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nickblake
Yes i bet you have all gone oh not again and normally i wouldnt even post one like this as normally easy faults short here short there problem solved but this one has got even my tiny mind baffled , new install all tested out 100% ok all R1R2 reading satisfactory all insulation reading over 200 meg lighting circuits with and without the switches on all Zs readings well within permitted levels then comes power up all worked then suddenly one circuit tripps with a nice pop and knocks out the RCD as well as the MCB , ting retest the circuit R1R2 0.86 insulation 200 200 200 plus Zs 1.21 ,all clear reset MCB RCD all ok , then for no reason bang MCB tripps re tested circuit all reading as previous its not water in the system as not going out side ,all connections are fine and sound , so i replaced the MCB and has not tripped since , why there is nothing in the MCB to cause a short how , i may be getting tiard but this ones got me , the circuit has been tested 5 times and all insulation tests are 100% ok no shorts and no blinking low energys in the install every thing GLS so im ruling them out all lights were on for over 4 hours after the ?MCB was replaced , it a head scratcher how could an MCB be faulty like that