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R.C.D. tripping and earthing concerns.

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Evnin' All,

                  I have had a hard day and my brain is in meltdown so please excuse nonsense and silliness.


I installed a new socket in a house today. TT earthing presumably. New A.B.C. overhead supply. Nearest D.N.O. P.M.E. pole earth rod about 15 metres away from the house. When I tested the R.C.D. it worked on the test button, but the switch seemed a bit graunchy. It would not trip off on 30mA test, but did trip off on the 5X R.C.D. test at a socket. I replaced the R.C.D. The same thing happened. No trip on 30mA test setting, but it did trip off on the 5X setting.


An earth fault loop test at a socket showed a reading of 185 Ohms.


A  length of 6.0mm2 green and yellow cable was found in the front yard but the electrode is not inspectable as it is covered by block paving is old. It may have rotted away. With the main switch off the resistance from N. to the earth bar in the consumer unit is about 180 Ohms. 


The consumer unit is a 10 way unit with just one 30mA R.C.D.


I converted the earthing to P.M.E. and then nuisance tripping was seen. I intend to install an all R.C.B.O. board tomorrow.


Sometimes a fridge when turned on will trip the R.C.D., other times it is a freezer, then the kettle. But the appliances test o.k. with an insulation resistance test. Once or twice the tungsten lighting circuits tripped off the R.C.D.


I assume that the addition of individual leakage current is responsible for the R.C.D. tripping, but there is no logic to which individual appliances/circuits seem to cause it. Two suspected rings test o.k. for insulation resistance.


The house owner reported that the gas fitter received a shock when doing something under the AGA. The main gas bond was loose at its clamp. I have replaced the earth clamp.


Any thoughts please?


EDIT. P.S. I have a Voltage tester that will trip off a 30mA R.C.D. if connected to the outgoing R.C.D. L. and E. at the same time. When this was connected to the original R.C.D's LIVE INCOMING terminal and the E. bar the R.C.D. tripped off. Did this raise the Voltage on the C.P.C.s sufficiently to trip off the RC.D?


Z.


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  • 0
    making it PME is not as simple as joining N to E on the customer side,  ignoring for now the legal aspect of doing so in the UK.

    The rest of the installation has to be PME ready, with suitable bonding to water and gas pipes, or insulating joints in the service pipes,  and larger CSA earthing in any places likely to suffer from diverted neutral.

    The line to the house has to be suitable, which usually means that all connections in the PEN are double crimped and no screw line taps.

    Strictly the only authority that can know this for certain is the DNO.

    I appreciate that the chance of a PEN fault during a quick diagnostic  test to joint the N and E busbars to see if a nuisance trip problem gets better or worse  is not the same risk as a supply side PEN fault as having them linked for years, hough  I'd very strongly recommend either getting the DNO to do it, or changing it back to TT.

    I'm sure you know this really, so this is just an observation and partly for the benefit of any other readers finding this post in the future who may be inspired.
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  • 0
    making it PME is not as simple as joining N to E on the customer side,  ignoring for now the legal aspect of doing so in the UK.

    The rest of the installation has to be PME ready, with suitable bonding to water and gas pipes, or insulating joints in the service pipes,  and larger CSA earthing in any places likely to suffer from diverted neutral.

    The line to the house has to be suitable, which usually means that all connections in the PEN are double crimped and no screw line taps.

    Strictly the only authority that can know this for certain is the DNO.

    I appreciate that the chance of a PEN fault during a quick diagnostic  test to joint the N and E busbars to see if a nuisance trip problem gets better or worse  is not the same risk as a supply side PEN fault as having them linked for years, hough  I'd very strongly recommend either getting the DNO to do it, or changing it back to TT.

    I'm sure you know this really, so this is just an observation and partly for the benefit of any other readers finding this post in the future who may be inspired.
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