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Thread: Three fuses

  1. #1
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    Three fuses

    What possible scenario could cause a loss of all three fuses? I replaced the fuses and found no problems.


    It was a 30 ton chiller with four compressors, the number one compressor in A stage was the one with the blown fuses.



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    Single phase

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    Single phase could occur if one fuse blew, causing the other two fuses to draw high current, but it's not normal for both hot TD fuses to fail the same instant. 3 bad fuses is usually a ground. Did you megger the motor and check wiring, connections, etc? More common on 480 volt systems.

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  6. #4
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    Quote Originally Posted by tunaguy View Post
    Single phase could occur if one fuse blew, causing the other two fuses to draw high current, but it's not normal for both hot TD fuses to fail the same instant. 3 bad fuses is usually a ground. Did you megger the motor and check wiring, connections, etc? More common on 480 volt systems.
    I have checked everything, and what's the odds that the two remaining time delay fuses blow at the time?

  7. #5
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    If they're drawing too much current, the odds are very high.
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    2 Tim 3:16-17

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  9. #6
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    Of course anytime a fuse blows you want to be checking the fuse holder. If you're talking about an ancient disconnect, the fuse holders have probably lost their tension on the fuse end caps, and if so, the disconnect should be replaced.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  10. #7
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    Quote Originally Posted by timebuilder View Post
    Of course anytime a fuse blows you want to be checking the fuse holder. If you're talking about an ancient disconnect, the fuse holders have probably lost their tension on the fuse end caps, and if so, the disconnect should be replaced.

    How often have you seen three fuses blow, without a trace of why?


    This unit has a phase monitor, the Carel records events and also has Carel current sensors for each compressor.

  11. #8
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    This can happen when the disconnect holders allow the fuses to overheat when the current is still normal.
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  13. #9
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    Quote Originally Posted by timebuilder View Post
    This can happen when the disconnect holders allow the fuses to overheat when the current is still normal.
    No discoloration anyplace on any thing, I spent nearly two hours going over it. Fuses are very tight in the holders, put a megger on the compressor, starter is new, power cable to the compressor is new.


  14. #10
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    Sounds like a pretty good mystery.

    It may not have a clear cause.
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    2 Tim 3:16-17

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  15. #11
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    Quote Originally Posted by timebuilder View Post
    Sounds like a pretty good mystery.

    It may not have a clear cause.
    Fuses, maybe they came from Shenzhen.

  16. #12
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    Never seen all 3 blow ... nope

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  18. #13
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    Everything seems to come from there.....
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