New consumer unit but with complications

[bloxy]

OK Tell me the worst.

I have a 1970s house, the consumer unit is an old brown 6 way Wylex, the rewirables have been replaced with plugin MCBs many years ago. The wooden frame part of the unit is falling apart, it needs replacing.

Now the complications. The CU is in an outside meter box which is let into the external skin of the lounge wall on the side of the house. The Service cable enters through a bashed out hole in the bottom of the meter box via the wall cavity. The service head has a little label by it saying PME System but it is definitely TT with earth rod not PME.

There is no Main Bonding (due to v_ELCB) but bathroom does have cross bonding of pipes and radiators which goes back to CU earth.

The DNO recently installed one of the new mini meters. The meter tails goto a v-ELCB (I know it's obsolete) thence to the CU, 2 ring mains, 2 lighting, 1 cooker, 1 immersion. The cables from the CU go up inside the cavity (no insulation) to first floor and loft. I also know there are junction boxes under floors which are inaccessible.(solid wood floors on top). I know this is all Part P.

So if and when I get a certified professional in to replace the CU and v-ELCB what else will be involved in view of existing circuits in cavity and CU in the meter cabinet?

 

[flameport]

Supply type - if PME is available then this should be used in preference to the TT/earth rod. This will need to be confirmed with the DNO (electricity company responsible for the supply network in your area). The network may have been upgraded to PME after the property was built.

Main bonding will need to be installed, from the CU to the gas, water and any other metallic services. The voltage ELCB will be removed.

Cables in the cavity - ideally these should be moved although they could be left there. You won't be able to have cavity wall insulation fitted while they are still in the cavity.

Junction boxes under the floor - again these should be accessible, and ideally would be removed completely. As with the cavity cables, it is not compulsory to move them.

Most DNOs do not allow other equipment in the meter cabinet, so fitting the new CU in there could be a problem - check with the DNO on that one as well.

Other work may be required depending on the condition of the existing wiring and sockets etc., although if 1970s, it should still be in good condition.

 

[bloxy]

I am aware of junction boxes being accessible. I did check them to make sure the connections were good before I laid the flooring but taking them out would now be a major problem so glad it's not compulsory.

The DNO has changed the meter twice and the service head once in the last ten years and never questioned the CU in the meter box but I realise that may be different when it comes to replacing it, trouble is where else can it go? There is nowhere on the wall inside as it is the lounge wall, the garage is on the other side of the house (goodness knows why they didn't put it there in the first place).

We are on overhead supply in the village (mine comes off the pole and under ground into the meter box, does this make PME unlikely?

I have seen most of the wiring when I have had floorboards up for plumbing and speaker cabling etc and it looks in good condition.

From reading these forums I have a decent idea of what is available and what is now required in the 17th edition but I am looking for information so I am in a position to understand what I may be quoted for.

So assuming the cables are left as they are and it's just a CU change and the six circuits are kept as they are, would it just be a 7 way RCD CU (as there isn't going to be room for anything bigger in the meter box) but does it have to be a split board? What about individual RCBOs? What can I expect to be quoted?

Any information gratefully received.

 

[RF Lighting]

Not certain about your area, but certainly round where I am (YEDL area), PME is availible on most of the rural network these days.

You say you recently had the head replaced, and there is a PME sticker on it, so I'd think it probably is available, but it has not been used so far.

It is much more preferable to a TT supply (IMO anyway)

 

[bloxy]

The head was replaced at the first meter change 5-10 yrs ago, this was then changed to the new mini meter a few months ago. The PME sticker I think is original, it was certainly there when we moved in 23 yrs ago! and we were TT then as now (no earth from the head).

From my reading I know PME would be a better option (though I believe you can get a perfectly good earth from TT), is there an easy way to find out if it is available in my area?

Our supplier is Atlantic but the DNO is EON Central Networks.

 

[flameport]

If you get a board with RCDs, you will need at least 2 of them, a single RCD for the whole installation is not compliant.
A much better option is individual RCBOs for each circuit, this will also make the board significantly smaller.

As for price, this depends on where you are and how much other work is involved, but to supply and fit a new CU of the size you describe, £350 upwards.

How close are the gas/water services to the electricity cabinet?

 

[333rocky333]

Skeleton boards are sometimes used in these enclosures.

http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Skeleton_Consumer_Units/index.html

 

[bloxy]

How close are the gas/water services to the electricity cabinet?

No Gas, the water main enters the kitchen on the opposite corner of the house. The main bonding will have to run externally around the back and up the side of the house, about 30m.

I thought RCBOs would be the likely way to go.

 

[properleckie]

Agree with what has been said, plus if meter co has problem with CU in 'their' box and cables all go up cavity, can you put second box above theirs divert wiring into new all rcd/rcbo CU with tails between boxes?
I have just done this where room with CU in behind meter box was changed to a bathroom, at least plenty of spare cable to work with.
Not pretty but if not on front of house could be a way out.

 

[bloxy]

I did wonder about a second box and that could be surface mounted (don't want to hack another hole out of the outer skin)? But as I said DNO has changed the meter twice and nothing has ever been said about CU in box.

As I understand it it is my box they just put the meter in it. Plus the new meter is smaller than my Central Heating programmer(last meter was a large digital display one, miss the spinning disk that was in the original kept me amused for hours ) and with the v-ELCB gone we will have more space in there, just a constraint on the width of a new CU because of the size of the box.

I feel happier now about getting someone in to look at it knowing it shouldn't involve major rewiring.