11 Kw 380 volt motor tripping 80 amps automatic fuse, what to search for?
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    Default 11 Kw 380 volt motor tripping 80 amps automatic fuse, what to search for?

    yesterday the screw compressor had to be serviced and it was found the bearing of the cooling vent was shot.
    the service tech just said there no longer were parts available and left.
    the identical spare compressor was pressed into service but tripped the 30 amp automatic 3 phase fuse block as well as one 80 amp main fuse as soon as the compressor was powered up.
    there are three main fuses each serving one phase.
    it was possible to get it going if all other electrical devices were shut off before attempting to start up the compressor.
    all other electrical devices in this case means some lighting, some computers but no major other electrical devices.
    both compressors are identical and have a 11 Kw 380 volt motor.
    the spare compressor turns readily by hand just like the other one.

    the fact that only one main 80 amp fuse trips, makes me think there could be an internal short in one of the windings of the motor.
    the 30 amp 3 phase automatic fuse cuts all three phases if only ones trips.

    any ideas about things i could check before getting the motor out and having it checked?

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    Did you check rotation ?

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    Yesterday I was called to a place, A 15 HP motor was tripping a 100 Amp breaker, problem was a bad connection.

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    i take it to be okay as the compressor used to work before and nothing needed to be changed, but i will check anyway.

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    i will have them check the connections

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    Quote Originally Posted by digger doug View Post
    Did you check rotation ?
    i rotated the input shaft by hand in both directions, it felt the same smooth rather effortless rotation on both compressors.
    as one was, apart from the cooling fan, working okay, i assumed the other one to not have a problem in that regard.

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    Quote Originally Posted by janvanruth View Post
    i rotated the input shaft by hand in both directions, it felt the same smooth rather effortless rotation on both compressors.
    as one was, apart from the cooling fan, working okay, i assumed the other one to not have a problem in that regard.
    NO

    When hooking up 3 phase, you "bump" the contactor (on and then off quickly)
    to CHECK which way the motor is rotating. You don't want it to come up to speed.

    Unlike single phase, reversing a 3 phase motor does not involve removing any covers from the motor.
    Last edited by digger doug; 02-21-2020 at 05:06 PM.

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    Quote Originally Posted by digger doug View Post
    NO !

    When hooking up 3 phase, you "bump" the contactor (on and then off quickly)
    to CHECK which way the motor is rotating. You don't want it to come up to speed.

    Unlike single phase, reversing a 3 phase motor does not involve removing any covers from the motor.
    now i see what you mean, i thought i was supposed to rotate it to see if it were seized.
    the spare compressor has had some working time in the past and is connected by a standard plug to a wall outlet.
    in order to shift from main to spare compressor the compressor is unplugged and the other is plugged in.
    so there is not much chance of having the compressor rotate the wrong direction.
    but as the repair on the cooling shaft of the main compressor is working and the main is on line again i will check if the direction of rotation is the same for both.

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    Quote Originally Posted by janvanruth View Post
    the spare compressor has had some working time in the past and is connected by a standard plug to a wall outlet.
    in order to shift from main to spare compressor the compressor is unplugged and the other is plugged in.
    so there is not much chance of having the compressor rotate the wrong direction.
    Surely there IS. All it would take is for a "different' outlet to have had its Phases arranged differently - "proper" or not - and some prior technoid correcting that to match in the cord termination of the "other" compressor, "on machine".

    And then you move it to another outlet.

    Or NOT a problem. Probably is not.

    But this does happen, "out in the world", and not a lot of compressors are "don't care" as to direction of rotation. So is what Doug was suggesting at least be CHECKED for.

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    Quote Originally Posted by thermite View Post


    But this does happen, "out in the world", and not a lot of compressors are "don't care" as to direction of rotation.
    Yup.... I'll bet a screw compressor does care....would be like a Deetroit
    running backwards.

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    Quote Originally Posted by digger doug View Post
    Yup.... I'll bet a screw compressor does care....would be like a Deetroit
    running backwards.
    Rude-buggers ARE a tad quieter - if you can but convince them to keep at it!



    "Detroit", the city, OTOH, seems to have deliberately "run backwards" for easily 40 years.

    More to the OP's situation.. am I correct in re-translating:

    "automatic fuse" to "three-pole common-trip circuit breaker",

    AND

    Expecting it to require manual reset, AND NOT be of the tribe that self-reset after a time-out or cool-down?

    Not that I'd expect such a critter, 3-Phase machine tool supply service.

    But they made very good sense, cigar/cigarette lighter sockets, 1956 DeSoto et al, and a great many MORE motors subject to abuse, garbidge disposals to HVAC...

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    Quote Originally Posted by thermite View Post
    Rude-buggers ARE a tad quieter - if you can but convince them to keep at it!



    "Detroit", the city, OTOH, seems to have deliberately "run backwards" for easily 40 years.

    More to the OP's situation.. am I correct in re-translating:

    "automatic fuse" to "three-pole common-trip circuit breaker",

    AND

    Expecting it to require manual reset, AND NOT be of the tribe that self-reset after a time-out or cool-down?

    Not that I'd expect such a critter, 3-Phase machine tool supply service.

    But they made very good sense, cigar/cigarette lighter sockets, 1956 DeSoto et al, and a great many MORE motors subject to abuse, garbidge disposals to HVAC...
    indeed a three-pole common-trip circuit breaker that needs a manual reset.
    there is only one outlet for both compressors, so it is, plug out one, plug in the other.

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    Quote Originally Posted by janvanruth View Post
    indeed a three-pole common-trip circuit breaker that needs a manual reset.
    there is only one outlet for both compressors, so it is, plug out one, plug in the other.
    Wouldn't take a great deal of time to thoroughly check the cordset, plug, compressor-end terminations.

    There have been a couple of "mystery" trip-outs - recently - on PM where something had gone amiss and was overlooked because "it had been working fine...".


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