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Electrician needed! Help Wiring 220v Compressor... 3 wires to 4 dryer setup


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Ok, So I was at sear a few months ago looking at compressors and stumbled on a great deal.

I was looking to get a black 40Gal 110/220 when I noticed they had the black 80Gal 220 cheaper.

I guess they miss printed the add and had to actually sell at the price, needless to say I picked it up.

I do not have a 220 outlet in my garage so I picked up a 50 foot line and placed my compressor inside my laundry room.

My dryer has a 4 prong 220 30A plug it goes to so I figure I will use that to run my compressor as I will not be constantly running the tank and it will only be plugged in when I am using it. This will work for sure the only thing is my compressor has only 3 wires....

I really do not want to mess up my new compressor if I don't have to and would like to do it correct without burning up the motor.

It is 220 only and here are pics of it.

The Motorpost-85933-143139147442_thumb.jpg

The compressorpost-85933-143139147449_thumb.jpg

And here is the junction box post-85933-143139147451_thumb.jpg

There is only a black a white and a green.

The green goes to the frame/ground

The other two go into the pressure switch.

Do I just hook up the black to black white to white discard the red? Or does the red have to connect with either the black or the white?

Note I do not have another 220 plug in my house and it is base housing so I cannot drop one from the fuse panel.(hard wire it)

P.S. there are no instructions for connecting it.

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The four wire dryer outlet has two "hot" wires (usually black and red), one white neutral wire, and a green ground wire. The white neutral is there to provide 120 v for the timer motor in the dryer (the voltage between the white and either hot wire is 120, between the two hot wires is 240). Your compressor only needs to be connected to the two hot wires and the ground, so get a four prong plug that matches the dryer outlet, leave the neutral prong unconnected, wire the compressor ground to the ground prong, and wire the other two hot wires to the hot prongs.

This works, and frankly I've done it myself, but there's one significant problem. The dryer outlet is likely a 50 amp circuit. The compressor wiring is probably only rated at 20 amps, so you are not adequately protected for the run from the plug to the motor. A far better solution is to simply install a new 20 amp (or whatever the compressor requires) breaker in your panel box and run a dedicated circuit to it. This is not at all difficult to do, but obviously requires the proper attention to detail and safety. If you are not comfortable doing it, get a professional.

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Ok, ...I do not have a 220 outlet in my garage so I picked up a 50 foot line and placed my compressor inside my laundry room....

Why not just install a 220V outlet in the garage? If you have a breaker box there already, then you probably have the room to add a 220V outlet. It's the right way and safeist way. For what you paid for the 50' cord you can install an outlet. The long cord also taxes the circut too. Then it's always there for you when you need it without having to mess around with plugging it in all the time.

If the breaker is a 50A for your dryer and the compressor has a problem, you have a good chance on the compressor starting a fire. I DO NOT reccoment this! There is a reason the dryer has a 50A breaker, this is not the right solution. Kind of like putting a larger fuse in your car because the radio shorts out, sure the fuse won't blow, but something will, probably the wiring. Fix the radio, not the safety device!

Edited by Amphicar BUYER (see edit history)
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Dryer and stove wiring have to have a separate neutral and ground wire. They are all kind of the same, but the neutral is used to return the current from 110V items in the device and have a separate ground to protect you. Before the same wire was the ground and neutral, but if something went wrong with the neutral wire then you could have dangerous voltage on the metal surrounding the device.

I believe the red and black wires are the 2 hots and the white is the neutral (which is not used on the compressor since there are no 110V circuits). I am pretty sure by code ( I am not an electrician) the green wire is the ground wire the white wire is the neutral and the black or other color wire are hot wires. I can not be 100% sure cause I can not see the end of the cord you have.

Here is a link to some pictures that should make sense to you.

Dryer wiring

If you are confused then STOP and get someone in that understands electricity.

I need to take a second and correct an error in another post.

This statement install a new 20 amp (or whatever the compressor requires) breaker above is wrong. Breakers are install to protect the wire. The size of the breaker is based on the gauge of the wire. The wire gauge is selected to handle the device at the end of the circuit.

It is important to understand the breakers are NOT there to protect the device at the end of the wire. This is a very wrong assumption by many.

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If you are confused then STOP and get someone in that understands electricity.

I need to take a second and correct an error in another post.

This statement install a new 20 amp (or whatever the compressor requires) breaker above is wrong. Breakers are install to protect the wire. The size of the breaker is based on the gauge of the wire. The wire gauge is selected to handle the device at the end of the circuit.

It is important to understand the breakers are NOT there to protect the device at the end of the wire. This is a very wrong assumption by many.

The best advice! 110v can kill you (it really the amps not the voltage) but 220v will ruin your day (if not end them). Just get a pro to do it correctly and sleep well. My dad was a master electrician for 40 years and nobody ever regretted spending the money for his expertice! If you burn down your house and the investigators discover you had new wiring not to code. They can negate the entire claim as negligence.

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I need to take a second and correct an error in another post.

This statement install a new 20 amp (or whatever the compressor requires) breaker above is wrong. Breakers are install to protect the wire. The size of the breaker is based on the gauge of the wire. The wire gauge is selected to handle the device at the end of the circuit.

It is important to understand the breakers are NOT there to protect the device at the end of the wire. This is a very wrong assumption by many.

Sorry if in my haste to respond, I was not completely clear. The compressor has a cord sized for the amperage draw of the unit. A 20 amp compressor with an internal fault will trip a 20 amp breaker. It may NOT trip a 50 amp breaker, at which point bad things will happen.

Interestingly, Amphicar Buyer correctly pointed this out in his first post then confused the issue in his subsequent post.

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Hire a licensed electrician. To many do it yourselfers have burned down their garages and houses thinking they can save a buck. Get the 220 in the garage where it belongs. I would not put my collection or home at risk. Good luck

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It can be done by an amateur.

I ran 220 from my house to my shop, about 100 ft. First, I pulled a permit. Then I asked, at the electrical supply house, what I would need to do the job. They were very helpful, told me what gauge wire I would need, etc. I ran 2 hots, one neutral and one bond. There is a separate ground at the shop with a copper rod driven into the ground. A buddy gave me 100 ft of Carlon PVC conduit. It all passed inspection on the first try. Local codes may differ. I would never try this without a city or county permit. It's a PITA, but at least you know it will not kill you or burn your stuff to ashes

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Hire a licensed electrician. To many do it yourselfers have burned down their garages and houses thinking they can save a buck. Get the 220 in the garage where it belongs. I would not put my collection or home at risk. Good luck

This is so simple even a cave man could do it. Or you could just P**s your bucks away hiring it out................Bob

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My dad is coming out here in a few weeks, he said he would drop a line directly from the box into the garage. Here is the thing I will still need to hook up the plug, which I will keep a dryer set up so the next sucker who lives here does not blow up any tools. The motor is thermally protected and since I am using a "dryer" plug I can assume can handle the amperage. Like my first post said the breaker dedicated to the dryer is 30A and my dad said this plug would suffice untill he can drop a line in the garage. I did understand the whole 220 over the 2 hot and 120 over the hot and ground, the part that got me was in the switch there is only a white black and green. The green obviously is ground as it grounds to the metal on the compressor and the other two are just white and black. The red wire in photo is the 4 prong dryer hookup plug. The motor says one way and I did not want to reverse the polarity if that is even possible, in the instructions it does not label any of these wires nore does it tell you which prong gets 220-240. The 50FT of line is pnumatic not electrical.... that would be expensive and dangerous. At this point I think I will wait till he makes it out here to drop the line since I have one more spot on the panel.

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To make it a little less confusing, tape the white wire in the compressor box red. It doesn't matter if you reverse the red and black, the motor will only run in one direction. It's like if you have a drill with a two prong plug, either way you plug it in the drill will run forward. Lose the white wire in the cord. attach the red and black wires to the slanted prongs in the plug (cap) on one end and the ground to the "L" shaped prong. In the compressor box connect the red and black from the cord to the red (taped) and black in the box and the ground to the ground screw.

The nameplate says the compressor is 15 amps so you're taking a chance running it on a 30 amp receptacle. you'd probably be better off just running a 15 amp 220 outlet or run the 30 amp 4 wire cord to a small sub panel in the garage.

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...the part that got me was in the switch there is only a white black and green. The green obviously is ground as it grounds to the metal on the compressor and the other two are just white and black. The red wire in photo is the 4 prong dryer hookup plug. The motor says one way and I did not want to reverse the polarity if that is even possible, in the instructions it does not label any of these wires nore does it tell you which prong gets 220-240. The 50FT of line is pnumatic not electrical.... that would be expensive and dangerous. At this point I think I will wait till he makes it out here to drop the line since I have one more spot on the panel.

The dryer requires 120V as well as 240V. That's why there's an additional wire. The compressor only requires 240V. ASSUMING the dryer plug is wired correctly, the red and black should be hot, the white neutral. If so, then the black and white compressor wires go to the red and black wires in the plug. Green ground to green ground and you're done. If the dryer is only 30 amps, this is no problem. There is no polarity issue with the black and white compressor wires - they can be connected to the black and red plug wires either way. This is AC not DC.

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I was taught to run a line direct from the breaker of proper size to the device, in your case the compressor motor. Using the wire size the code calls for. Every time you put something ie. a plug, junction box, wire nuts(especially not taped)and splices between the breaker and device you increase the possibility of a potential problem. Just my humble thoughts. --Bob

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[Thanks for the comments guys. Looks like I will wait for my dad to come out, he is the contractor. I'm just the mechanic :)

Thats a good plan.

Here in Australia we dont have 110 volts, we have 220 - 240V for everything and I can tell you that if you get hit with 220v and 15 amps there is a good chance they will be talking about you in the past tense saying what a good guy you were etc. and buying flowers.

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