RCD on new consumer unit

[dmccormick]

We're having quite a lot of alterations done to our upstairs including moving bathrooms. We've just had electricians in to rewire the upstairs and fit a new consumer unit (old one was circa 1974) for a fixed quote.

The new CU has an RCD and upon completion of the job they couldn't get the RCD to set. They said it must be a fault on our existing downstairs wiring and that they can't be expected to locate and find it within the fixed quote on the upstairs. For now they have somehow bypassed the RCD.

Is what they say reasonable - one of our reasons for getting a new CU was for the safety of RCD protection which we now don't have. Should they have been expected to make it work properly for the original price and is there any way we can be sure the fault is on the old wiring and not the new that they have installed ?

 

[dingbat]

No final circuits should have been connected to the new CU without being tested and if everything was okay the RCD would not have tripped. At the very least they should have isolated the fault and quoted for rectification.

Do you have an installation certificate for this job? (You should have)

 

[Lectrician]

True, the circuits should have been tested. Oviously one has a fault (probably a N to E fault).

I dont think they should be expected to fault find in the fixed price, but they shouldn't have left you with a by-passed RCD either.

 

[dmccormick]

Thanks for the comments.
The guys who did the job work for a large electrical contractor company and did it yesterday as a "foreigner". i.e. I imagine the parts came from their employer and there is no official certificate for the work. The England match was about to start hence their eagerness to depart.

We witheld part of the payment whilst we sought advice as to whether what they were saying was reasonable. I guess what you are saying is that it was - their fixed price wouldn't include fixing the downstairs, but the problem does need fixing.

They will be coming back to look at it again. Is there any way to be sure the fault is on our existing circuit and not what they have just installed. What sort of fault could it be in any case - are we at risk of a shock using the downstairs sockets ?

 

[Lectrician]

I suspect it will just be a N to E fault on gnd floor sockets (very common with a CU replace).

The fault will sit undetected for years, and is immediatly dangerous. It DOES need fixing however.

It would usually take no more than an hour or two to find the fault with the correct meter, and if you are lucky it will simply be a squashed cable behind a socket. It could be a nailed cable in the wall or under the floor, and this could prove tricky to repair. If it is a damaged cable, there are ways around this usually. If it is a ring circuit, the ring could be broken into two radials easily.

Let us know the outcome, we will let you know if you have been stiffed or not.

foreigner?? you mean PJ (private job??)

 

[dmccormick]

Thanks Lectrician. Will let you know the outcome. And yes foreigner = private job - basically a bit of Saturday extra cash for them, probably using "spare" parts from their company. I know if you buy cheap beware, but they are professional electricians doing the job every day so I expect that they've done it properly really.

 

[plugwash]

is the CU a split load?

if it is then you should be able to safely remove the rcd bypass with the main CU isolation off

if not then someone is going to have to pull the service fuse again before touching the CU at all and doing so is not generally reccomended for diyers

once the rcd bypass is removed here is how to test the cuircuits

you will need a multimeter (even the really cheap ones maplin sell for less than a fiver will do for this)

put it on its highest resistance range disconnect all cuircuits that are on the rcd side of your cu and meter them neutral-earth

most of them should read as infinite (same as when the probes aren't touching anything) those that don't need further investigation

 

[securespark]

They may have just put the dicky circuit on the unprotected side.

I always say to customers that circuits may prove to be faulty upon testing, and any rectification is not included in the fitting of a replacement CU.

 

[dmccormick]

I think the CU is split load - it is made by Wylex and the left hand side says "Circuits protected by RCD" and is coloured red. The RHS says "circuits not protected by RCD" and is coloured green. The RCD switch itself is in the middle and on the far right is a double red main switch.

 

[plugwash]

yep thats is a split load

turn off the main switch and take the lid off and look for any wires bypassing the rcd

if in doubt take a photo

 

[dmccormick]

Just to check - I only need to disconnect the neutral wires, one at a time and then check the resistance between it and the earth bar right ? I don't need to disconnect the live wires from the MCB as well ?

 

[plugwash]

yeah that should work ok

it is adviable to unplug everything before you start though

 

[ban-all-sheds]

Just to check - I only need to disconnect the neutral wires, one at a time and then check the resistance between it and the earth bar right ?

I'd suggest disconnecting both neutrals from the ring circuits, or you'll see a very low resistance reading....

 

[plugwash]

yes its important to remember that a ring is one cuircuit

 

[Lectrician]

And, although you can leave the reds in the mcb's, make sure the mcb's are OFF, or you will read all circuits together!!

If the results come back clean, you will need to use a megger in place of your multimeter to find the fault, this is best left to a spark, as they are specialist kit.

It could also be a shared neutral across the rcd. Seen this where a wall light had its live from the switch, and the neutral to a socket directly below it.