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Electric motor overheating

  1. Nov 15, 2013 #1
    Hello, looking for some information on electric motor theory for a problem I encountered on a friends machine. An on site generator is our power supply, our motor requires 480v/ac 3phase, our generator is providing 500v/ac but we are losing 30 volts under load from our extension leads. our motor is running very hot but not tripping overload relays. My question is - could the 30 volt loss of power cause this problem. Also if I increase the voltage output on my generator will it solve the problem. Thanks joe
  2. jcsd
  3. Nov 15, 2013 #2


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    Without knowing how the overload relays are sized, the mechanical load and current drawn by the motor vs. the nameplate max current it is hard to recommend anything. Accepting 30 volts of loss in the wiring is not exactly good practice even if it does put the voltage at the motor right where you want it. Also, 'very hot' is a relative term. It can depend on if the motor is ventilated in the way that the designers intended.
  4. Nov 15, 2013 #3


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    Is it possible the motor has a problem? If so, maybe that's where the 30 volt drop is coming from.
  5. Nov 16, 2013 #4
    Presuming the overload protection is suitable set on then the current it is in its correct limits. Elevated voltage could raise the no-load current-this could be checked of course. Usually the rated voltage is 460 V so 500 V [if this is the measured voltage at motor terminals] but 8.7% more it is not so elevated voltage.
    The motor could be “very hot” if the insulation permits this. Insulation class H permits a conductor temperature of 180 dgr.C and 70-80 dgr.C outside stator surface could be permissible.
    However the overload protection does not “protect” the motor against a defective ventilation or if a heat source in vicinity may deliver a substantial heat –even sunshine or else.
  6. Nov 17, 2013 #5


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    Hi Joe P. http://img96.imageshack.us/img96/5725/red5e5etimes5e5e45e5e25.gif [Broken]

    Check that the generator is matched to the motor's frequency, e.g., both 60Hz.
    Last edited by a moderator: May 6, 2017
  7. Nov 17, 2013 #6
    Thank you for the the helpful info, We are going to take more readings and check the motor tag specifications,
    Thanks all Joe
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