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reduced cable

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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  • Firstly can we confirm you mean 3 phase at 400V phase to phase I presume you probably do, as from your figures (at 30A *3 *230 is ~ 21000) 

    So is your concern that the 100 amp protection is a bit coarse for the cable, or that the motor may catch fire if overloaded with nothing tripping, or that the Zs will be too high ?

    It  rather depends how serious it would be if say the cable or motor got cooked and how the starter handles overloads.

    Mike.



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  • Firstly can we confirm you mean 3 phase at 400V phase to phase I presume you probably do, as from your figures (at 30A *3 *230 is ~ 21000) 

    So is your concern that the 100 amp protection is a bit coarse for the cable, or that the motor may catch fire if overloaded with nothing tripping, or that the Zs will be too high ?

    It  rather depends how serious it would be if say the cable or motor got cooked and how the starter handles overloads.

    Mike.



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