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Downstream rcd tripping

Nick Bennett
Afternoon all, I had abit of a funny one this morning. Carrying out some work at a block of flats. 

DId a Ze at the landlords board to find the main earth had been cut off! Did a Ze between the live and the stub left on the side of the ryefield. This then tripped out some of the downstream RCDs feeding tenants flats. I assume that I'd in balanced the neutral. Just wondering if anyone else had had this.

I've called in ukpn to check the earthing and to get it fixed.
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    If the RCD fires it thinks it is seeing an L-N imbalance.  If there is an NE bond  in one of the flats, perhaps deliberate  to get some sort of earthing back or perhaps a faulty water heater, then things like plumbing may be neutralled, rather than earthed.

    In that case, you may be bypassing the neutral sensing coil in the RCDs.

    Or it may just be a transient effect inducing a short duration pulse and taking an RCD already near the edge, over it - how big was your test current.

    It is possible once the main earth is fixed, that some remedial works are needed in at least one of the affected flats.

    M.
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    Hi MapJ

    thanks for the response. I can well imagine there will be some remedial works required. Though from what I've seen so far, it's all ok, except the lack of earthing. There aren't any water heaters, only sockets, lights and cooker per flat. 

    The landlord is abit of a DIY type so could well be something hidden.
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    It must be reasonably obvious that the Earth connection has been removed because there is a fault somewhere. Why not IR test the whole lot from where you are, because that is the fault to find. Some of the flats tripping might well be the result of a N-E short and the parallel path through the piping or something similar. Just take it slowly and you will find the problem. Exactly why they tripped will probably become clear as well. Work from the data!
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    Nick Bennett:

    I've called in ukpn to check the earthing and to get it fixed.


    I have been wondering about this. Isn't the lack of earthing a C1?


    Put another way, if you disconnect the earthing conductor in order to measure Ze, you either isolate the installation or take steps to ensure that nobody is using equipment during the test procedure.


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    I went there this morning to replace a light. I've since told him he needs to have the whole place checked. 

    There was clearly an earth provided originally because there's a stub still attached to the side of the sealed ryefield. That's UKPNs territory hence the call to them.

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    It may be part of the building network - depending where the metering is done and the detail of the distribution  UKPN may decide its not theirs. If so, come back..

    UKPN guide to BNO/DNO demarkation.

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