Moving consumer unit - extending cables (again!)

[Grunff]

Having finally decided what we're going to do with the downstairs area, we're going to have to move the consumer unit by about 4 foot. I wish I'd thought of this scenario when rewiring :-(

Some of the circuits I'll be able to simply replace the last leg of cable (from CU back to first socket), while others I'll have to extend the cables.

I've read all previous threads on this, but haven't come across an answer to this query:

Where I have a ring, with two 2.5mm cables going to the CU, instead of extending each of the two 2.5mm cables, can I just join them up and connect to the CU using a single 6mm cable? Anyone see a problem with this?

Just to make sure I'm being clear, the two ends of the ring, currently both ending up in the CU, would instead both go into a 30A junction box. Then a 6mm cable would leave the juntion box and connect to the CU.

TIA

[G&M]

Where is this junction box placed. In theory you are simply copying the arrangement normally in the CU but in a CU one usually tightens up all the screws when you are in there wheras this junction box will probably never get touched again. Screws unfortunately do come loose.

[Grunff]

Well, that's true - but it's also true of screws in sockets and light fittings, which might get tightened once every 20 years or so!

The junction boxes will be going under the floorboards, so accessible but not very easily. I believe that use of junction boxes in this situation is compliant with the regs (screw terminals are ok as long as they are accessible).

[G&M]

Agreed - and I expect a large number of sockets in older installations aren't part of a ring anymore on at least one conductor. It's more that when something goes wrong with your scheme, there's likely to be a very confused electrician wondering what's gone wrong. Of course a message or diagram attached to the inside of the CU might be helpful

Well that's slightly more inaccessable than I stick to but may be OK. What do others think ?

[Andrew Gabriel]

I think this is fine. However, I would only connect one of the earths to the 6mm cable's earth. I would run the other in a separate green/yellow single to the earthing terminal in the CU so there is no single failure point for the CPC. (It's good practice to wire the two ends of CPC in a ring to different earthing terminals too, so one loose screw won't lose you all the ring's earthing.)

[Grunff]

Ok, that seems like a good idea. Thanks.

Yup, I've done this throughout.

[Lurch]

On Mon, 03 May 2004 21:06:10 +0100, in uk.d-i-y Grunff strung together this:

I've done it many times before, not quite sure if it's strictly to the regs but the consensus of the group last time this was raised was yes, go ahead it's fine. And everyone I've worked with!

[BigWallop]

This sounds OK, but try to get a 45amp junction box and give yourself a bit more of a safety margin. You should also find it bit easier to get the cables into it.

[Grunff]

On the topic of junction boxes, anyone recommend a *good* make? The ones from Screwfix (and my local CEF, and B&Q, and Wickes) are very poor. I could carry on buying them from different suppliers until I find a good one, but a recommendation would be nice.

[usenet]

On the other hand it means all the numbering on the earth bar is wrong.

[Grunff]

There's numbering on the earth bar?!? ;-)

[Andrew Mawson]

Grunff,

I'm sure it'll work fine but I'm also sure it'll confuse people in the future. If you have to put in one junction box to do it 'your way' why not put one in each leg so inside the C.U. they are conventional and seperable if anyone has to do a loop impedance test.

Andrew Mawson

[Christian McArdle]

I'd crimp (and solder) two 2.5mm runs. This way, you know the connections will still be made in twenty years time, when the junction box is under your new stone/laminate/hardwood T&G floor.

Christian.

[Grunff]

How would you house your made connection(s)?

[Christian McArdle]

Heatshrink tubing then insulation tape.

Christian.

[Grunff]

Not box up in any way?

[Christian McArdle]

I wouldn't bother, unless there is a specific reason to do so, such as the likelihood of mechnical damage.

Christian.

[Lurch]

On 4 May 2004 08:41:11 GMT, in uk.d-i-y [e-mail] strung together this:

Renumber it then.

[Lurch]

On Tue, 04 May 2004 09:24:53 +0100, in uk.d-i-y Grunff strung together this:

The BG ones are pretty roomy, you'll easily get 2x2.5mm and a 6mm in them. They're Senates own brand, Sector or some other wholesalers stock them under the BG label.

[usenet]

On all three of the consumer units I've installed in the past couple of years the neutral bus bar and the earth bus bar both had numbers. I thus matched up the numbers used with the MCB positions for each cable as that seemed to be what was intended.

That's a Crabtree, a Denmans own brand and a n other whose brand I can't remember.