Unofficial earthing

Looking at someone's consumer unit the other day, as one does, I noticed
that the earth connection from the cu was to a clamp on the lead sheath
of the incoming supply cable. This arrangement has been in place for
many years, but was almost certainly done by a previous owner as an
unofficial, untested, modification.
This is in a pre-war house, in an urban area, with underground supply,
with a couple of inches of a lead sheath visible where it emerges from a
thickly-insulated supply cable. There is a single 30mA RCD protecting
all circuits, which apparently trips readily on any neutral (or,
presumably, phase) to earth short. There's equipotential bonding in
place to the incoming gas and water pipes, and supplementary bonding in
the bathroom. All wiring is around 20-30 years old, with some later
additions, but nothing older.
The owners asked me what they should do about the earthing: leave "well"
alone? Get something (what?) tested? Throw themselves at the mercy of
their supplier, and ask him to provide an earth? Treat it as TT (with
or without an extra earth rod? They're an elderly couple, and don't
really want massive disruption.
I said I'd ask here.
Reply to
Autolycus
Why don't you just Google for "electrician" and give them the number, surely they are not helpless! It might not be a modification. I have seen the arrangement you describe many times - often done by the local electricity company before privatisation. Why have they suddenly become concerned about the earthing arrangements? Don't go trying to scare people when you don't have a clue what you are talking about. Are you a salesman by any chance? You might do well in the double glazing industry!
Reply to
Pete Smith
Well, it confused me because that's how mine is done, with a braided strap and the house was built in 1955. Am I missing something ?
Andy.
Reply to
Andy Cap
In article , "Autolycus" writes:
I was waiting for the part where you decribed what what was wrong with the installation, but all you described was a normal TN-S installation. Why do they think anything is wrong?
Reply to
Andrew Gabriel
In article ,
Earthing to the cable sheath is still one of the approved methods where PME isn't available. And will still be provided by the supply company. It can be tested in the usual way.
Reply to
Dave Plowman (News)
On Thu, 31 Jan 2008 08:15:46 -0000 someone who may be "Autolycus" wrote this:-
Nothing wrong with this in theory. It is a standard method of earthing.
However, there may be problems in the details. If it is a "standard" clamp applied to a lead sheath, which is not reinforced with steel, then it is likely to be deforming the lead, making the clamp lose over time and perhaps crushing the paper insulated cores of the cable.
If you could take a photograph and put it somewhere publically accessible someone might be able to help more.
Reply to
David Hansen
Thanks for the comments so far.
Pete: Having a bad morning? The point about asking here was either to receive reassurance, or to be an informed buyer when asking an electrician who, particularly if found through random searching, may have his own agenda. The abuse didn't seem strictly necessary.
Andy: Yours may have been done professionally - the owners think the one I asked about may be an amateur job.
Andrew: I had remembered references to the distributor providing an earth - I wanted to check that it was OK for others to have provided it to the supplier's cable sheath. The OSG (4.9 (vi)) refers to the use of lead sheaths as earth electrodes for TT, with various conditions, and in 4.10 says that the supplier should be asked for advice about arrangements for connection for TN-S installations. The Installation Certificates shown in Appendix 7 only give two choices of box to tick for earthing arrangement - "Distributor's facility" or "Installation Earth Electrode" - hence my question about treating it as TT.
Dave P: As above - amateur as against supply company.
David H: I noticed the clamp was still tight, but with no apparent distortion of the sheath.
I think that the overall conclusion is that the method is reasonably sound, if not strictly compliant, but should perhaps have its earth electrode resistance checked.
Reply to
Autolycus
What's the reason for the belief that it is unofficial, untested, amateur, not strictly compliant etc?
Reply to
boltmail
In an earlier contribution to this discussion,
Why don't you take a photo of it, upload it somewhere, and post a reference to it here? We'll all know what you're talking about then!
Reply to
Roger Mills

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