Nuisance tripping saga continues

[Octopus]

All, I'm up for suggestions re the following "case".

House had nuisance tripping - did fault finding but didn't find anything conclusive. Issue for the home owner was that the single RCD was betweem the DNO and consumer unit so when it happened they lost everything and over Xmas this was happening every 10 minutes or so (so they said). Interestingly even though the tripping seemed to be mainly the "fault" of one circuit it could be set off by 4 out of the 7 circuits (I'd asked them to keep notes!)

Because the house is very old with various additions, I recommended a consumer unit change to a fully loaded RCBO set - with a caviat that it wouldn't remove the issue, more like narrow i down to a circuit.

Yesterday I installed the new consumer unit and did another full test of the house, the readings were almost the same as the previous set.

As the day wore on the dowstairs lighting circuit started tripping - and got worse as the day got darker.

No other circuits were tripping.

The only other variable was that it had been raining. Previously the owner had said that heavy rain didn't seem to affect it but horizontal rain or thawing snow did!

I could only get it to trip using a switch position which is one "4 gang hamilton" moduled set of dimmers.

So could the dimmers be the partly responsible? or moisture behind the switch? (none obvious) or a connection between the switches and the sets of lights?

One other thought was to remove the RCBO and install a MCB in its place??!!

Any comments, questions or suggestions would be welcome

 

[Octopus]

Hi

Out of interest what were your IR results for the offending cct.

The IR tests results were good, not to hand but from memory well over 10, much higher than the socket circuits!

 

[pauljpickering8]

Find where the outside light is taken from inside and dis-connect it for a day or so see if that helps. thats what i'd try.

 

[Octopus]

All, thanks for your comments. Just been speaking to the client and it would seem that the tripping continues - specifically on one circuit.

I've got a spare 6A MCB and am considering taking out the RCBO and putting in the MCB until I can get back in with enough time to investigate further - any views on this thought please?

 

[pushrod]

All, thanks for your comments. Just been speaking to the client and it would seem that the tripping continues - specifically on one circuit.

I've got a spare 6A MCB and am considering taking out the RCBO and putting in the MCB until I can get back in with enough time to investigate further - any views on this thought please?

personally i wouldn't as you are leaving the installation in a potentially more dangerous state.

can't remember everything that has gone before - did you try swapping the rcbo?

 

[bugsy]

have you checked all the outside lights , could be moisture causing N/E fault which would trip the rcbo when any of the lights were energised on that circuit

 

[Octopus]

Been back today with for a fresh look.

The tripping had continued, only on the lighting circuit, so much, that they had resorted to using plug in lights!

Analysis, 3 kitchen lights, 4 under cupboard lights, 4 + 6 downlighters, 3 outside lights, 3 wall lights - so not too much to do!

1. Disconnected outside lights - tripping continued!
2. Released 1 kitchen light fitting, but left connected - still tripping!
3. Released 2nd kitchen light fitting, but left it connected - tripping stopped!!!
4. Left all lights on for 1/2 hour - nothing tripped
5. Reconnected outside lights - nothing tripped
6. Refitted 1 kitchen light - nothing tripped
7. Refitted 2nd kitchen light - tripping returned!!
8. Removed 2nd light fitting completely - nothing tripped

Now have light fitting to do a PAT test on it to see if its something internal!

Happy customer (so far)