Numbering of circuits in Consumer Unit

[Mike Hall]

I've just bought a new Wylex split load consumer unit:

The unit has the main incoming switch on the right hand side, and the RCD half way along.

The kit comes with some useful labels, ("1", "2", "3" etc) for numbering the MCB circuits, however I don't know if conventionally these should be numbered left to right or right to left, (ie. Number 1 nearest to incomer, or Number 1 nearest to LHS).

If it's any clue, then inside the CU, the terminals of the earth bus bar are numbered 1-13 in a left to right sense, and the terminals of the two neutral bus bars are numbered 1-7 in a *right to left* sense. Obviously I'd like to get all my "1"'s and "2"'s the same throughout just to try and make fault finding easier for the next encumbant. Can anyone advise what is the norm .... ?

[John Rumm]

Personally I like labels that say things like "Upstairs Lights", or "Downstairs Ring" etc. eliminates all the guess work!

[Chris Oates]

particularly good idea as when allocating circuits your highest rated load must be in the first position after the switch - this means (1) right to left.

[Andrew Gabriel]

I had something like that in a 10 year old house. What you had to remember in this case was that the MCB labelled "Upstairs Lights" did the downstairs lights, and the one labelled "Downstairs lights" did the upstairs Lights" ;-) I think the ring circuit MCB's were similarly transposed, but I could never remember for sure so I just ignored the labels...

[usenet]

Our house was even better, when we arrived the two ring mains had

*one* end of each transposed so you had to turn off both MCBs to actually remove the power (not to mention that you had to trip two 32 amp MCBs in parallel to clear a fault).

[Lurch]

Not has to be, just usually is.

SJW A.C.S. Ltd.

[Lurch]

If you're doing it to the regulations then all numbering must correspond throughout. i.e. Circuit 1, N in 1 on neutral bar, E in 1 on earth bar, L to MCB no.1 etc... I have wired panel boards the size of your garage door with cables the size of your arm and they don't always go where you want so you just re-number everything to correspond. It's all safe and correct as long as it's labelled.

SJW A.C.S. Ltd.

[Mike Hall]

Thanks to everyones tips I've now installed my new consumer unit, and as an added bonus most of the cables managed to reach the new unit and so didn't need extending. Those cables that didn't reach are still being fed from the old CU which is in turn being fed from an MCB on the new CU, (as a temporary solution). Installing the new 25mm^2 tails was a barrel of laughs, and here's a tip for fixing them to the wall- 15mm pipe clips make a good substitute for cable clips if you happen to have some lying around, (although they are a fraction on the large side).

A couple of quick questions have arrisen since this migration:

The kitchen ring circuit had three wires attached in the (old) consumer unit. Chasing this out it seems that there is a 'standard' ring and an additional circuit feeding only one double socket, (also in the kitchen). Am I right in thinking that this is in fact OK - the lone socket is simply classed as a spur, but rather than being taken from an existing socket or from a junction box it is taken direct from the CU? (AFAIK there are no other spurs on the ring, so it is well below the requesite spur/socket ratio).

Secondly, one of the other existing circuits looked to be wired in fairly new cable, but when I came to strip the live conductor I had a hell of a job removing the insulation. - I was only trying to remove

10mm of insulation to fit into a terminal, but it seemed like the insulation had become stuck to the copper. Has anyone encountered this before? - Is it just cheap cable, or is it a sign that the cable has overheated in the past?

Oh, and in case anyone was wondering about my original left to right or right to left question, it all became apparent.... When I wrote the original post I was staring into the inards of the CU - of course when I put the the cover back onto the unit the MCB slots were already numbered on the outside of the case!! - Doh! (Right to left by way).

[stefek.zaba]

Yes, that's just what it is - a spur off the ring. Depending on just how long the run to the kitchen is, though, there's an outside chance that it's below spec in earth impedance for a 30A/32A breaker, and also an outside chance that the cable run passes through bits of thermal insulation or bunched with other cables such that a 30A/32A breaker is a bit above best practice for a 2.5mmsq cable. It's unlikely that any of these gotchas apply in practice, though.

Still, if you have a dedicated bit of 2.5mmsq running from CU to kitchen, it mught be an ideal wire to use for a dedicated fridge-and- freezer circuit, on the non-RCD side of your CU: then you could give it its own 20A MCB, and wiring it as a radial gives you as many sockets or FCUs as you like. Pernickity types might want to use non-standard plugs and sockets for this radial (you can, f'r example, get 13A plugs and sockets that are 'nearly normal' but have the earth pin horizontal rather than vertical), to comply with the absolute letter of 'sockets which might reasonably be used to supply portable equipment outside the house should be protected by a 30mA RCD'; me, I'd be happy with indelible labelling - "FRIDGE/FREEZER ONLY".

Could be the latter. Presuming the bit you were stripping was right by the end which had been connected into the MCB/fuseway on the old CU, it could be as simple as the screw not having been tightened up too well when it was installed; a marginal contact like that would account for the insulation getting over warm just at the end. What does this circuit feed?

Stefek

[Mike Hall]

This spur just passes through the wall, ie the socket is virtually on the back of the CU. (1m cable max). No grouping or thermal insulation issues at all either, so I'm happy.

That's what I was hoping for, but it's on the wrong side of the kitchen unfortunately.

I think I chopped off a good 50mm. I can't remember exactly what this circuit fed, (and I'm currently at work), but it was definitely sockets, (as opposed to any fixed equipment). The whole of the sockets arrangement needs a good looking at though, as at the moment it seems like there are several spurs that were all fused at 30A in the old CU. Just in the process of planning and deciding whether I should stick with the current spur arrangement, (adjusting protected values where appropriate), or whether I should start again and set up rings. I'm guessing that the spurs were originally installed due to concrete floors downstairs, and all power therefore funning under first floor, however at least some of the wiring is original 1950's and so needs replacing. So far I've replaced the upstairs lighting, (which went incredibly smoothly), but am just delaying pulling up the floorboards .... for the moment!