Rcd problems

[sidekick]

Just fitted dual RCD consumer unit. Wiring old and no earth on light circuits. Customer does not want me to disturb newly decorated and new carpeted house so new consumer unit with testing is as far as i can go.
However, on fitting consumer unit, at least four circuits trip the RCD. I tested insulation values before i started the change and all were ok. Even though wiring old it still looks in good condition.
With the suspect circuits off RCD stays on but test button in effective. Circuits on and it trips.
If I put all circuits on same RCD it still trips.
Any ideas on best way to find the problem. Currently left without RCDs connected ( not good but at least MCB board better than old rewireable board removed)

 

[GLENNSPARK]

any smokes and/or heats in here....dont assume their on their own circuit...or even fed of lighting circuits....0.5 MEG....it may be a hidden load may that fella....

 

[GLENNSPARK]

always IR test at 250VDC first wont you mate...just in case...

 

[Strima]

What state is the insulation in on the VIR (rubber) cables.

No telling what the state of the cables are under the boards and your IR reading hint at the rubber insulation starting to perish.

I'd start to split the circuits down and IR test to find the fault, checking for the hidden FCU with a neon that's probably stashed being a cupboard.

 

[GLENNSPARK]

What state is the insulation in on the VIR (rubber) cables.

No telling what the state of the cables are under the boards and your IR reading hint at the rubber insulation starting to perish.

I'd start to split the circuits down and IR test to find the fault, checking for the hidden FCU with a neon that's probably stashed being a cupboard.

its usually at the terminations where VIR is shot....but along its length..where the oxygen hasn`t had a chance to get to the rubber insulation underneath..it tends to be ok...usually.....it will also depend on how many faults it has been subjected to in its lifetime...and the levels/magnitude...

 

[electric-ian]

This may be useful info for you re. the unearthed metal fittings.

http://www.esc.org.uk/fileadmin/user_upload/documents/industry/best_practice/BPG1v2_web.pdf

Page 5 does recommend you decline to replace the consumer unit if they won't change the fittings.......bit late for that I guess!

Good luck anyway

 

[Guitarist]

With no cpc on lighting circuit you must stress how important it is to change the fittings to class 2 if she won't let you install new cables. As already said, (tho too late now) I won't change a CU if a customer doesn't agree to either.

 

[Octopus]

Interesting as the OP said the IR was ok!

 

[telectrix]

Interesting as the OP said the IR was ok!

can't always rely on IR tests. sometimes readings are OK but still trip RCD. could be due to the fact that you're testing with D.C.

 

[Farmelectrics]

good luck mate think i would of swerved this job specially when they said no damage to decour

 

[SparkyBrad]

It cannot be interconnected neutrals! if you put all circuits on one RCD then stolen neutrals would not become an issue. I personally would double check IR on each circuit. Old rubber insulation sounds suspicious to me. If not ensure all equipment is disconnected when energised. If IR is defo ok then try another RCD unit. If safe switch on RCD unit and try switching mcbs on in different orders to see which ones trip it and if in another order it still happens.

It is possible that you have Earth leakage or 10mA on each circuit adding up to 40 mA in total. Do a ramp test with the other circuits on this can give a good indication of the true RCD trip current.

 

[J&M Electrical]

I'd run.



lol, good luck in sorting it tho, problems like this are a nightmare.

 

[GLENNSPARK]

It cannot be interconnected neutrals! if you put all circuits on one RCD then stolen neutrals would not become an issue. I personally would double check IR on each circuit. Old rubber insulation sounds suspicious to me. If not ensure all equipment is disconnected when energised. If IR is defo ok then try another RCD unit. If safe switch on RCD unit and try switching mcbs on in different orders to see which ones trip it and if in another order it still happens.

It is possible that you have Earth leakage or 10mA on each circuit adding up to 40 mA in total. Do a ramp test with the other circuits on this can give a good indication of the true RCD trip current.

or get it clamped..

 

[GLENNSPARK]

but yes...a ramp test should give the game away if its that...

 

[sidekick]

any smokes and/or heats in here....dont assume their on their own circuit...or even fed of lighting circuits....0.5 MEG....it may be a hidden load may that fella....

No defo no other loads so thinking must be that RCD spur. Calling Monday to look again.

 

[sidekick]

always IR test at 250VDC first wont you mate...just in case...

Thanks for that. Always do.