240 Volt Air Compressor Hookup

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  #1  
Old 08-15-07, 04:39 PM
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240 Volt Air Compressor Hookup

Folks,

I need a sanity check here.

Background: I'm installing a new Ingersal Rand (I/R) Air Compressor Model SS-5 with a 5 HP electric motor. The motor is connected to a pressure switch. The motor and switch are 230 volt single phase 60 Hz (230/1/60). The motor is rated at 28 amps. So, adding 1.5 times that I get 42 amps. I've got a double pole 50 amp breaker, a #8 AWG, 3-wire cable. (#8-3). The run is less than 40 ft, probably about 30 ft. The #8 AWG cable I bought has 1 red, 1 black, 1 white and a ground wire. The comrpessor/switch has 1 white, 1 black and one green. The green wire out of the motor wire is screwed into the switch box (ground). There is little to none documentaiton on the switch/motor wiring. I/R won't offer any support other than to say call a qualified electrician. This can't be that hard here.


Questions: As I understand it, in order to get the 230 volts to the motor I need to run the black and red, one each out of the double pole breakers and tie them to the black wire in the switch on the compressor, right? Then, tie the #8 AWG white to the white in the switch box. The white should be tied to the neutral bar in the panel. The bare ground to the neutral bar in the panel and to the switch box casing on the compressor. Does this all sound right to you?


Summary

Double Pole 50A Breakers red & black wires -> switch box black wire.

Nuetral bar in panel white wire -> switch box white wire.

Neutral bar in panel bare ground -> switch box casing


Thanks in advance for any help or opinions.

Jimmee
 
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Old 08-15-07, 04:49 PM
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The short answer would be no. As soon as you connect the two legs of the 240 volt breaker together you create a dead short.

You bought the wrong wire. Do not use the white wire in your cable at all. You don't need it. The white wire would be used if the air compressor was 120/240 volts. But it's only 240 volts.

The red cable wire gets connected to either the white or black motor wire and the black cable wire gets connected to the other motor wire.

Make sure that the ground gets connected all the way through.
 
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Old 08-15-07, 05:38 PM
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I see said the blind man...thanks Bob!!!

Jimmee
 
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Old 08-15-07, 05:39 PM
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Cap the white wire at the motor end. Do not cut it short as it may come in handy at a later time.

At the panel end, connect the white wire to the neutral buss or cap it.

What are you using for a disconnect for the compressor?
 
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Old 08-16-07, 07:55 AM
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Bob,

I want to put in a disconnect switch/junction box next to the compressor. I'm thinking of a 50amp disconnect like I had with an old hot tub setup, it had a bar that you could pull out and switch around to break the connection, it complied with county code.

But, I can't seem to find anything like that or anything at Home Depot or Lowes that will work. I'm going to have to go to a real electrical store to get a disconnect switch that will work.

BTW, The panel is only a few steps from the compressor.

Jimmee
 
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Old 08-16-07, 07:59 AM
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You can use the circuit breaker as a disconnect as long as they are in sight of each other.

However, you do not want to use the circuit breaker as an on/off switch, unless the circuit breaker is designed as such.
 
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Old 08-16-07, 09:01 AM
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Smile

I am a novice in the electricians world but I would think you could use a Air Conditioning Condensing Unit disconnect. Fused or non-fused I suppose. Perhaps Bob will confirm. I buy them at the H.D once in a while for about 12 bucks as I recall.
 
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Old 05-03-08, 07:34 AM
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Jumping on to make sure I am clear

We have a similar compressor set up - three wires from the compressor (black, white, red) @ 220 / 15 amp (5hp). We are going to put the compressor about 3 feet from the garage circuit breaker box. We were going to use 12-3 Romex (Black, white, red and copper).

So I wanted to make sure I understand a couple of things. We were not going to wire a disconnect since we are right next to the breaker box. We were going to do direct connections within a junction box. No reason not to do this, is there?

And so the wiring would go: Black and Red off 20 amp breaker to connect to black and red off of compressor. White to busser bar and capped in junction box. Copper to ground in circuit breaker box to white off of compressor? Is this correct?
 
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Old 05-03-08, 07:55 PM
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That close, if the compressor has no on/off control, you should have a disconnect you can use as a switch. Otherwise you are fine.
 
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