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)

 

[truckster]

Sounds like you may have interconnected neutrals somewhere in the house. If it's old as you say there are going to be jb's under the floors, in the loft etc and you never know whats been connected to what. I would start by checking for continuity between the lives and neutrals to see whether that is the case. Could be a right mare!

 

[Engineer54]

Sounds like you may have interconnected neutrals somewhere in the house. If it's old as you say there are going to be jb's under the floors, in the loft etc and you never know whats been connected to what. I would start by checking for continuity between the lives and neutrals to see whether that is the case. Could be a right mare!

I bet that's cheered him up no end!!! ...lol!!

 

[Octopus]

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.

Yuk! not a nice position to be in. What are the 4 circuits? How are the IR readings when the circuits are tested individually?

 

[Guitarist]

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)

What tests did you carry out for the purpose of your EIC?
Also, with no cpc on the lighting circuits, are all the fittings class 2?

 

[drew35]

What make was the new board? I've had Contactum boards on more than one occasion where the neutral cables from the main switch to the RCD's, and RCD's to neutral bars are not routed correctly. It caused the RCD's to trip as soon as any circuit was energised.

 

[telectrix]

good call...... @ OP. check all manufacturer's connections and make sure you've got all your neutrals in the correct neutral bars.

 

[cakey]

sounds like a borrowed neutral or 2. as already said check your neutrals are in the right place in cu. have you tested rcd's? could be faulty.

 

[1shortcircuit]

OP, you wouldn't be the first to mix up Neutrals. I managed to do it myself and there were only four circuits only two of which were on the RCD side lol

Have you separated the upstairs and downstairs lighting circuits? If so, is there a 3 core cable going from the hall switch to the landing switch? Often on older properties there is no 3 core only a single running from one switch to the other.

There are many reasons why this could happen. Best thing to do is take a deep breath and don't panic, clear your mind and think as more often than not the problem is often staring you in the face.

Good Luck, I look forward to hearing how you get on :thumbsup

 

[lowprofile]

I've had this situation a couple of times and on both occasions it was shared or 'borrowed' neutrals that needed to be separated, both times between two lighting circuits.
Now I try to do a quick continuity check between neutral conductors before re-wiring a new CU (don't always remember though)

 

[sidekick]

Thanks to all for your comments.
Have been back today to progress.
Further testing and check neutrals etc gave me the following.

9 circuits -
x 4 for lights, old rubber cable with no earth on any. All insulation tests L/N good, no cotinuity with neutrals and managed to get all 4 on RCD working. Although a lot of metal fittings.
x 1 Shower on t/e red black. All insulation values good and ok now on RCD.
X 3 Socket circuits all with earth on rubber sheathed cables trip RCD and insulation values ok except L/N on 1 circuit.
x 1 oven circuit with earth on rubber sheathed cable trips RCD. Insulation value failed on N/E

 

[Welshsparky]

the fittings will have to come down if theirs no earth to them, Ive just done a consumer unit change in a block of ex council flats, Had the same problems, lets just say i feel 10 years older!

 

[GLENNSPARK]

so the dodgy line-neutral IR on one socket circuit....any neons on it?...

 

[sidekick]

the fittings will have to come down if theirs no earth to them, Ive just done a consumer unit change in a block of ex council flats, Had the same problems, lets just say i feel 10 years older!

just what i've told customer. However,
not happy and don't think there going to comply. Will note my advice on cert and label consumer unit. Done a few jobs here and funny how customer always says she wants to.move when i've been. Cheaper to rewire i think.

 

[sidekick]

so the dodgy line-neutral IR on one socket circuit....any neons on it?...

Thanks but no can't find any. Does read very low at 0.5ohms and just thinking about Rcd spur unit in loft for extractor. Thought it was on light cirvuit up there but will double chevk not on ring next visit.

 

[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