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Newbie; 3 phase, 460V, 12 wire motor; what if wrong hook up?

Discussion in 'General Electronics Discussion' started by BBN75, Oct 21, 2018.

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  1. BBN75

    BBN75

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    Oct 21, 2018
    Hello! I realize this is more of an electronic forum but I've looked all over trying to find an answer to what a motor would do if hooked up wrong. Hopefully some of the experts here know the answer as it's driving me crazy! This is for a motor on a fire suppression water pump at a large industrial plant. This was a complete system upgrade. I'm 99.9% sure I hooked this motor up as the attached 460//380V diagram shows. It's a 12 lead motor with the 4-7, 5-8, and 6-9 winding hookup and the L1-T1-T12, L2-T2-T10, and L3-T3-T11 motor lead connections. The motor was checked for proper rotation and I was told that it was correct. I wasn't present when this was done so I don't know if it barely turned or if it turned freely for a little while. It's in a very noisy environment and it wasn't noticed if the enclosed breaker did or didn't trip. A few days later, water was sent through the attached pump and the breaker kept tripping. I was told the hook up was looked at and it was hooked as L1-T1-T2, L2-T10-T12, and L3-T3-T11 connections. My question is; Would this have been a direct short with an accompanying BOOM if L1-T1-T2 and L2-T10-t12 connections were improperly did this way? Or, would the motor have even turned at all? Just curious as to what the motor reaction would have been if the wrong connections were made this way. I'm an industrial electrician with 29 years experience. Any and all input is greatly appreciated!
     

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  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Short L1 and L2 and blow the breaker - clearly wrong.
     
    BBN75 likes this.
  3. Minder

    Minder

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    657
    Apr 24, 2015
    You can draw out the Delta connections for each set of windings to see the result.
    It is wound double delta But as mentioned, if L1 L2 phases were shorted it did not even get chance to turn before it blew the breaker,
    How come it was hooked up wrong, it is plain enough on the plate?
    M.
     
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  4. BBN75

    BBN75

    2
    0
    Oct 21, 2018
    Thanks for the replies! L1 AND L2, which are 2 of the 3 wires bringing voltage to the motor, were NOT hooked together. I know there would have been a major melt down if any of those 3 wires were hooked directly together! The internal wires attached to the motor in the weatherhead, T1 and T2, were supposedly attached to L1. The other internal set of wires attached to the motor in the weatherhead, T10 and T12 were also supposedly attached to L2. I'm trying to find out what the motor reaction would have been if the internal wiring leads T1 and T2 had been hooked up as I was told they were. I've hooked several motors up over the years like this and I'm as close to positive that I can be that this one was hooked up properly. It's the internal motor hookups that the mix up supposedly happened in. As mentioned this was a complete upgrade and maybe something else was actually wrong? Just for clarification, the wires coming to feed the motor are sometimes called T leads by some and L or Line leads, by others. In this instance the L numbers are the ones coming to feed the motor. This is based on the nameplate of the motor calling them as the L wires and the motor internal wires as T wires. I call the wires coming to the motor T leads. I tried to present my original question using the nameplate designations. Hopefully this makes my question a little clearer. The answer I'm trying for is what would have happened if it were hooked up the way I was told it was? It just occurred to me that I may be trying to over analyze the replies. Are you both saying that if the hookup was incorrectly wired like I listed above, that it would have been the same as directly hooking 2 of the 3 wires coming to feed the motor?
     
  5. Minder

    Minder

    3,076
    657
    Apr 24, 2015
    Either way it was wrong!
    The hook up seems clear to me, why was it not hooked up the way the plate shows?
    Fortunately It most likely did no damage to the motor if the breaker tripped almost right away.
    The motor wingdings are two sets of Delta windings, either in series or parallel.
    Did the motor run when connected according to the diagram?
    M.
     
  6. Tha fios agaibh

    Tha fios agaibh

    2,152
    725
    Aug 11, 2014
    No. Not a direct short, just one phase fighting the other two.
    Usually a motor miswiring would blow the overcurrent protection right away, but since this is a fire pump (protected at about 600% of motor full load current) it likely did spin with an accompanying loud humming noise.
    You're right in your original notion of how it's wired: L1 hooked to T1,T12 L2 hooked to T2,T10 and L3 hooked to T3,T11.

    Transposing T2 and T12 wouldn't cause a direct short. Phases evenly loaded but still obviously not good for the motor.

    Its not hard to accidentally mistake a 2 for a 12 on the wiring. Thankfully it wasn't a dead short because that could have gone very badly.

    I would megger it out to verify the insulation wasn't compromised and check currents are balanced.
     
    Bluejets likes this.
  7. Bluejets

    Bluejets

    4,750
    999
    Oct 5, 2014
    Very lucky it didn't end badly.

    Reason why we were always taught L1,L2,L3, A1,B1,C1, C2,A2,B2.(or ABC, CAB)
     
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