conduit, it could be fairly straight forward. You can find electrical code books at the library.

scotzz 11-07-2009 05:16 AM

Quote:

Originally Posted by ford2go
Hopefully you did a good job in splicing the extension wiring. I don't think that ou can have any kind of a permanent installation where both ends plug in. So, it would be like an extension cord.

I also don't know about what a good splice would be. I would imagine that properly sized wire nuts (Scothchlocks or equivalent) would work. To be really safe, you could make the connections inside of a metal electrical box and make sure that you ground the box. I'm not familiar with 220v dryer plugs, but newer designs should include a ground wire. You can put a plain metal cover on the box.
You should also use strain reliefs on both ends.

I have fixed more than one extension cord with wire nuts and electrical tape, but you have some heavy duty stuff here.

It would be easier to get 10 ga UF 3 wire plus ground cable to make the extension. Otherwise you have to keep the wires together somehow.

Depending on how your house is laid out, it might not be that difficult to just run a circuit from your fuse box. If you can use flexible cable rather than conduit, it could be fairly straight forward. You can find electrical code books at the library.

The feeder line to the garage is BX and is wired in just like a permanent installation. It goes into a metal junction box where it is connected to the dryer cord with wire nuts. The dryer cord does have a strain relief where it exits the box. It functions like an extension cord. I would have wired the line directly to the main panel but there is no space. I'm Ok with this set-up for the limited time I will be using the welder, especially since duty time is very limited with this type equipment. If I were going to run something with a longer cycle time (such as a compressor) I would not use this set-up.


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