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Old 04-25-2013, 10:44 PM   #1
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Wiring a new air compressor


Two questions, just bought an 80 gallon Kobalt air compressor from Lowes, 240V rated 18.5 amps.

The instructions didn't include a wiring diagram so I wasn't certain whether I'd need a neutral or not. I wanted to get all my material in one trip, so I bought 6-3 cable figuring extra wires is better than not enough. So, I don't need neutral at the air compressor. Should I connect the wire at the circuit breaker panel or leave the neutral folded up off to the side?

I sized the breaker and wire based on a 30A circuit, I assumed that a 20 amp circuit for a device using 18.5 A might have been undersized, was I correct?

I also have a disconnect beside the on off switch at the compressor.

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Old 04-25-2013, 10:53 PM   #2
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Originally Posted by WillK View Post
Two questions, just bought an 80 gallon Kobalt air compressor from Lowes, 240V rated 18.5 amps.

Cool ya got something to play with it.


The instructions didn't include a wiring diagram so I wasn't certain whether I'd need a neutral or not. I wanted to get all my material in one trip, so I bought 6-3 cable figuring extra wires is better than not enough. So, I don't need neutral at the air compressor. Should I connect the wire at the circuit breaker panel or leave the neutral folded up off to the side?

The straight 240 volt moteur what you have there you will not need the netural at all.

Ya can cap it off on both end but see the comment below on that question.

But why end up buy 6-3 cable ?? how far is the compressour is located from the main panel ??


I sized the breaker and wire based on a 30A circuit, I assumed that a 20 amp circuit for a device using 18.5 A might have been undersized, was I correct?

I also have a disconnect beside the on off switch at the compressor.
My reply in bleu.

Good move with disconnect switch that is my SOP with it unless you are in sight of breaker / fuse box.

Do this compressour do have thermal protection on the moteur or not ? ( that may change the way I will suggest the breaker size )

I know 20 amp breaker can hold it but normally I will sized by C.V.( HP ) and amps et voltage et distance so I know what I am dealing with it.

Merci,
Marc

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Old 04-26-2013, 07:28 AM   #3
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Wiring a new air compressor


Is this the unit?





If so, based on the specs found here the NEC requires the following;

FLA=28A
230VAC

BC conductors have to be 8/2 romex, or #10 THHN/THWN in conduit.
ITCB can be as high as 70A to allow for motor to start and run.

If the unit is not within site of the breaker panel, a disconnect will be needed. Use a non-fused knife switch which has to be horsepower rated. If a cord and plug is used it has to be horsepower rated. Which means you should hard wire the unit.

Finally, consult the manufaturers installation instructions for what they require.

Good luck!!
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Last edited by electures; 04-26-2013 at 08:43 AM.
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Old 04-26-2013, 09:23 AM   #4
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Pfft... I have no idea why I said 6-3, what I meant was that I have 10-3 NM.

I ran it inside 1/2" flex metal conduit where exposed. I bought a fused disconnect, and the air compressor is within 5 feet of the main panel. Overkill, but the way I see it I can use the hardware for when I'm remodelling the garage later.

And actually, mine is the 3 cylinder 80 gallon Kobalt compressor:
http://www.lowes.com/ProductDisplay?...llow&cId=PDIO1

Little bit lower current. I was wondering if I could've gotten away with a 20 amp rated circuit, but since 20 amps would have been marginal and I recall some parts of the code about not using 100% of the current rating, and not knowing whether that section applies to this installation, I thought it would be better to go up to the next gage and breaker size.
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Old 04-26-2013, 11:22 AM   #5
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Wiring a new air compressor


Don't know and highly doubt a 20 amp circuit would have been enough. Post the nameplate information. All of it.
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Old 04-26-2013, 05:44 PM   #6
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Quote:
Originally Posted by WillK
Pfft... I have no idea why I said 6-3, what I meant was that I have 10-3 NM.

I ran it inside 1/2" flex metal conduit where exposed. I bought a fused disconnect, and the air compressor is within 5 feet of the main panel. Overkill, but the way I see it I can use the hardware for when I'm remodelling the garage later.

And actually, mine is the 3 cylinder 80 gallon Kobalt compressor:
http://www.lowes.com/ProductDisplay?...llow&cId=PDIO1

Little bit lower current. I was wondering if I could've gotten away with a 20 amp rated circuit, but since 20 amps would have been marginal and I recall some parts of the code about not using 100% of the current rating, and not knowing whether that section applies to this installation, I thought it would be better to go up to the next gage and breaker size.
Follow the links in my signature for sizing motors. First rule. Do not use the nameplate rating. The NEC has to be used.
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Old 04-26-2013, 06:35 PM   #7
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Wiring a new air compressor


Quote:
Originally Posted by electures View Post
Follow the links in my signature for sizing motors. First rule. Do not use the nameplate rating. The NEC has to be used.
There you go again.
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Old 04-26-2013, 08:31 PM   #8
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Wiring a new air compressor


Quote:
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Follow the links in my signature for sizing motors. First rule. Do not use the nameplate rating. The NEC has to be used.
There's a strong argument that this is not a "motor", but an "air compressor" which has certain manufacturer-specified UL-approved ratings, listed on the ratings plate.
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Old 04-26-2013, 09:14 PM   #9
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Okay... so it sounds like I need to up the conductors to #8, and up the breaker to 40A... And the disconnect is under-rated since it's 30A, so probably easiest to just not use the disconnect. Is that right?
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Old 04-26-2013, 09:27 PM   #10
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Quote:
Originally Posted by WillK View Post
Okay... so it sounds like I need to up the conductors to #8, and up the breaker to 40A... And the disconnect is under-rated since it's 30A, so probably easiest to just not use the disconnect. Is that right?
You will be fine with 10 conductors and a 30 amp breaker.
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Old 04-26-2013, 11:02 PM   #11
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Quote:
Originally Posted by mpoulton

There's a strong argument that this is not a "motor", but an "air compressor" which has certain manufacturer-specified UL-approved ratings, listed on the ratings plate.
If that is the case then UL would have a separate standard for air compressors. Just like pool filter motors.

Edit: the UL standard for Air Compressors is UL 1450. Doesn't say anything special for motors.
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Last edited by electures; 04-26-2013 at 11:20 PM.
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Old 04-26-2013, 11:13 PM   #12
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Wiring a new air compressor


Quote:
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Follow the links in my signature for sizing motors. First rule. Do not use the nameplate rating. The NEC has to be used.
Normally I don't useally knock on your door on this one but according to the OP's specs the 4.7 CV ( HP ) is not a common number at all and for a fun part I try to plug the numbers for French codes which we do have IEC and NEMA format ( we don't use the NEMA very often but it is very handy to figures few items what the IEC don't cover ) and I read the specs sound like 2.5 CV moteur due the running current drawage which it did stated 18.5 amps @ 240 volts.

Do you have special chart for oddball moteurs ?

I did read the OP's moteur specs and good thing it did came with interal thermal overload protection.

Merci,
Marc
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Old 04-29-2013, 07:42 AM   #13
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There you go again.
My recommendations are based on the unit in my link. Since it is not the same unit, obviously since the motor is different the requirements will change. Never heard of a 4.7 HP motor. I'll have to visit a Lowes and check it out.

If anybody disagrees with my calculations, please feel free to prove me wrong and back it up with relevant documentation including NEC sections.
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Old 04-29-2013, 05:13 PM   #14
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Quote:
Originally Posted by electures View Post
My recommendations are based on the unit in my link. Since it is not the same unit, obviously since the motor is different the requirements will change. Never heard of a 4.7 HP motor. I'll have to visit a Lowes and check it out.

If anybody disagrees with my calculations, please feel free to prove me wrong and back it up with relevant documentation including NEC sections.
I've done that several times in the past and you refuse to relent from your assertion that all utilization equipment with motors must be sized from
NEC tables and it justis not true.
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Old 04-29-2013, 05:19 PM   #15
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Quote:
Originally Posted by brric View Post
I've done that several times in the past and you refuse to relent from your assertion that all utilization equipment with motors must be sized from
NEC tables and it justis not true.
What changes this fact? I want to hear both sides of the story.

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