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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

    Sparkingchip:

    Have you done a global insulation test between both lives connected together to earth with all the loads connected, then narrowed it down from there?


    Andy Betteridge 




    I did not do a global test, but did test many appliances individually at 240 Volts. No appliance fault was found. Thinking about it now, the nuisance tripping is related to load current. The kettle tested o.k. but always tripped off the R.C.D. if the freezer and fridge were running. The fridge or freezer would trip the R.C.D. on startup, but on other occasions the R.C.D. stayed on if the loads were limited in number. Perhaps we have a rusty nail through a cable or a socket screw just piercing a N. in a damp metal backbox.


    Z.

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  • 0

    Sparkingchip:

    Have you done a global insulation test between both lives connected together to earth with all the loads connected, then narrowed it down from there?


    Andy Betteridge 




    I did not do a global test, but did test many appliances individually at 240 Volts. No appliance fault was found. Thinking about it now, the nuisance tripping is related to load current. The kettle tested o.k. but always tripped off the R.C.D. if the freezer and fridge were running. The fridge or freezer would trip the R.C.D. on startup, but on other occasions the R.C.D. stayed on if the loads were limited in number. Perhaps we have a rusty nail through a cable or a socket screw just piercing a N. in a damp metal backbox.


    Z.

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