4 prong outlet--3 wire motor

[James E]

My new 240 outlets are set up for four prong plugs. Of course, my compressor and the motor on my lift (both using 240) have 3 wires.

When wiring up the plugs for the compressor and lift, I was under the impression that the neutral prong would not be used in this situation--just two hots and the ground--the neutral only being necessary for appliances that have the need for 120 power in addition to the 240 running the main appliance.

So, if I'm using a four prong plug on a three-wire motor, I can use a 3 wire cord from the motor to the plug and then not use the neutral prong on the plug, just the two hot wires and the ground.

Is that correct?

 

[Aceman]

Yep.......

 

[James E]

Short, sweet and the answer I was looking for.

Thank you.

 

[Kerryp]

Sorry to hijack this thread, but I have a question directly related to this exact scenario. I might have screwed up bad today. I connected the ground on the compressor to the white neutral wire. the motor did about 3 revolutions then quit and would not start again. There was no sparks, noise or smoke. I will go back and wire it properly tomorrow but I would just like to know what happens to the motor when its wired this way. I hope I didn't fry anything!!

 

[avc8130]

The neutral and ground are tied together at the box. I am not sure if it would matter.
ac

 

[hillbilly1]

Sorry to hijack this thread, but I have a question directly related to this exact scenario. I might have screwed up bad today. I connected the ground on the compressor to the white neutral wire. the motor did about 3 revolutions then quit and would not start again. There was no sparks, noise or smoke. I will go back and wire it properly tomorrow but I would just like to know what happens to the motor when its wired this way. I hope I didn't fry anything!!

If you connected the ground (green wire) from the compressor cord to the white wire that is connected to the neutral bar in the panel, then no, it did not screw up the compressor.(it needs to be changed though) But........ if you connected the white wire from the compressor cord to the white wire connected to the neutral bar in the panel, and the compressor is 240 volts, it probably tripped the overloads on the motor or motor starter due to trying to run on 120 volts. Either the motor will have an automatic reset that will allow the motor to be restarted in a few minutes, or it will have a red button on the rear of the motor that will have to be pushed to reset. If it has a magnetic starter, (unlikely, because 120 volts would probably be insufficent to pull in the coil to do anything) the reset button would be on the front of that enclosure.