Bizarre RCD tripping fault

[PheonixFoX12]

Disconnect wir from loft light
Re try
Trips......not the light
Doesn't trip....probably the light
Fit a MKI lamp
Retry

Great will do! Thanks.

 

[SPECIAL LOCATION]

Bizarre RCD tripping fault? Probably NOT... {reality generally tends to prove Bizarre is very very rare}

Dubious investigation and testing methods? Possibly YES!

You say you are a 2nd Yr apprentice...
So at this stage it is quite possible you could get distracted up various garden paths by making wrong assumptions...

I would get your head back into the Basics of proving any circuit... ( Be it new install, Alteration, or Faulty existing circuit.. )

You need to confirm if you have dodgy wiring or a failed/failing accessory...

So the first question ALWAYS has to be..
Are there any Electrical Certificates or Periodic Inspection Reports available for the installation and/or the suspect circuit?
Bearing in mind that Electrical certification has been a requirement of BS7671 for a very very long time...
And Part-P related work has required proper certification for 16+ years as that came into effect in April 2006!

If not then keep in mind that not all previous work may have been tested or certified to BS7671
And.. do NOT forget the 'ESSENTIAL GOLDEN RULE OF FAULT FINDING'...

i.e.
Assume EVERYTHING is faulty, Until YOU have proven otherwise...
(Plus do NOT trust anyone else's suggestions, OR any circuit labels or descriptions).

So with the above in mind.. I would probably start with..
[1] disconnect loads and test the RCD to verify that it is working correctly i.e. Not tripping below 15ma..
(A ramp test would be useful if you have access to a suitable tester?)

[2] Do full dead tests of continuity and Insulation Resistance on ALL circuits that you suspect may be relevant to your problem...

[3] Remember to keep the CPC connected to the main earth terminal and any relevant bonding in place, whilst doing IR test, or you could be disconnecting a potential fault path for your IR tests..

[4] Have you checked if the RCD is actually disconnecting BOTH poles? e.g. loft light getting neutral via RCD.. BUT RCD not actually disconnecting the neutral when it trips?

[5] .. Sorry... Friday Night Beer Overload...
Start with points {1] to {4]...

Then come back to us when I am more soberificated!!

Sounds like an interesting case to crack PheonixFoX12!!
Keep going and please keep us updated with your findings.....

Now I shall open another or maybe.. etc..

 

[Sidewinder]

@PheonixFoX12, please don't take any offence at the posts made to try and help you.
The members are all taking their personal time to write the posts to help you.
Sometimes, posts can be misunderstood, but these have all tried to be helpful so far.

 

[Murdoch]

I’d start by putting my earth leakage clamp meter on the tails

 

[Mike P]

It could be a borrowed neutral, as suggested above or the neutral of the upstairs (loft) lighting may be on its own circuit and wired into (live into upstairs lighting and neutral phase conductor into wrong neutral block in the consumer unit)

 

[PheonixFoX12]

Thanks alot guys for all the inputs into this scenario. Trying my best not to overthink things and keep things simple might not need to jump to testing straight away.

I don't currently have the means of testing the installation but I would say that full dead testing may bring something up. CRIPPER.

What's the likelihood of a borrowed neutral? This problem has not always existed only really in the last few years.

Not taking any offence to these posts im very appreciative of the help

 

[PheonixFoX12]

Bizarre RCD tripping fault? Probably NOT... {reality generally tends to prove Bizarre is very very rare}

Dubious investigation and testing methods? Possibly YES!

You say you are a 2nd Yr apprentice...
So at this stage it is quite possible you could get distracted up various garden paths by making wrong assumptions...

I would get your head back into the Basics of proving any circuit... ( Be it new install, Alteration, or Faulty existing circuit.. )

You need to confirm if you have dodgy wiring or a failed/failing accessory...

So the first question ALWAYS has to be..
Are there any Electrical Certificates or Periodic Inspection Reports available for the installation and/or the suspect circuit?
Bearing in mind that Electrical certification has been a requirement of BS7671 for a very very long time...
And Part-P related work has required proper certification for 16+ years as that came into effect in April 2006!

If not then keep in mind that not all previous work may have been tested or certified to BS7671
And.. do NOT forget the 'ESSENTIAL GOLDEN RULE OF FAULT FINDING'...

i.e.
Assume EVERYTHING is faulty, Until YOU have proven otherwise...
(Plus do NOT trust anyone else's suggestions, OR any circuit labels or descriptions).

So with the above in mind.. I would probably start with..
[1] disconnect loads and test the RCD to verify that it is working correctly i.e. Not tripping below 15ma..
(A ramp test would be useful if you have access to a suitable tester?)

[2] Do full dead tests of continuity and Insulation Resistance on ALL circuits that you suspect may be relevant to your problem...

[3] Remember to keep the CPC connected to the main earth terminal and any relevant bonding in place, whilst doing IR test, or you could be disconnecting a potential fault path for your IR tests..

[4] Have you checked if the RCD is actually disconnecting BOTH poles? e.g. loft light getting neutral via RCD.. BUT RCD not actually disconnecting the neutral when it trips?

[5] .. Sorry... Friday Night Beer Overload...
Start with points {1] to {4]...

Then come back to us when I am more soberificated!!

Sounds like an interesting case to crack PheonixFoX12!!
Keep going and please keep us updated with your findings.....

Now I shall open another or maybe.. etc..

Hope you enjoyed yourself with a few bevvies on Friday night!

Will try to dig out an EICR or EIC from past years on the installation. Believe it was rewired in the 90's.

 

[PheonixFoX12]

Also just confirming that this RCD tripping doesn't occur every time the lighting is switched on.

 

[UNG]

Thanks alot guys for all the inputs into this scenario. Trying my best not to overthink things and keep things simple might not need to jump to testing straight away.

I don't currently have the means of testing the installation but I would say that full dead testing may bring something up. CRIPPER.

What's the likelihood of a borrowed neutral? This problem has not always existed only really in the last few years.

Not taking any offence to these posts im very appreciative of the help

Whereabouts in Lancashire are you if you are not too far from me maybe I could help you out

 

[Mike P]

It could of course just be a faulty RCD that is just on the edge of its spec!

 

[PheonixFoX12]

It could of course just be a faulty RCD that is just on the edge of its spec!

Whats the possibility of that? Could a RCD ramp test prove this?

 

[PheonixFoX12]

Whereabouts in Lancashire are you if you are not too far from me maybe I could help you out

Thanks alot for the offer mate much appreciated. However not so sure its that urgent of a problem to be solved as we hardly go up into the loft anyway just for storage really.

Just inconvenience for lighting i suppose.

 

[UNG]

Thanks alot for the offer mate much appreciated. However not so sure its that urgent of a problem to be solved as we hardly go up into the loft anyway just for storage really.

Just inconvenience for lighting i suppose.

As you are an apprentice I was thinking it would be more of a learning opportunity for yourself, I could bring the test gear and my experience and you would get some hands on fault finding experience and guidance as I wasn't planning on doing it all for you
While I understand your thinking about infrequently going in the loft I have come across problems like this where there was 2 circuits with fault on each that when combined caused the RCD to trip, so it is entirely possible that a fault is developing that may become dangerous with continued use so it may be worth carrying out an EICR just for peace of mind

The offer still stands for the future if you change your mind