moving and enlarging consumer unit

[Fred]

Hi,

I think I am going to need a bigger consumer unit. There are no spaces for expansion and I think I might need to add a new radial when I buy the new induction hob (which will be 7.2kW).

The consumer unit is a Crabtree. I used google to see what options Crabtree offered and I found this image:

It's not unlike mine in that inside is a complete mess of wires. Are they supposed to be like that? As the neutrals go to one side and the earths go to another, I suppose you can't help the wires crossing but are they supposed to be that messy?

The only other one I have ever seen is Andrew's that gets posted here and it looks so much neater!

What should I do? Should I replace my consumer unit with one larger consumer unit or should I keep the CU that I have and buy a second, smaller CU and have two consumer units? Buying a second, smaller CU might be cheaper but would use up more wall space. Perhaps having two CUs would allow me to have lights in one and sockets inthe other, or divide the circuits some other way, which might be a good thing if one box goes out of service (but how often does that happen)?

The reason I ask is that the photo seems to be part of a discussion on a web forum and part of that discussion is whether the electrician should have used one consumer unit or two.

I would also like to move the CU to somewhere more accessible. I was unsure about extending the cables but using a din rail as in Andrew's picture looks a neat way of doing it. I have not used din rails before so I am unsure what I would need to buy to do this. Would I need something like this:

The photo shows metal exposed at the sides; is that right? I was expecting it to be enclosed to prevent shocks, short circuits, etc.

TIA

[Tim Watts]

On Sunday 23 June 2013 12:15 Fred wrote in uk.d-i-y:

buff/dp/CN12730

There are a lot of DIN terminal types. The RS own brand are not bad.

What matters is that the current rating is enough and the terminals are suitable for the wire. In both cases your link above passes for upto 4mm2 and 27A.

Some terminals are open on one side to keep the thickness down. It will be shielded by the next terminal and the last one needs a blanking piece that will be on sale for that particular terminal.

Some terminals also accept strapping bars to form banks of common terminals but you will not need them for this application.

Colour coded terminals can make wiring a little easier - at least for the earths but not essential as the way Andrew uses them you only have to check outgoing wire colour with the incoming to avoid gratituous mistakes.

[Vir Campestris]

... and you might not. Ours is happily sharing a circuit with the electric oven. Apparently diversity regs mean you can do this. And to be honest, they're right - it's unlikely that both ovens and all four rings will be on ful at once, and for any length of time.

Andy

[Fred]

Thanks all.

You are quite right to remind me about diversity. At the moment the old hob and oven are next to each other and connected to one 6mm^2 radial protected by a 32A MCB.

I don't know the rating of the old hob but the new one will be 7.2kW and the oven is 4.2kW. I was just adding the two together to make

11.4kW and thinking this was too much for 6mm^2 T&E. I was thinking of moving the oven to a different place and having two separate radials in 6mm^2 and was going to use 40A mcb.

The diy wiki has reminded me that diversity is 10A plus 30% of the remainder for cookers, so that makes the load about 22A, so there would be no need to upgrade the 6mm^2 to 10mm^2 cable and no need to upgrade the mcb to 40A.

I think the CU will eventually be moved to somewhere more accessible so using the DIN terminals to extend the cables and replacing the CU with one with room for expansion can't be a bad thing when that time comes.