Am looking into replacing an antique fuse box with a split load
Contactum consumer unit - in part to provide a modern ring circuit.
But a survey of the current installation indicates potential earthing
problemss, so help please!

By way of background the supply is PME - upgraded (new supply cable,
meters etc etc) around 1995-98 from TT(?) after a fault, by the
successors(?) of SEEBOARD.

The incoming supply cable looks quite beefy. It supplies a largish
house plus several small flats via switchgear leading off in parallel
to the main house switchgear (everything goes through the same elec
board meter & cutout). Can only guess as to the incoming supply cable
size, but the cable from the board cutout is 16.3mm diameter overall
(including the brown insulation/sheath), which suggests something
around 70mmsq to 100mmsq depending on the sheath/insulation thickness.
Can anyone identify this size more exactly please?

There's quite a lot of switch gear attached, one of which is a 60A
switch fuse leading to the antique fuse box in question. It is hoped
to leave this switch & the cable (imperial?? - around 25mmsq) to the
antique fuse box in place as it looks healthy. However the earthing
is via steel conduit & looks to require upgrading to a proper 'modern'
copper earth cable.

The yellow/green insulated multi-strand earth-to-water bonding cable
appears to be at least 25mmsq. It has crimped lugs so it isn't easy
to measure directly: the overall diameter (including the yellow/green
pvc insulation) is 10.4mm and it is multi-stranded - perhaps 15+
strands. I can't get an exact fix on the size of the strands, but
they are perhaps 2-2.5mm in dia. Please, can anyone identify the
exact size/spec of this cable?

This is way over the 'typical' sizes shown for PME on page 28 of the
IEE On-Site Guide. Then looking at table 10a on page 161 gives a
wider picture, and it all rather implies the supply must be 70mm^2 (or
larger?).

So what size should the new earth bonding cable from the supply earth
point to the new Consumer Unit be? Any opinions/advice will be most
gratefully received.

If the supply cable is really 70mmsq then am I reading On-Site Guide
table 10a (pg 161) correctly that a 35mmsq earth cable should be
specified for the run earth terminal-to-Consumer Unit? Or should it
be sized according to the 25mmsq cable coming from the switch-fuse
(16mmsq if I read pg 161 aright)?

BTW I enquired about 25mm^2 earth cable at a TLC branch only to be
greeted with astonishment, so if a heavy guage earth cable turns out
to be needed, where can you buy it?

many thanks

In article ,
jim_in_sussex wrote:
BTW I enquired about 25mm^2 earth cable at a TLC branch only to be
greeted with astonishment, so if a heavy guage earth cable turns out
to be needed, where can you buy it?

Dunno why they should be astonished - it's in their cat, CA25S at 1.20 per
metre. If it was uncommon, they wouldn't offer cut lengths.

--
*Taxation WITH representation ain't much fun, either.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)" wrote in message ...
In article ,
jim_in_sussex wrote:
BTW I enquired about 25mm^2 earth cable at a TLC branch only to be
greeted with astonishment, so if a heavy guage earth cable turns out
to be needed, where can you buy it?

Dunno why they should be astonished - it's in their cat, CA25S at 1.20 per
metre.

I was astonished that the sales clerk was astonished as I was reading
from the catalogue! He knows a lot about elec wiring & said he hadn't
sold any 25mmsq in yonks, but could proably get it in.

Poking about it rather appears that TLC is more of a buying
organisation or cooperative & individual outlets are fully or
semi-independant. Also TLC deals mainly with domestic sized gear, so
to be fair it is quite understandable.

If it was uncommon, they wouldn't offer cut lengths.

Yes cut is in the catalogue, but the mail order operation seems to be
run from the centre, not from the shops.

In article ,
jim_in_sussex wrote:
Poking about it rather appears that TLC is more of a buying
organisation or cooperative & individual outlets are fully or
semi-independant. Also TLC deals mainly with domestic sized gear, so
to be fair it is quite understandable.

Think they actually stock about the same range as most ordinary
wholesalers. And are rather better than some. But you can't expect every
branch to stock the entire range - same really as anywhere.

If it was uncommon, they wouldn't offer cut lengths.

Yes cut is in the catalogue, but the mail order operation seems to be
run from the centre, not from the shops.

Well, yes. But the shops will get in anything you need from 'head office'
pretty quickly.

--
*Succeed, in spite of management *

Dave Plowman London SW
To e-mail, change noise into sound.

Yes cut is in the catalogue, but the mail order operation seems to be
run from the centre, not from the shops.

I've ordered over the internet and the order was definitely dealt with by
the local branch and came in a TLC branded van, not via Courier.

Christian.

In article ,
Christian McArdle wrote:
Yes cut is in the catalogue, but the mail order operation seems to be
run from the centre, not from the shops.

I've ordered over the internet and the order was definitely dealt with by
the local branch and came in a TLC branded van, not via Courier.

It must depend on where you are, given that TLC aren't nationwide. Yet.

--
*I'm pretty sure that sex is better than logic, but I can't prove it.

Dave Plowman London SW
To e-mail, change noise into sound.