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 .... ?
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...
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).
On 22 Jan 2004 02:36:04 -0800, mike firstname.lastname@example.org
(Mike Hall) wrote:
If you're doing it to the regulations then all numbering must
i.e. Circuit 1, N in 1 on neutral bar, E in 1 on earth bar, L to MCB
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.
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
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).
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
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
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!
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