I am trying to wire in my new compresser that I got and am haveing trouble with the elec. conection.The motor is a7hp. 240 v,15 amp,now 240 is 3 wire,2hot and 1neutrel but the motor has only 2 wires from the pressure switch.How do I hook up the power from the elec panel?The pressure switch has 2 terminels marked line1& line2,I supose that I would make them hot,but where does the neutrel wire go and why is the no neutrel to the motor? I hope that this is understandable.

 

the two hot wires got to the switch abd the "neutral" wire is a ground hope that helps

 

Look at your nameplate on the motor to see the wiring connections, if not there, pull out the instruction manual. Not being able to see your unit, I will just add this. A 220 V single phase motor from the factory should have two black wires and a green, not a white. IF they used a SJ power cord coming out of the motor, then it will have a black , white, and green wire, and if that is the case, then the white should have black paint or electrical tape put on it, to make it known it will be a line(hot) conductor. If the motor is a dual voltage 120/240 it will have a nuetral, with a diagram on the nameplate showing the connections for low 120/high220 voltage ,hook ups. Sometimes they may use a red and black "hot" lead configuration on straight 220 motors. A 220V single phase motor has no need for a neutral, only two hots and a green equipment grounding conductor. My 7 hp compressor pulls 22 amps, so I wired it to a magnetic starter using the pressure switch to control the contactor on the starter only. To use the two terminal pressure switch on a 220 v unit, looks like you will be breaking one side of the 220 line only, not ideal for larger motors, but will work. If you are not completely confident of your electrical skills, be safe and hire a electrician, or maybe you have a buddy that knows someone that will hook it up for a cold beer. . It aint work getting hurt over, jmo, good luck

 

I had the same problem and talked to a couple electricians. The conclusion was to wire the 2 hot wires from the breaker panel to the leads opposite from the motor leads on the pressure switch. The ground (bare copper) and the white (common) from the breaker box are wired to a common ground terminal on the pressure switch case. I hope this helps.

 

My vote is, don't connect the white wire to ground. All you want is the two lines and ground. If you tie neutral to ground, you'll create a ground loop, which isn't a good idea.

 

Aren't the common and ground wires essentially connected in the breaker box anyway, or at least both are connected to the box frame?

 

In a main service entrance panel common and ground share a connection,,, but in a subfed panel they would be seperate. The problem with using the wrong color wires, as was alluded to by Greg is that at some point someone may come along and assume something just due to the color. If you have to use a white for a different purpose clearly remark it with tape. Your comp uses no neutral, only 2 current conductors and ground which should be hooked securely to the machine frame, prefferably on a provided screw. And remember,, if the power comes from a sub connect grd to equipment grounding bar not neutral.

 

I assume it is a single phase compressor. If so, 2 hot wires go to motor, one grounds to the compressor chassis. There is probable a bolt for this somewhere in the box on the compressor. If three phase, whole new ball game.

 

The pressure switch case should have a ground screw on it inside the covered area.