Mains power connection: mysterious black substance

5 views
Skip to first unread message

Jonelle

unread,
Jun 27, 2008, 2:29:31 PM6/27/08
to
Hi all

Background:
We recently had new CH installed. It required an electrician to come and
do the controls wiring. He looked in the cupboard housing our Consumer
Unit and mains connection, said the earthing was wrong, and fitted a new
earthing system (connecting CU, gas, etc all to the mains water in-pipe
under the sink). (He has charged £79 labour and £13 parts for doing
this; £109 inc VAT) (The CU and gas were previously earthed to a proper
earthing stake, hammered 2' into the ground under the cupboard, by me,
15 years ago: he said he wasn't "getting a reading" from this.)

Question:
Having done this, the guy pointed out to my wife (I was at work the
whole time he was here, else I'd have quizzed him a bit) that a black
substance was oozing out of the mains cable, at the point where it joins
the electricity supplier's fuse box (can't provide a picture sorry).

This stuff, which looks like tar, is solid, and cold; however it has the
appearance of "flowing", and indeed it's already flowed over the
earthing strap that the electrician fitted, three weeks ago. It's either
coming out of the cable pipe (it's the one about 1" wide, up through the
ground) or from the box it connects to (which precedes the actual mains
fuse box, before that connects to the CU).

I had never noticed this stuff before (ever, in the 22 years we've been
here). It could have been there for years, or ... maybe it started when
the electrician was working there?

The electrician said that it was the wrong side of the fuse box for him
to do anything about it, but "we might want to get the Supplier" to look
at it.

I'm wary of doing that, because they are absolutely bound to find
something wrong (now, aren't they?!) and we'll end up with a bill at
least as big as the CH (£2800) to have the place "properly" rewired.
(Maybe the electrician was hoping he'd get the job!)

We rewired the house 15 years ago: I did most of the work, but was
advised by a competent electrician from my place of work.

Any thoughts, anyone?

Cheers
John

Andrew Gabriel

unread,
Jun 27, 2008, 2:37:42 PM6/27/08
to
In article <lalaw44-548B74...@plusnet.vsrv-ams.supernews.net>,

Jonelle <lal...@hotmail.com> writes:
> Hi all
>
> Background:
> We recently had new CH installed. It required an electrician to come and
> do the controls wiring. He looked in the cupboard housing our Consumer
> Unit and mains connection, said the earthing was wrong, and fitted a new
> earthing system (connecting CU, gas, etc all to the mains water in-pipe
> under the sink). (He has charged £79 labour and £13 parts for doing
> this; £109 inc VAT) (The CU and gas were previously earthed to a proper
> earthing stake, hammered 2' into the ground under the cupboard, by me,
> 15 years ago: he said he wasn't "getting a reading" from this.)
>
> Question:
> Having done this, the guy pointed out to my wife (I was at work the
> whole time he was here, else I'd have quizzed him a bit) that a black
> substance was oozing out of the mains cable, at the point where it joins
> the electricity supplier's fuse box (can't provide a picture sorry).
>
> This stuff, which looks like tar, is solid, and cold; however it has the
> appearance of "flowing", and indeed it's already flowed over the
> earthing strap that the electrician fitted, three weeks ago. It's either
> coming out of the cable pipe (it's the one about 1" wide, up through the
> ground) or from the box it connects to (which precedes the actual mains
> fuse box, before that connects to the CU).

It's pitch, which was often used to fill (and hence waterproof)
old mains connection boxes. Is the box (or whatever) it's coming
from warm or hot? That would speed it up.

You might want to read up on the Pitch Drop Experiment:
http://www.physics.uq.edu.au/pitchdrop/pitchdrop.shtml

> I had never noticed this stuff before (ever, in the 22 years we've been
> here). It could have been there for years, or ... maybe it started when
> the electrician was working there?
>
> The electrician said that it was the wrong side of the fuse box for him
> to do anything about it, but "we might want to get the Supplier" to look
> at it.
>
> I'm wary of doing that, because they are absolutely bound to find
> something wrong (now, aren't they?!) and we'll end up with a bill at
> least as big as the CH (£2800) to have the place "properly" rewired.
> (Maybe the electrician was hoping he'd get the job!)
>
> We rewired the house 15 years ago: I did most of the work, but was
> advised by a competent electrician from my place of work.
>
> Any thoughts, anyone?

I would ignore it unless it's warm or hot.

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

cj

unread,
Jun 27, 2008, 4:40:18 PM6/27/08
to
Hi
It's probably the sealant from the mains incoming cable .
The cable usually came into a spreader box of cast iron or similar where it
was terminated to the supply tails of the main fuse ,the whole lot was then
filled with a black "goo" similar to Tar or pitch.
You may be seeing the original overspill or a slight leakage which occurs as
the load increases and the joint warms up under peak demand.
Not a cause for worry unless you see strands (caused by molten sealant)
hanging from the box or the tar is hot.
Try checking the temperature of the joint box if its warm or hot contact
your supplier as it's their responsibility.
Otherwise don't worry.

HTH
CJ


The Wanderer

unread,
Jun 27, 2008, 5:22:18 PM6/27/08
to
On 27 Jun 2008 18:37:42 GMT, Andrew Gabriel wrote:

> In article <lalaw44-548B74...@plusnet.vsrv-ams.supernews.net>,
> Jonelle <lal...@hotmail.com> writes:
>> Hi all
>>
>> Background:
>> We recently had new CH installed. It required an electrician to come and
>> do the controls wiring. He looked in the cupboard housing our Consumer
>> Unit and mains connection, said the earthing was wrong, and fitted a new
>> earthing system (connecting CU, gas, etc all to the mains water in-pipe
>> under the sink). (He has charged £79 labour and £13 parts for doing
>> this; £109 inc VAT) (The CU and gas were previously earthed to a proper
>> earthing stake, hammered 2' into the ground under the cupboard, by me,
>> 15 years ago: he said he wasn't "getting a reading" from this.)
>>
>> Question:
>> Having done this, the guy pointed out to my wife (I was at work the
>> whole time he was here, else I'd have quizzed him a bit) that a black
>> substance was oozing out of the mains cable, at the point where it joins
>> the electricity supplier's fuse box (can't provide a picture sorry).
>>
>> This stuff, which looks like tar, is solid, and cold; however it has the
>> appearance of "flowing", and indeed it's already flowed over the
>> earthing strap that the electrician fitted, three weeks ago.

Hmm, I'd suspect the sparkie disturbed the cable termination when he fitted
the earthing clamp.

>> It's either
>> coming out of the cable pipe (it's the one about 1" wide, up through the
>> ground) or from the box it connects to (which precedes the actual mains
>> fuse box, before that connects to the CU).
>
> It's pitch,

More correctly, bitumen, aka A57 Compound.

>
>> I had never noticed this stuff before (ever, in the 22 years we've been
>> here). It could have been there for years, or ... maybe it started when
>> the electrician was working there?
>>
>> The electrician said that it was the wrong side of the fuse box for him
>> to do anything about it, but "we might want to get the Supplier" to look
>> at it.

No problems with that, but I'd get back to the sparkie anyway and make sure
he knows it's only been apparent since he did his work. The cable
termination may well have wooden bungs in the bottom, one of these will
have had a hole made in it when the cable was first installed and the
sparkie will probably have disturbed the cable when he fitted the clamp.
It's not unknown for the bungs to split in half.



>> I'm wary of doing that, because they are absolutely bound to find
>> something wrong

Unlikely. You tell the local distribution company that you have bitumen
leaking from the main fuse, it's their equipment. The guy(s) they send to
coreect it won't be 'wiring' electricians but a cable jointer or possibly
overhead linesman.

>
> I would ignore it unless it's warm or hot.

Don't ignore it, not if it's already oozed down to cover the earth clamp in
a matter of three weeks. You might just have a loose connection in the main
fuse that heats up slightly when you happen to have plenty of load switched
on, just enough to get the bitumen running out.

What they'll probably do is take off the old termination and fit a new one.
Shouldn't cost you anything. But, if they try to say that fitting the earth
clamp was the cause, then you tell them to charge electrician.

--
the dot wanderer at tesco dot net

Colin Wilson

unread,
Jun 27, 2008, 5:29:25 PM6/27/08
to

IIRC all iron-clad cutouts are supposed to be replaced by about 2012,
so call it through now and get it booked in.

newshound

unread,
Jun 27, 2008, 5:34:36 PM6/27/08
to

> Having done this, the guy pointed out to my wife (I was at work the
> whole time he was here, else I'd have quizzed him a bit) that a black
> substance was oozing out of the mains cable, at the point where it joins
> the electricity supplier's fuse box (can't provide a picture sorry).
>

I had a (non-technical) neighbour once in Bristol who asked me about
something similar; I told him his electricity must be coming from Pembroke
power station (which is oil fired). Should explain I'm in the nuclear
business.....


cynic

unread,
Jun 27, 2008, 6:13:26 PM6/27/08
to
On 27 Jun, 19:29, Jonelle <lala...@hotmail.com> wrote:
> Hi all
>
> Background:
> We recently had new CH installed. It required an electrician to come and
> do the controls wiring. He looked in the cupboard housing our Consumer
> Unit and mains connection, said the earthing was wrong, and fitted a new
> earthing system (connecting CU, gas, etc all to the mains water in-pipe
> under the sink).  (He has charged £79 labour and £13 parts for doing
> this; £109 inc VAT)  (The CU and gas were previously earthed to a proper
> earthing stake, hammered 2' into the ground under the cupboard, by me,
> 15 years ago: he said he wasn't "getting a reading" from this.)
>

A "proper" earthing stake would have a comparatively high resistance
path through the ground for a current to flow if you had a fault
situation in your house. Typical values of ground loop resistance lie
within 20 to 200 ohms so for a dead short between a line and earth you
would see currents of 11.5 to 1.1 amps Unless you have an RCD (earth
leakage circuit breaker) this will not cause disconnection of the
supply as a 6amp or higher circuit breaker would simply allow the
current to flow for an extended period, during which exposed metalwork
may be at a high(ish) voltage to earth and you or your family be at
risk of electrocution. Your electrician has bonded the main exposed
metalwork systems together which will minimse the voltage difference
between them in the event of a fault.
If he has connected this metalwork to the supply earth also then a low
resistance fault path should now be present (less than 1 ohm, probably
much less). This should provide a path for sufficient fault current to
cause operation of a fuse or circuit breaker, disconnect the supply
and achieve safety.
He should also have given you a certificate with test results thereon
of the situation after he had carried out the works.
This does of course assume that the supply earth is present and
securely connected. Earthing is a complex matter but I have tried to
simplify it above.


> Question:
> Having done this, the guy pointed out to my wife (I was at work the
> whole time he was here, else I'd have quizzed him a bit) that a black
> substance was oozing out of the mains cable, at the point where it joins
> the electricity supplier's fuse box (can't provide a picture sorry).

This is not uncommon but it may be that it is a relatively recent
development. If so you may have a problem which requires attention
quite rapidly


>
> This stuff, which looks like tar, is solid, and cold; however it has the
> appearance of "flowing", and indeed it's already flowed over the
> earthing strap that the electrician fitted, three weeks ago. It's either
> coming out of the cable pipe (it's the one about 1" wide, up through the
> ground) or from the box it connects to (which precedes the actual mains
> fuse box, before that connects to the CU).
>
> I had never noticed this stuff before (ever, in the 22 years we've been
> here). It could have been there for years, or ... maybe it started when
> the electrician was working there?
>
> The electrician said that it was the wrong side of the fuse box for him
> to do anything about it, but "we might want to get the Supplier" to look
> at it.
>
> I'm wary of doing that, because they are absolutely bound to find
> something wrong (now, aren't they?!) and we'll end up with a bill at
> least as big as the CH (£2800) to have the  place "properly" rewired.  
> (Maybe the electrician was hoping he'd get the job!)
>
> We rewired the house 15 years ago: I did most of the work, but was
> advised by a competent electrician from my place of work.

No comment

>
> Any thoughts, anyone?

If the pitch is flowing this shows that it is being heated up, thus
softening it. Was there any notable added load to your installation
recently? The central heating would be a negligible addition unles you
were going for a number of electrical heaters, however "controls
Wiring" suggests you have gone for gas or oil?
You sound unlikely to have means of measuring current in your supply
conductors but the electricity meter would be a good way of estimating
what current is flowing. Take a reading, wait 60 minutes and take a
second reading. Deduct reading 1 from reading 2, divide the difference
by 230 and the result is the average current in amps over the period.
This will have errors if some of the loads are under thermostat
control etc but it will give a broad picture

I would be concerned that a high resistance joint may be developing in
the service head. At best you may lose supply, at worst your house
could burn down. Call in the supplier to check it as you have been
advised

>
> Cheers
> John

Jonelle

unread,
Jun 28, 2008, 5:10:27 AM6/28/08
to
Dear all

*Many* thanks for the prompt and reassuring advice here. Slightly
worried (naturally) by Cynic's contribution -- partly because I don't
understand it, and we all fear that which we do not understand!

I will now keep a close watch on it, and if things get worse, will take
the advice to call in the supplier.

John

Andy Wade

unread,
Jun 28, 2008, 5:36:44 AM6/28/08
to
The Wanderer wrote:

> More correctly, bitumen, aka A57 Compound.

Which I see, just out of interest, is still available:
http://www.etscc.co.uk/jkcm/plugins/ProductsInCategory.aspx?cat=3843

--
Andy

Andy Wade

unread,
Jun 28, 2008, 6:20:19 AM6/28/08
to
Jonelle wrote:

> *Many* thanks for the prompt and reassuring advice here. Slightly
> worried (naturally) by Cynic's contribution -- partly because I don't
> understand it, and we all fear that which we do not understand!

Well you originally said

> (The CU and gas were previously earthed to a proper earthing stake,
> hammered 2' into the ground under the cupboard, by me, 15 years ago

There's nothing at all proper about that. An earth electrode for 'TT
system' earthing needs to be at least 4 ft. long in most cases and
should be outside, not under the house floor. This type of earthing is
only effective when used in conjunction with RCD protection (or the
older type of ELCB 'trip switch').

It seems to me the electrician here has acted with good intent, but not
necessarily full competence. He's converted the earthing to the TN-S
system by making a connection to the metal sheath of the distribution
network operator's (DNO's) cable. However this wasn't really for him to
do, as only the DNO should make such a connection. As pointed out in
another recent thread there are potentially serious dangers in fitting
certain types of earth clamps to old service cables. That thread also
revealed that at least one DNO no longer offers TN-S earth connections
and insists on conversion to the PME system (protective multiple
earthing, aka TN-C-S). Again the point is that the provision of either
type of metallic earth facility (or none) is at the DNO's discretion,
not your electrician's.

> I will now keep a close watch on it, and if things get worse, will take
> the advice to call in the supplier.

Follow The Wanderer's authoritative advice and call the DNO anyway.

--
Andy

tony sayer

unread,
Jun 28, 2008, 6:54:56 AM6/28/08
to
In article <6cmf1dF...@mid.individual.net>, Andy Wade <spambucket@m
axwell.myzen.co.uk> scribeth thus

See copper earth tape is now POA.. Hate to ask how much;!..
--
Tony Sayer

Reply all
Reply to author
Forward
0 new messages