wiring a 208-230 air compressor

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  #1  
Old 05-04-06, 11:17 AM
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wiring a 208-230 air compressor

Hello,

I have a Bel aire 2-stage air compressor. The tag reads 208-230 Volts 1 ph. 22amps.
I’m I correct in using number 10 awg wire with a 30-amp double pole breaker?

Also the motor came prewired black, white and a ground (the motor is grounded). I read the manual and it states where the incoming hot-wires go but I see no way to connect the incoming ground. I also noticed that the cable going to the motor is 12-2 awg , but yet the tag reads 208-230 Volts 1 ph. 22amps. I’m running wire in conduit straight to the breaker (the subpanel is only 5 feet away from the compressor).

So my questions are:

I’m I correct in using 10 awg with a 30-amp double pole breaker as the supplied power?
What do I do about the ground?

Here is a pic of the compressors wiring

 
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  #2  
Old 05-04-06, 11:59 AM
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> 208-230 Volts 1 ph. 22amps.
> Am I correct in using number 10 awg wire with a 30A double-pole breaker?

Yes.

> I see no way to connect the incoming ground.
There should be a lug or green screw.

> I also noticed that the cable going to the motor is 12-2 awg,
> but yet the tag reads 208-230 Volts 1 ph. 22amps.
Manufacturers can use any wire size that passes the UL tests.

Don't worry about it.

> What do I do about the ground?
Find a place to land it.

Your picture is from the wrong angle.
The green screws should be at the bottom of the control where the wires come in.
The photo shows only part of the top and one side.
 
  #3  
Old 05-04-06, 12:12 PM
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The rules for electric motors are a bit more involved but yes, a 30 Ampere circuit is probably sufficient for this unit.

Your picture is somewhat confusing as is your description. On the left side of the pressure switch is a flexible cable and on the right side is an EMT connector, short piece of EMT, an EMT coupler and then more EMT. I see two connections to the pressure switch, one for each line (or "hot") connection.

The EMT (thinwall conduit) looks like someone cut a piece too short and rather than properly cut a new piece just added a short stub and coupler. Please tell me this is NOT the supply from the panel.

I also hope that you are not using the word "ground" in place of the word "neutral".

The proper wiring for this machine is a black lead coming from the circuit breaker pole connecting to the left-hand main bus in the panel and a red lead coming from the circuit breaker pole connected to the right-hand main bus in the panel. These two leads will connect to the unterminated points (as pictured) on the pressure switch. It is not important which color goes to which terminal in the switch but to follow convention you would connect the black to the left-hand terminal and the red to the right-hand terminal.

You also need a green wire connected to the equipment ground bus in the panel and to the frame of the machine at the compressor unit. If this is a SERVICE panel you are connecting to (that is, a panel connected directly to the electric meter) the equipment ground bus could also be the neutral bus.
 
  #4  
Old 05-04-06, 12:13 PM
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Yeah there is a green screw at the bottom, but the ground from the motor is on it. The instructions for the wiring says not to double up the wiring. Thats why I said I could not find a place to ground it. I should have said I could not find a separate ground connection.

Thanks for responding.
 
  #5  
Old 05-04-06, 12:17 PM
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> Yeah there is a green screw at the bottom,

Did you but this unit new?

> but the ground from the motor is on it.

There should be two green screws side-by-side.


> The instructions for the wiring says not to double up the wiring.

Correct.

> That's why I said I could not find a place to ground it.

Look again.


> I should have said I could not find a separate ground connection.

If the screw is missing, but the hole is there, the 10-32 broadhead machine screw was lost and you can supply a new one.
 
  #6  
Old 05-04-06, 12:21 PM
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Originally Posted by furd
The EMT (thinwall conduit) looks like someone cut a piece too short and rather than properly cut a new piece just added a short stub and coupler. Please tell me this is NOT the supply from the panel.
What is the actual problem? Sometimes it happens that a run is 10'6". I wouldn't mind if the last section was FMC to reduce the transmission of vibrations.
 
  #7  
Old 05-04-06, 12:23 PM
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This unit is brand new. I will check again but I sure I did not see it. But in my being in love with having a new toy I will check again. By the way what is wrong with using the coupler with the EMT? I thought thats what it was for (to join to pieces together. I ran out of conduit and thought this would be okay because the wires are still protected plus its indoors. If its wrong I will change it.

Furd said: "I also hope that you are not using the word "ground" in place of the word "neutral".

From my understanding all I need it two hots and a ground for this unit.

Thanks guys
 

Last edited by kabwe; 05-04-06 at 01:02 PM.
  #8  
Old 05-04-06, 04:57 PM
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Originally Posted by bolide
What is the actual problem? Sometimes it happens that a run is 10'6". I wouldn't mind if the last section was FMC to reduce the transmission of vibrations.
Absolutely correct, a piece of flexible conduit should be used to allow for vibration.

Yes, Kabwe a neutral is NOT needed in your case but sometimes DIY'ers confuse neutral with ground and also wonder why a neutral is not needed with a 240 volt load.
 
  #9  
Old 05-04-06, 06:01 PM
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Okay thanks. I do know a little about electrical but I come here anyway, because a little can get you into a lot of trouble.
 
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