RCD periodioc testing and reliability

[ericmark]

Looking at the RCD there are many variations including auto resetting and with built in monitors as with the X-Pole.

One would also assume where someone presses the test button and it does not work they will get the RCD changed so visiting random houses is hardly going to give results which can be of any real benefit. If for example a new build estate was selected and all agreed to taking part in the survey then some control would be exercised as to where RCD's were changed.

My wife worked for market research firms for years and she would say how she could change the results just by the inflection in her voice. And clearly were one knows the research is for government some will try to alter the results.

As to the number of bypassed RCD's the question must arise did the faulty RCD's ever work? Clearly no post fitting checks were carried out or there could be no bypassed RCD's found. I am sure I am not alone in having to return faulty RCD's which on fitting did not work. In fact I have found the heavy cables used can warp the unit so causing it not to work as designed so the post fitting tests are very important.

The reports from contractors shows how the information was obtained from many sources and although it serves to show how important an Electrical Installation Condition Report is to be of any real value one needs two reports the PIR then 10 years latter the EICR and compare results so one knows it was all correct to start with.

 

[stillp]

As to the number of bypassed RCD's the question must arise did the faulty RCD's ever work?

The implication of the article seems to be that they worked all too well, and had been shorted out to prevent what was seen as spurious tripping.

(Wasn't there a thread on here a while ago where someone had done just that instead of sorting out his borrowed neutral?)

 

[stillp]

I've always thought that householders should be advised to switch off as many loads as possible before testing an RCD.

But not all loads, or they won't know if the RCD has actually opened!

 

[JohnW2]

Looking at the RCD there are many variations including auto resetting and with built in monitors as with the X-Pole.

Indeed, as you frequently tell us (and thanks for not posting a picture again ), but I think you'd have to look very hard to find anything other than a bog-standard passive type B (or occasionally C) RCD in or around a domestic CU.

One would also assume where someone presses the test button and it does not work they will get the RCD changed so visiting random houses is hardly going to give results which can be of any real benefit.

Exactly my point. Satisfactory experimental design is crucial.

As to the number of bypassed RCD's the question must arise did the faulty RCD's ever work? Clearly no post fitting checks were carried out or there could be no bypassed RCD's found.

That's a pretty wild assumption - this whole discussion is surely primarily about the reliability of RCDs - i.e. the probability and timing of subsequent failure of an RCD that performed satisfactorily when installed? Furthermore, the reasons for failure of many of the 10 RCDs examined by ERA are such that it is most unlikely that these faults were present at the time the devices were installed. It could even be, as implied by stillp, that some of the failures were the result of well-intentioned testing by householders at a time when the RCD in question was heavily loaded.

Kind Regards, John

 

[JohnW2]

I've always thought that householders should be advised to switch off as many loads as possible before testing an RCD.

But not all loads, or they won't know if the RCD has actually opened!

True - as you are presumably thinking, the audible operation and even movement of the manual operating lever does not completely guarantee that the contacts have opened.

Kind Regards, John.

 

[stillp]

Correct!

 

[ericmark]

Personally my gripe about RCD use in the lack of double pole switching after the RCD.

I have seen many switched FCU's in use with RCD protected circuits. So with a fault one can't isolate the neutral to that device without taking the FCU off the wall and disconnecting the cables.

Today with lights with RCD protection one must even question the whole idea of single pole switching where there is not a removable control gear and lamp.

 

[JohnW2]

As to the number of bypassed RCD's the question must arise did the faulty RCD's ever work?

The implication of the article seems to be that they worked all too well, and had been shorted out to prevent what was seen as spurious tripping.

I'm not sure that there is necessarily such an implication, and definitely no certainty of that. All we are told is that 6 RCDs were shorted by a (HA) 'electrician' because of perceived "nuisance tripping" and that none of these devices were returned to ERA for testing or examination. I would suggest that if an 'electrician' was capable of effecting this amazing 'solution' then one can make no assumptions at all about whether or not they will have tested the RCD before bypassing it!

Kind Regards, John

 

[JohnW2]

Personally my gripe about RCD use in the lack of double pole switching after the RCD. I have seen many switched FCU's in use with RCD protected circuits. So with a fault one can't isolate the neutral to that device without taking the FCU off the wall and disconnecting the cables.

I think it's a pretty long time since I last saw a switched FCU with a single pole switch. Lighting circuits are obviously a bit of an issue, since I doubt you'll often find any DP switching on them!

Kind Regards, John

 

[ericmark]

At my parents house when the wet room was being installed the electrician had offered to change to whole consumer unit instead of fitting a mini one just for wet room for £100 extra. Seemed a good deal so we said yes.

When I arrived the electrician was struggling to stop the RCD tripping. He had no spare RCD, no RCD tester, no insulation tester, the only testing tool he had was a multi meter.

I popped to my sons and picked up spare RCD, and 17th Edition test set. And returned finding there was a problem with the existing sockets. An isolator was fitted for that night and the electrician promised to return to complete the work. I found the faulty wiring and removed it but that electrician was never seen again.

Two weeks latter the builder also ran off into the Welsh hills of Corwen never to be seen again.

I am sure he is not the only guy to take chances and run away when it didn't work out. There must be many sub-standard installations where a DIY man called himself an electrician and got it all wrong.

These surveys however are only valid where real electricians have been doing the work. Even with large housing developments electrical firms have been known to employ semi-skilled guys with testers and trouble shooters hopefully finding and correcting errors.

I do see the point made about dust but even that has a lot to do which where the consumer unit has been fitted. And even if the lid has been closed. Just too many variables for the results to be any more than a passing interest.

 

[JohnW2]

These surveys however are only valid where real electricians have been doing the work. Even with large housing developments electrical firms have been known to employ semi-skilled guys with testers and trouble shooters hopefully finding and correcting errors.

Agreed. In the case we're discussing, I think we can can probably agree that someone capable of bypassing an RCD as a (seemingly 'permanent') 'cure' for alleged "nuisance tripping" cannot seriously be considered to be 'an electrician', regardless of what 'qualifications' or experience they may have, or claim to have!

Kind Regards, John

 

[ricicle]

.....and the 2013 award for thread hi-jacking has gone to this one. No need for anyone else to try !

 

[DetlefSchmitz]

.....and the 2013 award for thread hi-jacking has gone to this one.

Surely the OP was asked and totally answered (by you) by post #4? I wouldn't consider the subsequent discussion a hi-jack in that case.

 

[Scoby_Beasley]

I don't really understand that statement. No matter how well designed, constructed and tested an installation may be, it's not going to remain 'as safe as it's going to be' for very long if there is a significant probability that protective device(s) may fail fairly soon after the electrician walks out of the door - even if the BS7671-basedpaper work is pristine and happy!

Kind Regards, John

Bit like an MOT then. Who's to say when you leave the garage you don't pop straight round yer mates and give him back his decent wheels n tyres and slip your bald uns back on. Later the Conservative prefects stop you and, as your defence say "Well here's me MOT officer, couldn't of worn me tyres out already!"

This is not me disagreeing with you, but when someone gets the big pointy stick pointed at them, they'll deny any and everything to cover there own butt.

Who's to say once you're gone the extension lead for the loft herbal farm doesn't re-appear and gets hard wired to the RCD?

 

[JohnW2]

Bit like an MOT then. Who's to say when you leave the garage you don't pop straight round yer mates and give him back his decent wheels n tyres and slip your bald uns back on.

Sort-of, although we're not really discussing anything underhand or naughty here. The discussion is about reliability - which, as I said, I take to refer primariliy to the subsequent development of faults in products which were fine (and which which testing would show to be fine) when first installed.

RCDs which are faulty when bought/installed, and which are not tested (and found to be faulty) at the time of installation (or swaping OK items for faulty ones as soon as the inspection certificate has been handed over!) is a whole different discussion - about something which would not normally be described as 'reliability' (at least, not of the devices ).

Kind Regards, John