Spoke to Soon :-(

Eon sent their contractor to change the cut-out, which he completed
with the added bonus of checking the Earth Loop imp (0.26 ohms) so
now
I don't have to use the default value of 0.8 when I'm calculating it
for the ccts.
Now the not so good:----
I asked him about providing a better clamp on the earth sheath of
the
cable ready for when I need to connect my new 16mm earth tail.
(The existing one is small and only has a 4mm earth tail) He said he
couldn't do that and
that I would be better off applying for a PME.. I pointed out that a
PME would cost me £70 and since I have a TN-S supply with a perfectly
good earth why should I spend £70 instead of Eon making proper
provission for a 16mm earth tail.


your views appreciated ....


Andy

ac1951 wrote:

I asked him about providing a better clamp on the earth sheath of the
cable ready for when I need to connect my new 16mm earth tail.

You aren't supposed to connect _your_ earthing conductor to _their_
cable. _They_ connect _your_ earth wire. Usually you present a 16 mm^2
earth along with the meter tails and they will connect it to the cable
sheath or to the sealed PME terminal, as appropriate. In this case you
should probably have mounted an earth block near the isolator position
and left a short length of 16 mm^2 attached and he might have connected
it - but too late for that now.

You could ask explicitly whether they'd come back and connect a TN-S
earth. If not the only options are to take up the PME conversion offer
(£70 doesn't sound too bad), or to sink your own earth electrode and go
for TT. With everything needing 30 mA protection anyway under the 17th
ed. (unless you use special cables), TT could be the cheaper option -
but beware that it rules out using a metal CU, unless the manufacturer
offers an 'RCD insulation kit' or some such, to achieve Class 2
insulation on the live incoming tails ahead of the RCDs.

Don't be tempted to make your own TN-S earth connection using a BS 951
earthing clamp. There's a known risk of squashing the old lead sheathed
cable and making a big bang. Yes I know the old electricity boards and
RECs used to use them, and still sometimes re-use them, but it's a
deprecated practice now. If they do it it's at their risk, but if you
blow their cable up ...

--
Andy

Don't be tempted to make your own TN-S earth connection using a BS 951
earthing clamp. There's a known risk of squashing the old lead sheathed
cable and making a big bang. Yes I know the old electricity boards and
RECs used to use them, and still sometimes re-use them, but it's a
deprecated practice now. If they do it it's at their risk,


but if you
blow their cable up ...

Anyone done that?.. Bloody great big bang or does it arc and burn and
either burn itself out and/or take the substation transformer fuse with
it?..
--
Tony Sayer

tony sayer coughed up some electrons that declared:

Don't be tempted to make your own TN-S earth connection using a BS 951
earthing clamp. There's a known risk of squashing the old lead sheathed
cable and making a big bang. Yes I know the old electricity boards and
RECs used to use them, and still sometimes re-use them, but it's a
deprecated practice now. If they do it it's at their risk,


but if you
blow their cable up ...

Anyone done that?.. Bloody great big bang or does it arc and burn and
either burn itself out and/or take the substation transformer fuse with
it?..

From the stories my late father told me (ex LEB), assuming a short happens,
it will most likely be a *bloody* big bang, followed by a section of cable
around the fault disappearing, followed by your mate dialling 999 because
the plasma from the ex-cable section had an argument with your face.
Typical dead-short fault currents at that point are likely to be measured
in many kA. This all changes if the installation is rural on the end of a
bit of string and a weedy transformer on a pole, but it would still be
unwise to invite trouble.

My father was been consigned to hospital for a fair time back in the late
50's due to an substation breaker exploding on him. He met many co-victims
of electrial burns.

I found the medical photos when clearing out his house. The results really
weren't pretty. To be fair, his injuries were exasperated by the breaker's
arc quenching oil going up, but plasma burns can still be pretty horrific.

As to the breaker at the substation, for a typical urban substation,
probably not. As for the fuse in the link box down the road (depending on
the REC and system), maybe, maybe not. 300A fuses were used in London 30
years ago, no idea what they use now.

The real problem with old cable is that some of it is paper/oil insulated
and over time, the oil can drain and dry out of the end section leaving the
paper brittle and prone to failure by the slightest disturbance which
includes fiddling with earth clamps, bending or otherwise crushing the
cable.

Cheers

Tim

Tim S wrote:

As to the breaker at the substation, for a typical urban substation,
probably not. As for the fuse in the link box down the road (depending on
the REC and system), maybe, maybe not. 300A fuses were used in London 30
years ago, no idea what they use now.

Yes, the fuse is likely to be in a link box or distribution pillar - 300
or 500 A in my limited experience of such things.

--
Andy

On Tue, 17 Jun 2008 01:39:10 +0100 someone who may be Andy Wade
wrote this:-

Don't be tempted to make your own TN-S earth connection using a BS 951
earthing clamp. There's a known risk of squashing the old lead sheathed
cable and making a big bang. Yes I know the old electricity boards and
RECs used to use them, and still sometimes re-use them, but it's a
deprecated practice now.

Depending on cable type the lead sheath should be covered with steel
reinforcing wire, assuming it was terminated properly.

Obviously putting a standard earthing clamp directly on the lead
sheath of a cable is likely to end in tears.




--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54

In article ,
tony sayer writes:
Don't be tempted to make your own TN-S earth connection using a BS 951
earthing clamp. There's a known risk of squashing the old lead sheathed
cable and making a big bang. Yes I know the old electricity boards and
RECs used to use them, and still sometimes re-use them, but it's a
deprecated practice now. If they do it it's at their risk,


but if you
blow their cable up ...

Anyone done that?.. Bloody great big bang or does it arc and burn and
either burn itself out and/or take the substation transformer fuse with
it?..

It happened in the Kentucky Fried Chicken in Dunstable a few
years ago. The resulting smoke damage closed the place for
some time, but unfortunately, it did eventually reopen...

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

Andy Wade wrote:
ac1951 wrote:

I asked him about providing a better clamp on the earth sheath of the
cable ready for when I need to connect my new 16mm earth tail.

You aren't supposed to connect _your_ earthing conductor to _their_
cable. _They_ connect _your_ earth wire. Usually you present a 16 mm^2
earth along with the meter tails and they will connect it to the cable
sheath or to the sealed PME terminal, as appropriate. In this case you
should probably have mounted an earth block near the isolator position
and left a short length of 16 mm^2 attached and he might have connected
it - but too late for that now.

Met and interesting one the other day. A mate needed some minor
electrical work done, and asked me to have a look at the existing setup
to see if there was anything else that needed doing. I figured the main
EQ bonds may need attention, and so had a look at the head end. It
revealed a TN-S system with 10mm^2 earth single connecting an earth
block to the cable sheath. The sheath seemed to have a steel pipe
appended to the end of it, and a bog standard BS 951 earth clamp wrapped
round it. The thing that caught the attention was that single wire was
the only thing connected to the earth block. The CU wasn't!

Investigation with a loop tester did however reveal a decent enough
impedance of about 0.22 ohms.

After a bit of hunting about we eventually found a bare stranded single
running from the CU into a metal box used to terminate some conduit (old
wylex insulated fuse board), from there it ran hidden behind a bit of
conduit (odd wiring - done in the 60's, some in PVC Twin (but not always
with E), and some in steel conduit) disappearing under the floor.
Eventually found it connected to the lead incoming water main somewhere
under the floor.

Don't be tempted to make your own TN-S earth connection using a BS 951
earthing clamp. There's a known risk of squashing the old lead sheathed
cable and making a big bang. Yes I know the old electricity boards and

Indeed, I am nervous enough making a clamped connection to a lead water
pipe... at least all that happens there if you break it is you get wet!

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Current 4mm earth wire is attached to cable sheath using a shell clamp
that is obviously designed to meet the outside diameter of the sheath.
Looking at it I could crimp or solder a 16mm lug (standard lug comes
6mm hole) onto the earth tail and attach this to one of the shell
clamp bolts.

Thought I would call Eon and asked them to send someone to carry out
the work ;-)
They said, earthing is your responsibility and whilst there may
currently be an earth provided via the cable sheath we offer no
gaurantee that this is adequate. The only earth service we now offer
is PME and if that cannot be delivered you have to make your own
arrangements.
With regard to the PME we will only make it available and you will
have to get your own electrical contractor to make the connection onto
it.

So, looks like I'm about to kiss goodbye to £75.