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reduced cable

MrJack96
Hi guys just wanted to ask what you think of this. 


there is a bit of temporary kit which runs a 22KW motor. the FLC is 41 amps the cable supplying the motor is 10mm flex this then goes into a JB which someone has connected 6mm YY cable (4 core Lapp 130H) to extend the cable to a local isolater. the local isolator where the supply has been picked up from is a 100amp supply fed from a MCC approx 50 meters away. the method of starting is by soft start. 


I spoke to another Electrician who told me its fine as it is as the overload has been switched down. my thoughts were the overload protects the motor not the cable. I know the maximum capacity of the cable is 44amps so i can understand the overload should trip but is there an issue just relying on the overload. my suggestion was to down rate the fuses after the soft start to 40amps  i know its close but for a temporary measure, the motor runs at 32 amps normally.
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    is there an issue just relying on the overload

    Not really - it's common in industrial motor circuits for the circuit protection to provide only fault protection and thus to be rated significantly higher than the cables they protect. That way when the motor overloads (commonly due to mechanical overload) it's the local overload that trips rather than the remote circuit protection. In the days of fuses there were even specific "motor" fuses that had a higher rating than their size would normally indicate - so in effect you could put something like a 30A fuse in a 20A holder.

       - Andy.
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  • 0
    is there an issue just relying on the overload

    Not really - it's common in industrial motor circuits for the circuit protection to provide only fault protection and thus to be rated significantly higher than the cables they protect. That way when the motor overloads (commonly due to mechanical overload) it's the local overload that trips rather than the remote circuit protection. In the days of fuses there were even specific "motor" fuses that had a higher rating than their size would normally indicate - so in effect you could put something like a 30A fuse in a 20A holder.

       - Andy.
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