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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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    So in my example of plastic conduit and plastic switch and box coming from a steel trunking, it is actually a two gang switch on two different circuits, it is acceptable to have (in this example) just a live and switch live for each circuit down to the switch but an earth isn’t required as regards eddy current considerations as there can be no possibility of an earth fault at the switch due to its plastic construction?



    That's about the size of it!

     

    Please see 411.3.1.1



    I'd suggest otherwise.


    If it's an all-insulated switch then protection against electric shock is by double or reinforced insulation rather than ADS (how could ADS operate without any earthed metalwork?) Thus it's not section 411 that applies but 412. It's therefore the (not greatly dissimilar) regulation 412.2.3.2 we should be looking at. 412.2.3.2 does have a get-out though (via 412.1.2) where the system is controlled so that unauthorised changes (such as the introduction of class I accessories) can't be made.


       - Andy.
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  • 0

    So in my example of plastic conduit and plastic switch and box coming from a steel trunking, it is actually a two gang switch on two different circuits, it is acceptable to have (in this example) just a live and switch live for each circuit down to the switch but an earth isn’t required as regards eddy current considerations as there can be no possibility of an earth fault at the switch due to its plastic construction?



    That's about the size of it!

     

    Please see 411.3.1.1



    I'd suggest otherwise.


    If it's an all-insulated switch then protection against electric shock is by double or reinforced insulation rather than ADS (how could ADS operate without any earthed metalwork?) Thus it's not section 411 that applies but 412. It's therefore the (not greatly dissimilar) regulation 412.2.3.2 we should be looking at. 412.2.3.2 does have a get-out though (via 412.1.2) where the system is controlled so that unauthorised changes (such as the introduction of class I accessories) can't be made.


       - Andy.
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