wrote in message
...
Hello,

I have the electric meter in a box outside. The tails then come inside
under the stairs and across the room to the fuse box in the corner. I
don't like having this long stretch of permanently live cable. I'm
upgrading the fuse box and thought that where the tails enter the
house I could fit a 100A incomer in something like this:

http://www.screwfix.com/app/sfd/cat/...74436&ts=49777

and then I could always isolate the section of tails between the
incomer and the fuse box. Does this sound like a good idea?

Can you recommend any other good enclosure for an incomer? I can only
find consumer units with a number of spaces in and I really only need
a 2 way box for the incomer. The Wylex does not come with any cut outs
or grommets, etc. what would I need to buy to use with this?

Thanks.

What you have is normally not allowed as meter tails are usually limited to
3m or some such. What you should have is exactly what you propose, which is
called a sub-main. The suppliers do not like protecting long runs of heavy
cable inside a property with the supply fuse and require you do do, and be
responsible for, your own protection. The box you refer to is IP65 rated for
use outside (so has no cutouts). You can get small enclosures for DIN rail
stuff but you may have to go to an electrical supplier.

Disclaimer: "Doing any of this work yourself without proper qualification or
inspection will undoubtedly be in contravention of part P etc., and I am
obliged to suggest you don't".


--
Bob Mannix
(anti-spam is as easy as 1-2-3 - not)

Bob Mannix wrote:

What you have is normally not allowed as meter tails are usually limited to
3m or some such. What you should have is exactly what you propose,

The proposal was for "an incomer," which is rather vague. If the
circuit length between the mater and the consumer unit exceeds the
maximum allowed for meter tails (3 m, or less in some areas) a
switch-fuse will be needed.

For 60 or 80 A supplies the MEM 800KMF
http://www.mem250.com/products/produ...uctcode=800KMF
is popular with electricians for this job. Alternatives are the Wylex
108 or 108M units
http://www.tlc-direct.co.uk/Main_Ind...P_1/index.html
or the 110M for 100 amp supplies
http://www.tlc-direct.co.uk/Main_Ind...d_N/index.html.

which is called a sub-main.

Actually it's a distribution circuit. It only becomes a submain if it
goes to a separate building (e.g. to a detached outbuilding).

Remember that the main equipotential bonding must be connected to the
main earth terminal at the origin of the installation. It is
permissible for the bonding to be made at the consumer unit but then the
earth conductor of the distribution circuit acts as both circuit
protective conductor and main bonding conductor and must be sized for
the more onerous of those two requirements. For 25mm^2 tails that means
that a 16 mm^2 earth will be needed, if copper, or 36.1 mm^2 for steel
armour (so the armour of 2-core 25 mm^2 SWA (= 60mm^2) is OK). However
16 mm^2 T&E could not be used without running a separate 16 mm^2
protective conductor.

Disclaimer: "Doing any of this work yourself without proper qualification or
inspection will undoubtedly be in contravention of part P etc., and I am
obliged to suggest you don't".

Building notice required, and that should trigger an inspection.

--
Andy

On Mon, 8 Jan 2007 18:05:38 UTC, wrote:

On Mon, 08 Jan 2007 14:21:10 +0000, Andy Wade
wrote:

For 60 or 80 A supplies the MEM 800KMF
http://www.mem250.com/products/produ...uctcode=800KMF
is popular with electricians for this job. Alternatives are the Wylex
108 or 108M units
http://www.tlc-direct.co.uk/Main_Ind...P_1/index.html


I was thinking a small enclosure with an 80A incomer would be cheaper
than these. Why is the switchgear so much more expensive?

It's a switch fuse, not a switch (to put it simply).

Andy was concerned that the length of the meter tails was such that you
really ought to have protection for those tails in their own right. All
that protects them at the moment is the supply fuse. If you fit a basic
incomer then there is no fuse included.

If the tails are less than 3m, you could use an incomer, but it would be
better to use a switch fuse.

Go to www.cpc.co.uk and look at:

PL02545

then fit a standard incomer. That's what I did.
--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
http://www.diybanter.com

On Mon, 8 Jan 2007 20:29:02 UTC, wrote:

On 8 Jan 2007 19:39:36 GMT, "Bob Eager" wrote:

I was thinking a small enclosure with an 80A incomer would be cheaper
than these. Why is the switchgear so much more expensive?

It's a switch fuse, not a switch (to put it simply).

Andy was concerned that the length of the meter tails was such that you
really ought to have protection for those tails in their own right. All
that protects them at the moment is the supply fuse. If you fit a basic
incomer then there is no fuse included.

If the tails are less than 3m, you could use an incomer, but it would be
better to use a switch fuse.

Go to www.cpc.co.uk and look at:

PL02545

then fit a standard incomer. That's what I did.


I agree with Andy that there should be some protection; that's why I
want to add "something" between the meter and consumer unit.

by 'protection', I (and I suspect Andy) mean some kind of fuse or
something that will break the circuit should damage or fault occur to
those long tails. All you have at present is the supply fuse.

The tails are roughly 3m; perhaps slightly over but no more than 4m.
Like I said they were added when the rules were different in the 70's.
Since moving in I have been concerned that this a run of cable is
permanently live. I think it unlikely that I would ever drill through
it, but I'd like to be able to isolate it in case something terrible
happens.

Isolation doesn't protect; after all, it might be an accidental damage
that you couldn't foresee.

So as the consumer unit is about to be upgraded, now seems to be the
right time to do something about those tails. I am puzzled though
about protecting long tails with a separate fuse. If there's a 100A
fuse at the meter, what good would another fuse at the switch be? Or
is it that the second fuse is slightly lower rated at 80A, which stops
the tails from melting?

Yes, essentially. I doubt the supply fuse would go at 100A, anyway. And
it's a damn sight more inconvenient.

--
The information contained in this post is copyright the
poster, and specifically may not be published in, or used by
http://www.diybanter.com

wrote:

I am puzzled though about protecting long tails with a separate fuse.
If there's a 100A fuse at the meter, what good would another fuse at
the switch be? Or is it that the second fuse is slightly lower rated
at 80A, which stops the tails from melting?

It's about the wiring regulations and demarcation of design
responsibility, rather than technical considerations alone. The DNO's
fuse is there to protect their equipment, not to protect parts of your
installation. The wiring regs (BS 7671) require you to provide
overcurrent protection as near as practicable to the origin of your
installation. It is accepted by the supply industry that you can rely
on the DNO's fuse to perform this role if and only if the tails are
short, i.e. 3 m, or such other shorter length that they may care to
specify.

Yes you will find older installations where this rule has been violated.
I don't think it was any different in the 70s, there was just rather
less enforcement then than now. If you are notifying this for Part P
then you can expect it not to pass inspection if the tails are 3 m and
you haven't provided an OPD.

DNO = distribution network operator, formerly known as REC or
electricity board.

OPD = overcurrent protective device, i.e. fuse or circuit breaker.

--
Andy