RCD Tripping.....External influences...

[dlt27]

Had quite a few problems lately with rcd's on dual boards tripping and on 2 occasions I haven't been able to find the problem (trips once every couple of days) . I have meggered circuits, ramp tested rcd, used megger mA meter for earth leakage etc. On both occasions there was an earth leakage of 10mA for entire board so shouldn't trip rcd. However I changed rcd to rcbo's and haven't had a call back since.
I have heard in the past people saying about external influences causing rcd's to trip. However I don't understand how this works. Can somebody explain in simple thick electricians terms how this can happen. The funny thing is with the last rcd the owner said it only started tripping since eon replaced an 11KV overhead cable.(Last one was taken down live by tatters). Thanks to anyone who has patience to explain....

 

[Darkwood]

Is the supply from a pole transformer close by and are other properties adjacent to this property?

 

[dlt27]

Yes and yes please explain why this makes a difference....

 

[Darkwood]

I only ask because i recall a similar experience my old partner had and we eventually put it down to circulating eddie currents within the earthing system possible between properties .... our other theory was mains distortion due to proximity of transformer.... sorry can't nail this one on head but you would require a power analyser to monitor and record all transients and distortions..... was there heavy rain fall or saturated ground at the times of tripping?

 

[dlt27]

I don't think the ground was saturated. What is mains distortion. Sorry if its obvious. I haven't been doing electrics that long...

 

[GLENNSPARK]

Is the supply from a pole transformer close by and are other properties adjacent to this property?

are you thinking along the lines of spikes appearing in neighbouring installs here Dark?...
a bit like the old voltage trips?

 

[Darkwood]

are you thinking along the lines of spikes appearing in neighbouring installs here Dark?...
a bit like the old voltage trips?

Well we never pinned the issue down ...... cheaper to fit rcbo's throughout than keep returning but it seemed to clear.... and no rcd's work on balance now so don't suffer the same fate as when the earth was monitored for current alone..... others have had same issue but ive yet to get a good solid answer but common factor is a pole transformer and close proximity to property.... even 11kv overhead or close by may possibly cause nuisance tripping if induction is considered. Im open to suggestions myself.

 

[GLENNSPARK]

Well we never pinned the issue down ...... cheaper to fit rcbo's throughout than keep returning but it seemed to clear.... and no rcd's work on balance now so don't suffer the same fate as when the earth was monitored for current alone..... others have had same issue but ive yet to get a good solid answer but common factor is a pole transformer and close proximity to property.... even 11kv overhead or close by may possibly cause nuisance tripping if induction is considered. Im open to suggestions myself.

interesting one this:
i remember this one time we kept having to go back to this bloody house...
i ended up refering to it as `the RCD house`..
as in `are we going back to the RCD house today Leigh?`....lol
we tried all the usual: Ramp, EL testing, PAT on appliances...all came back good..
now, at that time i had a chance to get my mitts on a powersense power line monitor:



their really for IT suites but i thought if i could somehow rig it up to catch a bit of data in regards to this RCD random tripping phenomenon....

 

[Marvo]

I had a nuisance trip a couple of years ago that I eventually tracked down that it coincided every evening when the street light on the road outside the property switched on. I never got to the bottom of the actual cause or correlation although I suspected maybe harmonics. I remember the brand was Gewiss and I replaced it with a different make and that was the end of it. I even reused it later in another DB and it passed all the usual tests and has been trouble free to date.

 

[Darkwood]

Here's the answer although its a long read and ignoring the basics at the beginning you'll find by the end you'll see nuisance tripping similar to these situes we encountered.... ps ive had the streetlight one myself.

Marc's Technical Pages: Power Quality Symptoms and Solutions - Nuisance Tripping

A good read though very enlightening.

 

[Richard Burns]

So it is all these electronic bits of kit (outside the home) that cause problems!!

 

[Darkwood]

After reading that it does bode well and explains why a Close proximity pole TX as well as neighbouring properties could all have bearing on the causes of nuisance tripping ...

We need to be careful we don't assume this to be the cause as all other options and tests should be carried out first and the majority of nuisance tripping won't ever get this technical with regards to capacitive leakage and heavy load switching of other properties, the above issue ive found is very rare and is a last resort to consider after all other avenues have been exausted.

 

[Darkwood]

To the OP .... read my link in full ...dont worry if you dont understand it but basically because you have already got 10mA leakage the rcd can trip between approx 16-30mA thus may only be 6mA short of its threshold now due to the nature of the TX been close and other properties sharing it it can create an imbalance that can be detected by the rcd .... changing to rcbo means you have shared the accumulative 10mA across many rcbo's and this is why your may have resolved the problem...

PS ... your just unlucky to get this issue due to this set-up as most sparkies will do there full time never coming across it ever so treat it as a one off and always revert to what you understand about tracing nuisance trippings.

We will assume with my replies that you have correctly shown no other issues are creating the tripping like an intermittent fault caused by a possibly an element which may test clear but can once hot fault/leak to earth do to expansion or the compressor motor on fridge on its way out etc etc....

 

[Guitarist]

I had a situation a few months back which turned out to be the ignitor on a gas hob. It was plugged in behind the cooker, and occasionally, when the Lady of the house wiped the hob down, water was trickling down the ignitor switch and shorting to the body of the hob. Then it would dry out and be fine. Took me quite a while to find that one...

 

[Gazthesparky]

I had a similar situation a few years back I got called to a house where a front end RCD protecting a t&e feeding a fuse box in the garage kept tripping

Carried out all the tests ect no probs ended going back a couple of times thought I'd tracked it down to be water getting into the cooker switch so changed that but that didn't help.

Last time I went back to site I was fiddling in the meter box outside when the neighbour came out and said he was having the same problem. While I was there there was a power cut and a huge lump appeared in the pavement. It turns out that there had been a fault on the supply cable and it was tracking back and tripping the RCDS

They fixed the cable and I also got extra work from replacing the fuse boxes for at the time 16th edition consumer units. I removed the t&e sub main and front end RCD and installed swa and a switch fuse

Turns out that the neighbours had, had the same spark a few years before move the fuse boxes from inside to the garage and he had run t&e and installed a front end RCD instead of just upgrading the fuse board to a consumer unit