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On completion of some recent minor work , I carried out the usual testing and noticed the incoming 100A 30mA rcd on the Consumer unit was failing to trip at X1 and X5 at both 0 & 180 degrees Further investigation revealed that the test button on the device failed to trip it as well . All well and good so far faulty RCD me thinks . How often do these devices actually get tested by the end user (despite the quarterly test label ) Replaced it . Checked again and although test button now trips, it still fails to pass RCD ramp or time tests ? Just in case the replacement unit was faulty ( however unlikely ) , I had another unit on the van changed that out with the same result .
Earth loop impedance testing on both on the ring final and incoming Ze, very low reading less than 1 Ohm bearing in mind this is a TT installation ( does seem exceptionally low,) I have checked all round the incoming supply head no sign any PME link I may have missed ????

Any ideas fellow sparks
 
On completion of some recent minor work , I carried out the usual testing and noticed the incoming 100A 30mA rcd on the Consumer unit was failing to trip at X1 and X5 at both 0 & 180 degrees Further investigation revealed that the test button on the device failed to trip it as well . All well and good so far faulty RCD me thinks . How often do these devices actually get tested by the end user (despite the quarterly test label ) Replaced it . Checked again and although test button now trips, it still fails to pass RCD ramp or time tests ? Just in case the replacement unit was faulty ( however unlikely ) , I had another unit on the van changed that out with the same result .
Earth loop impedance testing on both on the ring final and incoming Ze, very low reading less than 1 Ohm bearing in mind this is a TT installation ( does seem exceptionally low,) I have checked all round the incoming supply head no sign any PME link I may have missed ????

Any ideas fellow sparks
Are you sure it's not a 100mA rcd main switch?
Being a tt
 
Hi Ian that was quick. yes it was 30mA . I even increased the setting on the MFT to 100mA and 300mA in an effort to induce a tripping current
 
Bet you the fridge is giving you false test reading turn all mcbs off and test again as above do not test rcd with load connect
 
Is this problem because it's a TT or because as Tel says 'a neutral earth fault' within the installation. I'm interested now.
 
True unless that anomaly of N/E relationship that has been mentioned in past that will cause RCD not to trip in normal operation.
 

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