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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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    If I run an earth cable to the switch from one of the lighting circuits, would I also need to run one from the other lighting circuit incase at some point later on the first lighting circuit is removed for some reason, leaving the other circuit live but with no earth at the switch?



    BS 7671 permits two or more circuits to share a c.p.c.(*) - so there's no regulatory demand to do so. (But equally nothing stopping you if you really want to either.) There is an implication that the c.p.c. should be run through the same holes in steelwork etc as the live conductors, which means that the two circuits will have to (mostly) share a common route upstream of the switch, but that's probably not difficult in practice.


    *OK  BS 7671 doesn't say so plainly, but given regulation 543.1.2 describes how to calculate the c.p.c. size common to two or more circuits, it's seems a sensible deduction.


       - Andy.
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  • 0

    If I run an earth cable to the switch from one of the lighting circuits, would I also need to run one from the other lighting circuit incase at some point later on the first lighting circuit is removed for some reason, leaving the other circuit live but with no earth at the switch?



    BS 7671 permits two or more circuits to share a c.p.c.(*) - so there's no regulatory demand to do so. (But equally nothing stopping you if you really want to either.) There is an implication that the c.p.c. should be run through the same holes in steelwork etc as the live conductors, which means that the two circuits will have to (mostly) share a common route upstream of the switch, but that's probably not difficult in practice.


    *OK  BS 7671 doesn't say so plainly, but given regulation 543.1.2 describes how to calculate the c.p.c. size common to two or more circuits, it's seems a sensible deduction.


       - Andy.
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