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Loss of neutral

lyledunn
I have just been involved in a situation where temporary loss of neutral on a TNCS system caused thousands of pounds worth of damage. It seems this loss of neutral situation, either within or outside the installation, is occurring more frequently. SPDs are now commonly fitted but at DBS  and generally with a Up in the order of 860v, so giving no protection on loss of neutral in a three-phase and neutral system. Cost benefit analysis across the national spectrum might not support a compulsion but is it time designers should be raising the issue with clients and at least offering a solution. On the other hand, is there a packaged solution?
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    mapj1:

    I have fitted capacitors N-E after a 4 pole RCD, so that if the NE voltage rises, the RCD sees the N-E current and fires and breaks everything but the CPC.

     


    Just interested on people's views as to whether this stacks up with Regulation 531.3.1.202 ?

     



    531.3.1.202 It is not permissible to introduce an external connection for the purpose of intentionally creating a residual current to trip an RCD.





    However, I am compelled to point out that I'm asking this question with the full knowledge that many appliances have a capacitor connected between N and PE - but we are talking about of orders of magnitude difference in capacitance (1-10 nF in appliances, vs perhaps 10-20 μF to trip a 30 mA RCD for an N-E voltage of 50 V)?

    Just edited to note that this Regulation was introduced in BS 7671:2018, and therefore I'm not necessarily saying that Mike's application was non-compliant at the time.


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  • 0
    mapj1:

    I have fitted capacitors N-E after a 4 pole RCD, so that if the NE voltage rises, the RCD sees the N-E current and fires and breaks everything but the CPC.

     


    Just interested on people's views as to whether this stacks up with Regulation 531.3.1.202 ?

     



    531.3.1.202 It is not permissible to introduce an external connection for the purpose of intentionally creating a residual current to trip an RCD.





    However, I am compelled to point out that I'm asking this question with the full knowledge that many appliances have a capacitor connected between N and PE - but we are talking about of orders of magnitude difference in capacitance (1-10 nF in appliances, vs perhaps 10-20 μF to trip a 30 mA RCD for an N-E voltage of 50 V)?

    Just edited to note that this Regulation was introduced in BS 7671:2018, and therefore I'm not necessarily saying that Mike's application was non-compliant at the time.


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