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  1. #1

    leibert 20 ton unit shorted to ground

    Hey all. I can't believe I'm asking this, but I just want to make sure. I have a Carlyle compressor in a Leibert 20 ton unit. Blown contactor and fuses. I've got correct Ohms between legs, but I also have Continuity to ground on each leg. I know this isn't right, but is it common to have a short to ground on every leg; Or am I missing something.

  2. #2
    Join Date
    Jul 2006
    Location
    Brooklyn , NY
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    24
    Quote Originally Posted by jim4237 View Post
    I know this isn't right, but is it common to have a short to ground on every leg; Or am I missing something.
    Yes, its common for 3 phase motor,
    if one leg short to ground other short too.


  3. #3
    Join Date
    Nov 2008
    Posts
    1,673
    Did the first leg to short cause the other two shorts?

  4. #4
    Join Date
    Jun 2008
    Location
    Apopka, Florida
    Posts
    110
    Quote Originally Posted by jim4237 View Post
    Hey all. I can't believe I'm asking this, but I just want to make sure. I have a Carlyle compressor in a Leibert 20 ton unit. Blown contactor and fuses. I've got correct Ohms between legs, but I also have Continuity to ground on each leg. I know this isn't right, but is it common to have a short to ground on every leg; Or am I missing something.
    Jim,

    When you say a blown contactor, What do you mean?

    I have seen many a circumsatnce that technicians do not change badly pitted contactors and then what to know why they lost a compressor. When it was obvious that the contacts welded together and ran the compressor into oblivion or unitil she just shot the bed. Because of a 30 dollar part the lost a 4000 dollar compressor, it just don't make sense.

    But it is common for the high voltage to short together, to ground, or too the internal overload which would cause more damage running high voltage thru the control circuits.

    Domcort

  5. #5
    Join Date
    May 2008
    Location
    Woodhaven, Michigan, United States
    Posts
    58
    yes it would be all three if melted contacts but im surprised there isnt any open windings then at least one

  6. #6

    short

    I was testing fire alarms and it shunt tripped the hvac units. After resetting breakers I noticed it was getting hot in space. The contactor on compressor 1 was fried; burnt wires, etc. I replaced contactor and fuses and restarted without checking motor. It blew all the fuses again immediately. Seems like L3 fuse was hotter than the other 2 legs. Isolated motor and OHM'd out each leg to ground and got resistance on each. And also got resistance between each leg.

  7. #7
    Join Date
    Jun 2008
    Location
    Apopka, Florida
    Posts
    110
    Quote Originally Posted by jim4237 View Post
    I was testing fire alarms and it shunt tripped the hvac units. After resetting breakers I noticed it was getting hot in space. The contactor on compressor 1 was fried; burnt wires, etc. I replaced contactor and fuses and restarted without checking motor. It blew all the fuses again immediately. Seems like L3 fuse was hotter than the other 2 legs. Isolated motor and OHM'd out each leg to ground and got resistance on each. And also got resistance between each leg.
    Jim,

    Burnt wiring, smybolizies that there may have been a loose connection(s).

    Anything can happen internally to the compressor, shorting phase to phase and then to ground can happen, shorting high voltage to the internal overload can also happen, which is low voltage.

    Looks like a replacement compressor is needed, if you have the original compressor rebuilt you may get a better understanding of whta happened internally.

    keep us posted,
    Domcort

  8. #8
    Join Date
    Nov 2008
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    1,673
    Quote Originally Posted by Domcort View Post
    Burnt wiring, smybolizies that there may have been a loose connection(s).
    if it's within a few inches of the connection. Crispy the whole length means overload.

  9. #9
    Join Date
    Jun 2008
    Location
    Apopka, Florida
    Posts
    110
    Quote Originally Posted by WhoIsThat? View Post
    if it's within a few inches of the connection. Crispy the whole length means overload.
    I would agree with that, the fuses protect the wiring and the device i.e, the load.

    Domcort

  10. #10
    Join Date
    Nov 2008
    Posts
    1,673
    20A through a bad connection having 0.02 Ω contact resistance is 8 W. If the connection has a small surface area [e.g., that of a pea] it will get very hot.

    I had a half volt drop @10A through a badly installed wirenut connection. I was pulling 10A to check for bad connections just like this one.

  11. #11
    Join Date
    Jan 2009
    Location
    Paradise, NL, Canada
    Posts
    41
    Disconnect the wires from the compressor terminals and check there to rule out an external wiring or contactor problem. I would bet the compressor is toast.

  12. #12
    Join Date
    Apr 2003
    Location
    the Great Pacific Northwest
    Posts
    607
    Quote Originally Posted by jim4237 View Post
    Hey all. I can't believe I'm asking this, but I just want to make sure. I have a Carlyle compressor in a Leibert 20 ton unit. Blown contactor and fuses. I've got correct Ohms between legs, but I also have Continuity to ground on each leg. I know this isn't right, but is it common to have a short to ground on every leg; Or am I missing something.
    Just to clarify, the short to ground is most likely or could be at just one location or area of on of the three independent windings of the motor. the motor windings are connected internally at each of the power connestions, if you were to designate the windings with letters as A,B,C, then terminal 1 would have the " input" lead of winding A and the "output" of winding C connected to it,terminal 2 would have the " input" lead of winding B and the "output" of winding A connected to it, terminal 3 would have the " input" lead of winding C and the "output" of winding B connected to it.

    Therefore, if the short to ground is anywhere in the motor you will read it on all three motor terminals.

    Hope this helps.

  13. #13
    Join Date
    Jan 2007
    Location
    Charm City--the city that bleeds
    Posts
    2,790
    when you say "continuity to ground", do you mean low resistance?
    Typically if your standard multimeter is ringing to ground then yes, it's gone. But, I'm just looking for you to clarify a bit.

    What are the values of each leg to ground?

    Are you talking like Megohms or are you talking 10, or 800, or 27K ohms?
    It's great to be alive and pumping oxygen!

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