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

 

[rocker]

Are there any outdoor security lights?

 

[Octopus]

Yes. On the same circuit but at a different switch position. Tried on and off a few times but no tripping!

 

[malcolmsanford]

The outside lights looks like a good place to start.

 

[rocker]

Ok..... thought maybe could be something to do with a photocell as you said it got worse as it got darker.

Damp problem somewhere I reckon. Try sticking a regular switch where the dimmer is for the time being and see if that stops the problem, if not I'd wager it's going to be a switch on an external wall, with damp issues from saturated walls or a small leak. Do they have any single storey extensions anywhere, felt roofs etc?? Drip drip drip, trip trip trip.

 

[pushrod]

have you ramp tested and "ordinary" tested the rcd? what rating is it 63A or 80A- it hasn't been cooked by excess load ?

edit had something similar and found rcd was tripping at about 7 to 9mA!

could well be cumulative , with the dimmers being largely responsible

 

[Octopus]

Pushrod.

Re the dimmers and operating only 1 (any one) would cause the trip.

I haven't ramp tested the RCBO as yet, mainly because the characteristics of the tripping are very similar to before.

Rocker

I've not seen a photocell

Malcolm

Operating the outside light switch had no effect - i.e. it didn't trip, whereas operating any of the 4 switches does.


NB: There have been times when the tripping has stopped for weeks!


Thanks for the comments and suggestions so far.

 

[malcolmsanford]

Could they have dried out enough when you teseted for them to work. If your still convinced it may be the dimmer get a set of module switches and put them on, a fault could fry a dimmer but then it would not work, only switch on off.

 

[rocker]

Just for reference, the photocell would nprobably be in the PIR part of most security lights nowadays.

As above really, just put regular switches on instead of dimmers and see if that does anything. You can try IR testing the dimmer in several positions I guess... if that's what seems to be tripping it then that's what you need to look at first.

If it's happening more at night - when does the central heating come on? Is it possible that a cable has been run incorrectly with a hot pipe and is meltiing etc when heating comes on? It could be any number of things.

Have you actually checked for signs of damp/green crap in the backbox?

 

[Octopus]

Rocker, good points.

The issue is in part of the house, which was adapted post "Part P" and there's not a MWC or EIC in sight despite it being a kitchen.

My list of things to look at is getting longer.

Anyone know where I can buy some litmus paper? I'd like to put some in the back of the switch box to see if their is ingress of moisture!

 

[Paul.M]

One thing I came across, a customer had taken down an outside wall light (none pir) and just shoved the cable back into the outside wall. It was shorting out in heavy rain when it came down side ways. Have another look outside even if its just to eliminate the possibility. Also worth checking the water seals in any outside lights + is there a drip loop on the cable? Maybe that a little bit of water is getting into the jb that feeds the light. As above it could be moisture behind the switches, can you hire a damp test meter? Good luck and I hope you find it sooner rather than later.

 

[pushrod]

Rocker, good points.

The issue is in part of the house, which was adapted post "Part P" and there's not a MWC or EIC in sight despite it being a kitchen.

My list of things to look at is getting longer.

Anyone know where I can buy some litmus paper? I'd like to put some in the back of the switch box to see if their is ingress of moisture!

Litmus is for acid/alkali not moisture. Just putting your resistance meter probes in side by side onto the plaster at the back and then comparing to a known dry area would give some indication of relative dampness.

 

[pushrod]

double post!

 

[tony mc]

Hi

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

 

[nickblake]

could test the CDU for eath leakage then each circuit see if anything is drawing more than expected