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  1. #1
    Join Date
    May 2005
    Posts
    1,349

    3 year old copeland scroll grounded..

    all 3 terminals..this is a 3 phase system

    ill check for acid but what causes all 3 to ground out?

    this is a walkin refer with 3 evaporators..customer says
    last evaporator never really put out cold air..

    thoughts?

  2. #2
    Join Date
    Feb 2009
    Location
    Tallahassee, FL
    Posts
    6,039
    Single phrasing can. Recommend a phase monitor and of course check for any problems once you have it running again.

  3. #3
    Join Date
    Oct 2004
    Location
    Central WA
    Posts
    1,509
    Name:  goodwinding.jpg
Views: 335
Size:  32.8 KB

    Obviously not your compressor but just a stock photo of a 3 phase stator. Notice how everything touches? A little fire on one winding will burn across everything and can short out the whole fam damly.

  4. #4
    Join Date
    May 2005
    Posts
    1,349
    O-tay..thanks..im not familure with a phase monitor..how do they work?

  5. #5
    Join Date
    Aug 2010
    Posts
    2,681
    Quote Originally Posted by primmers View Post
    all 3 terminals..this is a 3 phase system

    ill check for acid but what causes all 3 to ground out?

    this is a walkin refer with 3 evaporators..customer says
    last evaporator never really put out cold air..

    thoughts?
    How big is the motor? Any multi-hp will have a winding resistance that's close to "zero" as far as you can read on a normal multimeter.

    Motors are either wound as delta(Δ)or wye(Y). In Delta wound, all three corners are connected to outside. In "Y" the three ends are, but the center knot is not.

    As you can visualize, if any part of the winding touches the core, it will look like all 3 points are shorted, but in reality, you probably have a spot or two inside that shorted to the core.

    More difficult ones are partial shorts that cause some turns to be skipped, therefore cause abnormal phase imbalance (i.e. coil #1 with 20% of turns bypassed due to a short will have overcurrent)

  6. #6
    Join Date
    Mar 2009
    Location
    Mid-Mo
    Posts
    3,595
    Quote Originally Posted by primmers View Post
    O-tay..thanks..im not familure with a phase monitor..how do they work?
    It's an electronic device that monitors incoming voltages and watches for proper phasing. If voltage increases/drops or if it sees a voltage imbalance, it opens a set of contacts and shuts the machine down. Usually there is a built in time delay that is also configurable. If for some reason there is a power event where it has single phased, the monitor will hold it out until it sees good power again or you come reset it. The ones we use have a line/load feature where it watches the load side also.

  7. #7
    Join Date
    Aug 2012
    Posts
    2,650
    I think a phase monitor should be installed on all three phase motors, that would cause less failure in the field. Any thoughts?

  8. #8
    Join Date
    May 2005
    Posts
    1,349
    this system has one...and no acid in the sytem...BUT when i was packing up my tools one of the maintenance guys said he replaced a contactor some time ago, said one wire was burnt..............

  9. #9
    Join Date
    Sep 2002
    Location
    Virginia
    Posts
    3,164
    Quote Originally Posted by primmers View Post
    this system has one...and no acid in the sytem...BUT when i was packing up my tools one of the maintenance guys said he replaced a contactor some time ago, said one wire was burnt..............
    sounds like a wire was not tight on old contactor ... thats probly what began to fry the field wires

  10. #10
    Join Date
    May 2005
    Posts
    1,349
    thats what im thinking too^^^ glad the guy finally said something..

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