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Discussion Starter #1 (Edited)
I am attempting to install a 60 gallon, 3.2 hp, 240 volt Craftsman air compressor into my attached garage. I am trying to run a 240 volt circuit from the house breaker box located on the back wall of the house about 50 feet away from the garage. My plan is to run the circuit through the attic and into the garage to a 240 volt outlet (compressor will be plug in). What gauge wire do I need to use? I have a 100 foot 10 AWG heavy duty extension cord. It is flame, water and oil resistant. Can i cut to length and use this to wire the compressor? Do I need to use any conduit? Do I need any kind of a disconnect switch? I am in California if this matters.
Thank you in advance.
 

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I have a 100 foot 10 AWG heavy duty extension cord. It is flame, water and oil resistant. Can i cut to length and use this to wire the compressor? Do I need to use any conduit? Do I need any kind of a disconnect switch?
Thank you in advance.
Don't run extension cords in attic.Why not do it right and run a 60 Amp Circuit or 100 amp To a Sub Panel into the attached garage..:yes: Then you Will be able to add what you want( Lights, Receps). You don't need a disco for air compressor if it plugs in .
 

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Discussion Starter #3
Thank you for the reply. I already have lights and such in the garage. I just wanted to wire one 240 outlet for the compressor and I don't really see adding anything else in the near future. I was asking about the extension cord because I have it. I thought I could use it instead of buying bulk wire from a spool or Romex if 10 gauge was acceptable for this setup. My thinking is that the difference between the extension cord and bulk wire is the connectors on the ends of the extension cord. If they are removed then they are basically the same thing, right? If this is not ok I will buy the correct wiring. I just need to know what size, and should I use conduit? Thanks again.
 

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Thats right, no ext. cords in permanent applications. Sorry you just cannot do it.
You need a minimum of a 30 amp circuit for this motor. The FLA (amps) are around 17. (17 X 1.75) = 29.75. So a 30 amp double pole breaker and #10 wire is what you will need. Does the compressor have a plug on it? If it does it should be rated at 30 amp/250 volt. Is this what you have?
Run the cable (NM) 10/3 or 10/2 from the panel to a junction box. (You can use 10/2 or 10/3). I would run 10/3 regardless. Install a receptacle that matches the plug you have on the compressor. If the compressor does not have a factory installed cord and plug, let us know.

Note. 10/3 will leave you with one extra wire. Just put a wirenut on it and tuck it into the box.
 

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Discussion Starter #5
Thank you for clearing some things up. It does not have a factory installed plug.
What is the benefit of using 10/3 if the extra wire is not used? Is this for later upgrading? Thanks.
 

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10-3 For future so you will have a neutral wire (Price not much different) If it does not have a plug I would put a 220 switch close to the compressor.
 

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Thats right, no ext. cords in permanent applications. Sorry you just cannot do it....
No argument here. Extension cords are not to be used as permanent wiring.

...You need a minimum of a 30 amp circuit for this motor. The FLA (amps) are around 17. (17 X 1.75) = 29.75. So a 30 amp double pole breaker and #10 wire is what you will need....
Where are you getting this information from? I agree with the FLA being around 17, but this means that the circuit for this unit could be wired with a 12-2 cable. It also means that a singe NEMA 6-20R receptacle could be used as the required disconnect.

It also means he could use a 30 or even a 40 Amp breaker on that #12 wire.

12-2 wire is a LOT cheaper than 10-2 or 10-3. No need to spend the extra $$$ for unneeded capacity here.

I would ask the OP to clarify the rating of this compressor: Can you give us the specific information as shown on the nameplate of the unit?

Please post the following and let us know if the item is listed but left blank:

HP rating
Amps
Volts
 

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Discussion Starter #9
Ok. I capiche on the extension cord deal. Yes, that is my compressor.

3.2 hp
15 amp minimum
240 volt single phase

So, should I use 10 or 12 gauge?

That is the first time I have seen the bit about hard wiring it. I looked all through the owner's manual for something about wiring a cord but never found anything.

Once again thank you for all of your input.
 

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While 12-2 would be acceptable, I guess I don't like the idea of protecting it at 30 A. I would run 10-2 from a 30 A breaker to a 60 amp A/C disconnect, and whip out to the compressor with seal tite.
 

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While 12-2 would be acceptable, I guess I don't like the idea of protecting it at 30 A. I would run 10-2 from a 30 A breaker to a 60 amp A/C disconnect, and whip out to the compressor with seal tite.
Note that the manufacturer's specs say "15A minimum" - which doesn't jive with the HP rating. Most consumer-market air compressors are given HP "ratings" that are grossly inflated and have almost nothing to do with the actual HP output of the motor during operation. You have to go by the nameplate current to get an idea of the actual requirements. It says 15A, and that can be believed - a 20A breaker on #12 wire should be more than sufficient.

Campbell-Hausfeld got sued in a class action for this a few years back, since they were apparently just picking random impressive numbers for their HP ratings. They agreed to stop, and now rate their compressors using an unrealistic HP number that is still not in compliance with industry standard measurement practices, but has some basis in testing. It's like the peak power produced by the motor immediately before stalling, or something.
 

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Ok. I capiche on the extension cord deal. Yes, that is my compressor.

3.2 hp
15 amp minimum
240 volt single phase

So, should I use 10 or 12 gauge?

That is the first time I have seen the bit about hard wiring it. I looked all through the owner's manual for something about wiring a cord but never found anything.

Once again thank you for all of your input.
12-2 is more than adequate in this case. As someone else pointed out, those HP ratings may be inflated a bit, since some manufacturers want to make it look like their compressors are more than they are. Is that HP rating on the motor itself, or posted elsewhere on the unit? Look at the nameplate on the actual motor. Betcha a dollar to a donut the HP rating is blank .... :furious:
 

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Discussion Starter #13
The nameplate actually says '3.2 hp Tested per ISO 1217', whatever that means. The nameplate also reads 13 amps.
 

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The nameplate actually says '3.2 hp Tested per ISO 1217', whatever that means. The nameplate also reads 13 amps.
With a 13 amp load, you woould need 12/2 and a 20 amp circuit. I don't see how they can list a 15 amp circuit min.
 

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With a 13 amp load, you woould need 12/2 and a 20 amp circuit. I don't see how they can list a 15 amp circuit min.
If it draws 13 A, then I would use a 20 A circuit. But then again, I have seen some compressors struggle to start and pop a 20 A breaker. I might still run a 25 or 30 A circuit. I'd just have to be there, I guess.
 

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If I were installing this compressor at my house, or installing it at your house as an employee of an electrical contractor, I'd install a 30 amp breaker in the panel, then use a 12/2 from the panel to a disconnect of some sort, then either cord or flex from the disconnect to the compressor.

If I were advising you to install it, do the same thing except use 10/2.

The reason is because I know the code well enough to legally justify my installation. I've 'educated' (tactfully) several inspectors over the years.

Unless you know the code well, it's better to grossly overkill the installation so as to not raise eyebrows.

Rob.
 

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What some are missing here is starting current. Compressors are notoriously under protected and tripping of the OCPD (circuit breaker) is the result. When sizing a breaker or fuse for a motor you must consider this in the calculation. FLA x 1.75 = 29.75. This is the value you MUST use to size the OCPD and wire*. Since they do not make a 29.75 amp breaker, you need a 30 amp breaker. While you may legally install #12 wire on this 30 amp circuit*, I would not do it. I would use #10 following NEC Art.310.16.

The OP will have no external overload to adjust, (unless the compressor comes with one, or he installs one himself) so the breaker is the only protection he will have. The 30 amp breaker will allow this compressor to start. The internal (non-adjustable) thermal overload in the motor will protect at (running current).

I agree with Rob and InPhase regarding the addition of the disconnect and the subsequent wiring after the disco. In this application we are addressing a significant motor load. You cannot just look at the name plate and size the OCPD and wire to this value. I would be willing to bet, if you put this motor (17 amp) on a 20 amp breaker and push the start button the OCPD (breaker) would trip instantly. It will not work, period.

*The NEC has exceptions for wire sized smaller than allowed in Art.310.16. For the sake of not confusing the OP we can save this for another discussion.

Note: Yes 10/3 for future expansion.
 

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What some are missing here is starting current. Compressors are notoriously under protected and tripping of the OCPD (circuit breaker) is the result. When sizing a breaker or fuse for a motor you must consider this in the calculation. FLA x 1.75 = 29.75. This is the value you MUST use to size the OCPD and wire*. Since they do not make a 25 amp breaker or a 29.75 amp breaker, you need a 30 amp breaker. While you may legally install #12 wire on this 30 amp circuit*, I would not do it. I would use #10 following NEC Art.310.16.

The OP will have no external overload to adjust, (unless the compressor comes with one, or he installs one himself) so the breaker is the only protection he will have. The 30 amp breaker will allow this compressor to start. The internal (non-adjustable) thermal overload in the motor will protect at (running current).

I agree with Rob regarding the addition of the disconnect and the subsequent wiring after the disco. In this application we are addressing a significant motor load. You cannot just look at the name plate and size the OCPD and wire to this value. I would be willing to bet, if you put this motor (17 amp) on a 20 amp breaker and push the start button the OCPD (breaker) would trip instantly. It will not work, period.

*The NEC has exceptions for wire sized smaller than allowed in Art.310.16. For the sake of not confusing the OP we can save this for another discussion.

Note: Yes 10/3 for future expansion.
I figured the "15A Minimum" statement on the nameplate was referring to the circuit ampacity, not the FLA rating of the motor. If it were the FLA rating, then your calculation would of course be correct - but these consumer compressors rarely state FLA, they state the required circuit ampacity. If the "15A Minimum" does refer to the OCPD and not FLA rating, then a 30A breaker on #12 wire would not be permissible in this application, would it?
 

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On a 30 AMP Why risk a possible fire?!? Run new 10/3 or 10/2 copper (which is rated for 30 Amps) and be done with it. Physics is physics.. try to pull too much current through a piece of copper wire and it WILL overheat and possibly burn.
 

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I figured the "15A Minimum" statement on the nameplate was referring to the circuit ampacity, not the FLA rating of the motor. If it were the FLA rating, then your calculation would of course be correct - but these consumer compressors rarely state FLA, they state the required circuit ampacity. If the "15A Minimum" does refer to the OCPD and not FLA rating, then a 30A breaker on #12 wire would not be permissible in this application, would it?
No. The circuit ampacity includes the motor.
I went to the link someone posted and you verified it was your compressor, but saw no electrical specs at all. It only said that it must be installed by a qualified electrician. So I have no idea where this 15 amp min. comes from. You need to know what the full load amps are. The whole unit (amps) are fine. Call them if you have too. It's Sears right? They will discuss this with you, I would hope.

I just located NEC Table 430.52. It actually requires a multiplier of 2.50 for an inverse time breaker. Thats whats in your panel. These are maximum values, not minimum. So, just go with 2.50 x (amps) all around and you should be just fine. (Breaker and Wire)
Still contact the manufacturer and make sure they agree.
 
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