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Using the drain wire in FP200 plus as a signal conductor... can I?

Michael Brennan
Hi Everyone,


I am looking to find out if it is against BS7671:2018 to use the drain wire in a cable (specifically FP200 plus) as a signal conductor (switched 24VDC signal), or whether this must be used for the earth/shield?  Is there anything in the regs that states what the drain wire must be used as?


Many thanks in advance,


Michael
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    Alan Capon:


    FP200 is readily available as 2 core plus earth, three core plus earth and four core plus earth. Some of the suppliers even sell the “unusual” sizes per metre. 


    Regards,


    Alan. 






    FP200 is even available as a multicore cable with seven, twelve or nineteen cores in with cross-sectional areas from 1 mm² to 2.5 mm² - although probably more of a special order item rather than something to be found in your local electrical wholesaler!


    I wouldn't be overly keen on the use of the drain wire other than for its intended purpose - it just doesn't feel right in the same way as the mis-use of the CPC in 6242Y to provide a third conductor for multiway switching.


    Depending on what the actual application is, there may also be EMC (putting a signal on what should be a screen) and fire resistance (the drain wire isn't protected from fire in the same way as the actual cores) considerations to take into account.


     

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  • 0

    Alan Capon:


    FP200 is readily available as 2 core plus earth, three core plus earth and four core plus earth. Some of the suppliers even sell the “unusual” sizes per metre. 


    Regards,


    Alan. 






    FP200 is even available as a multicore cable with seven, twelve or nineteen cores in with cross-sectional areas from 1 mm² to 2.5 mm² - although probably more of a special order item rather than something to be found in your local electrical wholesaler!


    I wouldn't be overly keen on the use of the drain wire other than for its intended purpose - it just doesn't feel right in the same way as the mis-use of the CPC in 6242Y to provide a third conductor for multiway switching.


    Depending on what the actual application is, there may also be EMC (putting a signal on what should be a screen) and fire resistance (the drain wire isn't protected from fire in the same way as the actual cores) considerations to take into account.


     

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