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Thread: A/C compressor

  1. #1
    Join Date
    Sep 2007
    Posts
    177

    Default A/C compressor

    I need to move my outdoor AC compressor unit. When I started looking into how it is wired I found some things that puzzled me. I was hoping someone with more experience could set me straight.

    The line from the main breaker panel is aluminum 230V single phase, 2 pole on a 50 amp dual pole breaker. The line runs ~ 40 feet into a load box where it switches over to copper. That box has a 40 amp two pole breaker. The copper line runs outside to Square D box that has something that looks like a single pole breaker...but there is no amp rating on the switch. This leads out to a fairly new (4 years old) compressor which I believe uses something that looks like 14 gauge wire (or maybe even lighter) for a screw compressor. It seems to me the amount of power supplied to this unit is way over board for what is needed.

    So here are my questions.

    1. Do the second and third breakers/switches need to be there? What is the rationale (if any) for them being there?
    2. As I am moving the compressor, can I install a junction box inside, switch over to copper at the correct gauge for the compressor and put in a lower rated breaker at the main panel?
    3. I am moving the compressor away from the house so there will be no nearby surface to mount anything. Is this OK (to not have a switch box near the compressor) or do I need to put in a post near the compressor for mounting that external switch box?

    Thank you for any help anyone can give.

    -Walt

  2. #2
    Join Date
    Mar 2009
    Location
    wisconsin
    Posts
    159

    Default Re: A/C compressor

    well im not sure why the circuit is going to the second breaker box. The third one that you described is a local disconnect. Im guessing its an unfused one. You do need that disconnect within site of or within 25 feet of the compresor.

    with out all the compressor info its hard to tell what you need for wire size. 14 guage does seem small. unless it was sent with the unit itself, as if it were a factory set up

  3. #3
    Join Date
    Sep 2007
    Posts
    177

    Default Re: A/C compressor

    Regarding the switch box near the AC unit....does that box have to be visible from the AC unit? I could mount the switch box inside the house that would be within 25 feet.

    If the box does need to be visible from the AC unit, how is the box typically mounted when the unit is away from a wall? I was thinking of running conduit to the unit to get the freon lines out from the house. I was hoping to run the electrical lines in the same conduit. The idea was that the conduit would pop out of the ground near the unit and the line would run into the unit. Would a PT post positioned nearby provide an adequate means to mount the switch box (assuming it is all watertight)?

  4. #4
    Join Date
    Aug 2007
    Posts
    6,486

    Default Re: A/C compressor

    My local codes require that there be a disconnect at the unit itself. Heck, our AC is right next to the main panel and there is STILL a disconnect on the wall behind the AC unit. Odds are your local code requires the same disconnect be within 3' or 4' of the unit.

    As for having to run through sub-panels, how you power up the unit from your main is up to you. All the installations I've ever seen have been fed directly from the main panel. If you've got sub-panels, it's possible that your main is not rated for the load OR it was an afterthought and added later with other electrical needs.

    I know you like to do stuff yourself, but if it were me, I'd consult with a local electrician. At the very least, check with your building department to see what is required in your area.

    BTW, good to see you again Walt. We miss not having you around.
    I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!

  5. #5
    Join Date
    Mar 2009
    Location
    wisconsin
    Posts
    159

    Default Re: A/C compressor

    Yes the disconnect needs to be within site of the unit. the whole idea is safety for who ever would happen to be working on it. Someone could go flip the breaker on while your working on it, and you would never know.

    Id mount the disconnect right to the unit itself if it was me. then just chase through it.

  6. #6
    Join Date
    Aug 2011
    Posts
    37

    Default Re: A/C compressor

    The A/C unit will have a label stating the minimum ampacity of the wire required and the maximum ampacity for the circuit breaker.

  7. #7
    Join Date
    Jan 2011
    Location
    Columbiana, Alabama
    Posts
    623

    Default Re: A/C compressor

    Walt,think of the large first breaker in the main panel as the most unlikely place a breaker on that circuit will trip. It has to protect the wire on that circuit which feeds the next smaller breaker.

    The second breaker (smaller than the first) will most likely trip if the compressor draws too much current. Since it is smaller than the 1st breaker the wire it protects can also be smaller.

    The way you described the last "breaker" if you look at it closely it may say something like "does not provide overcurrent protection" so it is simply a disconnect, which is required within 25 ft of the compressor (and in-sight of it).

    All disconnects have to be within 25 ft of and in-sight of the their associated equipment.

    The only reason to have the 2nd breaker is to make it more convenient to reset.

    Most A/C units require Copper wire (CU) and the nameplate will state: the minmum breaker size and the maximum size, I usually use large enough wire to use the largest size breaker allowed.

    I too believe the #14 wire may be too small, if the compressor draws more than a constant 12A, and may actually cause the compressor to fail. But, the small, newer units actually state a 15A breaker is the max. allowed. Read the nameplate.

    Good Luck from Columbiana, Alabama
    Maurice Turgeon,http://thesemi-retiredelectrician.com

  8. #8
    Join Date
    Jun 2007
    Location
    Fayette County, Ohio
    Posts
    5,560

    Default Re: A/C compressor

    Is it possible that an older higher amperage unit was replaced and the second breaker was installed per the new requirements while leaving old wiring in place? You could mount a cut off switch on the unit itself if you can find a place that won't puncture the lines.

    Jack
    Be sure you live your life, because you are a long time dead.-Scottish Proverb

  9. #9
    Join Date
    Jan 2008
    Posts
    1,109

    Default Re: A/C compressor

    Service disconnects should never be mounted to the units they serve. This logic is simple- you'll have to deal with exposed hot wiring if you replace the unit- the very thing the disconnect box is supposed to prevent! Probably a low-level pole mounted disconnect box w/conduit next to the unit will meet code and look OK but always check. Codes change with time and vary by locale.

    Phil

  10. #10
    Join Date
    Aug 2011
    Posts
    37

    Default Re: A/C compressor

    Quote Originally Posted by The Semi-Retired Electric View Post
    Walt,think of the large first breaker in the main panel as the most unlikely place a breaker on that circuit will trip. It has to protect the wire on that circuit which feeds the next smaller breaker.

    The second breaker (smaller than the first) will most likely trip if the compressor draws too much current. Since it is smaller than the 1st breaker the wire it protects can also be smaller.

    The way you described the last "breaker" if you look at it closely it may say something like "does not provide overcurrent protection" so it is simply a disconnect, which is required within 25 ft of the compressor (and in-sight of it).

    All disconnects have to be within 25 ft of and in-sight of the their associated equipment.

    The only reason to have the 2nd breaker is to make it more convenient to reset.

    Most A/C units require Copper wire (CU) and the nameplate will state: the minmum breaker size and the maximum size, I usually use large enough wire to use the largest size breaker allowed.

    I too believe the #14 wire may be too small, if the compressor draws more than a constant 12A, and may actually cause the compressor to fail. But, the small, newer units actually state a 15A breaker is the max. allowed. Read the nameplate.

    Good Luck from Columbiana, Alabama
    Maurice Turgeon,http://thesemi-retiredelectrician.com
    Where can I find your documentation on your "25' " rule? Code article please.

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