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)

 

[Spazz]

As we are on this topic - a quick reminder - this only applies for systems with earthing. Dont forget you have IT systems with NO EARTH, NO Bonding, etc.

These also dont come under the BS7671 regs either.

 

[spark 68]

These also dont come under the BS7671 regs either

Sorry to disagree here Nick, but IT systems do fall under BS7671, but they are not allowed in domestic, and also they have to be under supervision by skilled personnel.

 

[Spazz]

I might be wrong with that so hold my hands up! (about the It systems in BS7671)



A property about 5 miles from me, has an IT system.

Back to this property, to get to it you have to go through a tunnel with a large transformer at the front of the tunnel and another transformer at the house side of the tunnel.
Its an old military unit which was used back in the 2nd world war for refueling the big ships that came into the port here.

The transformers are to increase the voltage to get through the mountain and then step down to 230v again for the property.

This domestic house belongs to a school teacher who does not have a clue!

 

[telectrix]

I might be wrong with that so hold my hands up! (about the It systems in BS7671)



A property about 5 miles from me, has an IT system.

Back to this property, to get to it you have to go through a tunnel with a large transformer at the front of the tunnel and another transformer at the house side of the tunnel.
Its an old military unit which was used back in the 2nd world war for refueling the big ships that came into the port here.

The transformers are to increase the voltage to get through the mountain and then step down to 230v again for the property.

This domestic house belongs to a school teacher who does not have a clue!

interesting .... sounds like my kind of a retreat. does it have a moat and a portcullis?

 

[sidekick]

Thankyou all for your comments. My plan is to return and advise customer in writting along the following lines -

1. Insulation resistance values on oven and socket circuits ( not currently on RCD protected side of CU ) are low
indicating possible deterioration of rubber cables.
Faults need to be found with further testing, remedied and added to RCD side of CU with recomendation of rewire
of those circuits.
2. No earth on lighting circuits which have at least x 10 metal wall lights connected.
Customer options are - a) Rewire of those circuits with new t/e
b) Install new earth to each light point.
c) Carry out risk assessment with 3 tests and remedy where required.
Test 1 - Check continuity between each fitting and main earth terminal.
=< 1 ohm fitting earth ok.
Test 2 - Check insulation resistance L/N together with main earth terminal.
=> 1 megaohm means earth fittings ok and safe.
Test 3 - Check insulation resistance L/N together with each fitting which did not
have earth ok in test 1.
=> 1 megaohm means unearthed fittings currently safe.
Any fittings failing test 3 will have to be remedied or removed and label placed on
consumer unit warning of replacing fittings with class 2 only

I already know customer will want no rewiring and at best will allow the risk assessment only.

 

[Spazz]

To be honest give them one option with the lighting
Change all lights to class 2 or rewire.

If there is a fault then your in the dock explaining why you left it like that

Defo put the cooker on the RCD side

 

[electric-ian]

Arrrgh... This thread strikes so many chords!
Lets get the place decorated then we'll get an electrician in.
I reckon people think we have trained moles that burrow up the walls pulling the cables in behind them...

More seriously though, what worries me in situations like this is the liability issue if something goes wrong.
If you do the checks as detailed above, and keep a good record of results, then at least you will have the ESC leaflet to wave if anybody questions your work.

Presumably the switch boxes are wooden if it's rubber cables but if there are any metal boxes you should probably check the IR on the screw heads also - BTW RS do some M3.5 csk nylon screws if you need them.

Good luck

 

[Guitarist]

I'm going to stick my tin hat on and dissappear down into my bunker but....

There are hundreds of thousands (if not more) of houses in the UK that don't have a cpc on the lighting circuits. Changing the CU for one with dual RCD's or RCBO's, coupled with installing bonding WILL make them safer. A note on the EIC stating that class 1 light fittings is a must.

Taking a position that means you decline to change a CU unless the homeowner won't agree to a lighting rewire is plain daft.

I agree in principal, but if you tell most homeowners that you cannot do the CU change until either class 2 fittings are installed or the lighting cables are upgraded, then I think that many would agree to a course of action. Once it's done, they will simply say "well why did you do the work if it was unsafe?"

 

[GLENNSPARK]

interesting .... sounds like my kind of a retreat. does it have a moat and a portcullis?

sparkys n water dont mix tel....