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Cable routing/eddy currentso

Baldyhugh
Hi


I have a query regarding a cable route for  a job I’m currently on (when lockdown rules allow me back to it!). I have to supply a feed motor on a farm, the contactor feeding it is at one end of the building in a plant room. There is an existing steel trunking running the length of the building and I plan to come out of this close to the motor with pvc conduit. However there is a paddle switch in the meal hopper beside the motor that will control the contactor. This needs a simple two wire connection. My question is can I run these two cables out of the trunking in the same conduit as the cables to the motor. I plan to put a wiska box or similar at the other end of the conduit so that I can split off to the motor and paddle switch separately, and there will be an isolator before the motor. 

The question however remains regarding the ‘control cables’ in the same conduit as the motor supply. They are from the same circuit and the same voltage but was concerned about eddy currents. 

Thanks in advance
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    Yes that is correct. If all cables run through the same hole the magnetic effects will be zero so no large heating can occur in the steel trunking. In practice though the heating effect would be pretty small as the load is pretty small, and the coil paddle switch current is tiny, so any heating effect will be negligible. BUT to comply with B.S. 7671 all load carrying cables should definitely run through the same hole.


    Is the supply earthing TT as it is a farm? Are there animals about?


    Z.
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  • 0
    Yes that is correct. If all cables run through the same hole the magnetic effects will be zero so no large heating can occur in the steel trunking. In practice though the heating effect would be pretty small as the load is pretty small, and the coil paddle switch current is tiny, so any heating effect will be negligible. BUT to comply with B.S. 7671 all load carrying cables should definitely run through the same hole.


    Is the supply earthing TT as it is a farm? Are there animals about?


    Z.
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