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Finding armoured cable underground
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Bill
May 23, 2016, 7:09:28 AM5/23/16
to
This week's problem on my son's house is that all the power has failed
to a set of outbuildings.
The cabling is confusing and has obviously been modified by the previous
owner of the house who was, perhaps, a little eccentric in his approach
to colour coding.
Armoured cable leaves the house and appears in 2 boxes feeding some
lights, a garage and the outbuilding area. Power seems to be leaving
these boxes via armoured cables, but no power is arriving at the
outbuildings.
We suspect there may be an underground junction box that fed a pond pump
in the past, but digging has not located this. We have consulted an
electrician who said the cost effective way would be to replace the
cable. His estimate was beyond our budget.
What is the best way for us to locate the cables underground? Is a cheap
metal detector likely to be the best bet or work at all? I can't find
mine under all the junk in the garage, so is there a best, cheap type to
look for or are they all much the same?
We have spent some time in the undergrowth poking around. I have 15
bites on my legs as a result.
--
Bill
to a set of outbuildings.
The cabling is confusing and has obviously been modified by the previous
owner of the house who was, perhaps, a little eccentric in his approach
to colour coding.
Armoured cable leaves the house and appears in 2 boxes feeding some
lights, a garage and the outbuilding area. Power seems to be leaving
these boxes via armoured cables, but no power is arriving at the
outbuildings.
We suspect there may be an underground junction box that fed a pond pump
in the past, but digging has not located this. We have consulted an
electrician who said the cost effective way would be to replace the
cable. His estimate was beyond our budget.
What is the best way for us to locate the cables underground? Is a cheap
metal detector likely to be the best bet or work at all? I can't find
mine under all the junk in the garage, so is there a best, cheap type to
look for or are they all much the same?
We have spent some time in the undergrowth poking around. I have 15
bites on my legs as a result.
--
Bill
spuorg...@gowanhill.com
May 23, 2016, 7:58:21 AM5/23/16
to
On Monday, 23 May 2016 12:09:28 UTC+1, Bill wrote:
> We suspect there may be an underground junction box that fed a pond pump
> in the past, but digging has not located this. We have consulted an
> electrician who said the cost effective way would be to replace the
> cable. His estimate was beyond our budget.
> What is the best way for us to locate the cables underground?
Hire a CAT scanner and genny for the weekend, or find someone who's got one
> We suspect there may be an underground junction box that fed a pond pump
> in the past, but digging has not located this. We have consulted an
> electrician who said the cost effective way would be to replace the
> cable. His estimate was beyond our budget.
> What is the best way for us to locate the cables underground?
http://www.cal-services.net/how-to
£46 for a weekend from Jewson Hire online
http://www.jewson.co.uk/tool-hire/surveying-equipment/surveying/products/7231/cable-avoiding-tool/
£50 a week from Speedy
https://www.speedyservices.com/24_6010-h-c-scope-cxl-cable-avoidance-tool
Owain
Mike Tomlinson
May 23, 2016, 8:41:41 AM5/23/16
to
En el artículo <bd2c2894-75b7-485a...@googlegroups.com>,
spuorg...@gowanhill.com escribió:
>Hire a CAT scanner and genny for the weekend, or find someone who's got one
I was wondering if the following would work (I haven't tried it). It
would be cheaper than hiring equipment.
Disconnect the cable at the remote end and insulate.
Disconnect the house end (in the 2 boxes in the garage?), put a diode in
the live feed so the result is 25Hz rectified mains fed into the cable
to the outbuildings.
Use an AM radio at the point where the cable leaves the 2 boxes and tune
it until it finds the 25Hz hum, then follow the signal until it is lost,
that's where to dig.
If the signal appears all the way to the remote end, then the live wire
is ok. Repeat, but with the diode in the neutral wire instead.
This is assuming there isn't a short to neutral or earth (the OP hasn't
said if fuses/breakers are tripping.)
--
(\_/)
(='.'=) Windows 10: less of an OS, more of a drive-by mugging.
(")_(") -- "Esme" on el Reg
spuorg...@gowanhill.com escribió:
>Hire a CAT scanner and genny for the weekend, or find someone who's got one
would be cheaper than hiring equipment.
Disconnect the cable at the remote end and insulate.
Disconnect the house end (in the 2 boxes in the garage?), put a diode in
the live feed so the result is 25Hz rectified mains fed into the cable
to the outbuildings.
Use an AM radio at the point where the cable leaves the 2 boxes and tune
it until it finds the 25Hz hum, then follow the signal until it is lost,
that's where to dig.
If the signal appears all the way to the remote end, then the live wire
is ok. Repeat, but with the diode in the neutral wire instead.
This is assuming there isn't a short to neutral or earth (the OP hasn't
said if fuses/breakers are tripping.)
--
(\_/)
(='.'=) Windows 10: less of an OS, more of a drive-by mugging.
(")_(") -- "Esme" on el Reg
Muddymike
May 23, 2016, 9:06:58 AM5/23/16
to
Mike
GB
May 23, 2016, 10:09:35 AM5/23/16
to
Would one of those cheapo combined stud/cable finders work?
Andy Burns
May 23, 2016, 10:36:11 AM5/23/16
to
GB wrote:
> Would one of those cheapo combined stud/cable finders work?
When set to detect live cables, my Bosch GMS120 will detect a piece of
> Would one of those cheapo combined stud/cable finders work?
plasterboard that's in contact with a mains cable at about 18" (i.e.
useless false negative) but it won't detect SWA even when touching it.
In metalwork mode it detects the SWA, but not at any useful distance.
Bill
May 23, 2016, 11:27:06 AM5/23/16
to
In message <bd2c2894-75b7-485a...@googlegroups.com>,
spuorg...@gowanhill.com writes
I've been looking at that sort of thing, but wasn't sure how it would
work with armoured cable. I assume (probably wrongly) that the method of
looking for pipes rather than powered cable would have to be used.
He and I also have a track record of getting to "It has to be done this
weekend" and thus inducing the worst storms since records began, so I'd
like to be confident before hiring.
--
Bill
spuorg...@gowanhill.com writes
work with armoured cable. I assume (probably wrongly) that the method of
looking for pipes rather than powered cable would have to be used.
He and I also have a track record of getting to "It has to be done this
weekend" and thus inducing the worst storms since records began, so I'd
like to be confident before hiring.
--
Bill
Bill
May 23, 2016, 11:27:07 AM5/23/16
to
In message <tv-dnX81X_7ynd7K...@brightview.co.uk>,
Muddymike <ne...@mattishall.org.uk> writes
red, white and blue from the armoured cable, plus some green/yellow and
brown. I think we gave up when we were at the stage where we agreed that
live went in on white and emerged 100 yards away on red.
I do need to do a lot more physical testing.
--
Bill
Muddymike <ne...@mattishall.org.uk> writes
>On 23/05/2016 12:06, Bill wrote:
>> This week's problem on my son's house is that all the power has failed
>> to a set of outbuildings.
>> The cabling is confusing and has obviously been modified by the previous
>> owner of the house who was, perhaps, a little eccentric in his approach
>> to colour coding.
<Snip>
>> This week's problem on my son's house is that all the power has failed
>> to a set of outbuildings.
>> The cabling is confusing and has obviously been modified by the previous
>> owner of the house who was, perhaps, a little eccentric in his approach
>> to colour coding.
>>
> Have you tested each core for continuity independently of the supply?
>
The problem is our confusion over the colours. In the 2 boxes we have
> Have you tested each core for continuity independently of the supply?
>
red, white and blue from the armoured cable, plus some green/yellow and
brown. I think we gave up when we were at the stage where we agreed that
live went in on white and emerged 100 yards away on red.
I do need to do a lot more physical testing.
--
Bill
Bill
May 23, 2016, 11:27:07 AM5/23/16
to
In message <dqgiqn...@mid.individual.net>, Andy Burns
<feb2017...@adslpipe.co.uk> writes
We did try his stud finder, but nothing.
He also has a warbly-tone cable tracer, but it appeared to have lost all
its gain at one end or the other. It said 120dB output in the
instructions, but we had to hold it about 6 inches away to hear it at
all.
--
Bill
<feb2017...@adslpipe.co.uk> writes
He also has a warbly-tone cable tracer, but it appeared to have lost all
its gain at one end or the other. It said 120dB output in the
instructions, but we had to hold it about 6 inches away to hear it at
all.
--
Bill
Dave Plowman (News)
May 23, 2016, 11:59:11 AM5/23/16
to
In article <ByQENBCu...@itsound.demon.co.uk>,
colours were red blue and yellow. Most used red - line, blue - neutral,
yellow - earth. But of course you can't be certain of this. The correct
colour tape or sleeves should really have been used to identify it.
Before I bought this house, the leccy meter was moved from the cellar to
the top of the cellar stairs. 3 core armoured was used for this with those
3 phase colours. The leccy board used the colours as I've given.
--
*Where do forest rangers go to "get away from it all?"
Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.
Bill <Billa...@gmail.com> wrote:
> The problem is our confusion over the colours. In the 2 boxes we have
> red, white and blue from the armoured cable, plus some green/yellow and
> brown. I think we gave up when we were at the stage where we agreed that
> live went in on white and emerged 100 yards away on red.
Armoured cable - 3 core - is often 3 phase colours. The old 3 phase
> The problem is our confusion over the colours. In the 2 boxes we have
> red, white and blue from the armoured cable, plus some green/yellow and
> brown. I think we gave up when we were at the stage where we agreed that
> live went in on white and emerged 100 yards away on red.
colours were red blue and yellow. Most used red - line, blue - neutral,
yellow - earth. But of course you can't be certain of this. The correct
colour tape or sleeves should really have been used to identify it.
Before I bought this house, the leccy meter was moved from the cellar to
the top of the cellar stairs. 3 core armoured was used for this with those
3 phase colours. The leccy board used the colours as I've given.
--
*Where do forest rangers go to "get away from it all?"
Dave Plowman da...@davenoise.co.uk London SW
To e-mail, change noise into sound.
Dave W
May 23, 2016, 12:14:46 PM5/23/16
to
"Mike Tomlinson" <mi...@jasper.org.uk> wrote in message
news:4pFtOqB8...@jasper.org.uk...
I used a similar method to find a break in a 'hearing loop' round a lecture
room. I constructed an oscillator giving out 8KHz at 250V rms, and connected
it to one end of the isolated loop. I could hear the whistle from it in a
pair of high-impedance ex-WD headphones, one terminal connected to a metal
plate waved about 6" from the wall and the other held in my hand. The break
was where the whistle stopped. In fact the break was about a 6 metre gap
where decorators had ripped out what they must have thought was some ancient
unused bell wire.
In your case with armoured cable, the metal armour encloses all cores, so
you won't be able to detect a break, owing to the capacitance between the
cores and the armour, but at least you might find where it runs.
Another thing to try is to measure the capacitance between each cable and
the armour. Do this at both ends. The readings might indicate how far along
the length is the break.
--
Deve W
news:4pFtOqB8...@jasper.org.uk...
room. I constructed an oscillator giving out 8KHz at 250V rms, and connected
it to one end of the isolated loop. I could hear the whistle from it in a
pair of high-impedance ex-WD headphones, one terminal connected to a metal
plate waved about 6" from the wall and the other held in my hand. The break
was where the whistle stopped. In fact the break was about a 6 metre gap
where decorators had ripped out what they must have thought was some ancient
unused bell wire.
In your case with armoured cable, the metal armour encloses all cores, so
you won't be able to detect a break, owing to the capacitance between the
cores and the armour, but at least you might find where it runs.
Another thing to try is to measure the capacitance between each cable and
the armour. Do this at both ends. The readings might indicate how far along
the length is the break.
--
Deve W
spuorg...@gowanhill.com
May 23, 2016, 12:31:18 PM5/23/16
to
On Monday, 23 May 2016 16:27:06 UTC+1, Bill wrote:
> I've been looking at that sort of thing, but wasn't sure how it would
> work with armoured cable. I assume (probably wrongly) that the method of
> looking for pipes rather than powered cable would have to be used.
I think you can attach the genny part to the armour of the cable, which should be insulated from earth by the cable sheathing, and get a signal radiated that way (disconnect the armour from cpc at the circuit ends)
> I've been looking at that sort of thing, but wasn't sure how it would
> work with armoured cable. I assume (probably wrongly) that the method of
> looking for pipes rather than powered cable would have to be used.
Owain
GB
May 23, 2016, 2:59:57 PM5/23/16
to
On 23/05/2016 16:48, Jethro_uk wrote:
> Since it costs **** all, you could always try dowsing ?
>
> I have seen it done, and "work" for sewers. That's all I will say, since
> the "science" a lot of people peddle about it is clearly claptrap.
>
My own pet theory (again in a minority of one) is that the dowsing rod
amplifies any deviation from standing vertically in the person holding
it. Above a sewer pipe the ground has compacted since it was buried, so
there's a small dip, maybe to small to notice. As you walk over it your
body moves away from vertical. Just a thought.
> Since it costs **** all, you could always try dowsing ?
>
> I have seen it done, and "work" for sewers. That's all I will say, since
> the "science" a lot of people peddle about it is clearly claptrap.
>
My own pet theory (again in a minority of one) is that the dowsing rod
amplifies any deviation from standing vertically in the person holding
it. Above a sewer pipe the ground has compacted since it was buried, so
there's a small dip, maybe to small to notice. As you walk over it your
body moves away from vertical. Just a thought.
polygonum
May 23, 2016, 3:25:06 PM5/23/16
to
On 23/05/2016 12:06, Bill wrote:
> What is the best way for us to locate the cables underground?
Much easier to find it on a cable drum in an electrical thingies supplier.
--
Rod
Fredxxx
May 23, 2016, 3:35:40 PM5/23/16
to
Then try the cable finder. Of course it is possible that all the earth
above will shield the cable.
Brian Gaff
May 24, 2016, 3:44:02 AM5/24/16
to
Not sure that is going to work. Most of this sort of cable tends to be
screened by the armour which is earthed.
You really needs one of those ground penetrating radars the archaeologists
use.
Brian
--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
bri...@blueyonder.co.uk
Blind user, so no pictures please!
screened by the armour which is earthed.
You really needs one of those ground penetrating radars the archaeologists
use.
Brian
--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...
bri...@blueyonder.co.uk
Blind user, so no pictures please!
Mike Tomlinson
May 24, 2016, 5:31:39 AM5/24/16
to
Yes, I realised that later. One solution might be to feed the rectified
signal down the armour, with the remote end well isolated of course.
Dodgy though.
En el artículo <ni10h6$hqr$1...@dont-email.me>, Brian Gaff
<bri...@blueyonder.co.uk> escribió:
>Not sure that is going to work. Most of this sort of cable tends to be
>screened by the armour which is earthed.
Tim Lamb
May 24, 2016, 5:41:15 AM5/24/16
to
In message <33yO5vAn...@jasper.org.uk>, Mike Tomlinson
<mi...@jasper.org.uk> writes
box was used at the original load end by the securing gland.
If such a junction box were metal, it should give a good earth
connection..... I think you need some current flowing at 50HZ to
energize a cable finder.
>
--
Tim Lamb
<mi...@jasper.org.uk> writes
>
>Yes, I realised that later. One solution might be to feed the rectified
>signal down the armour, with the remote end well isolated of course.
>Dodgy though.
>
>En el artículo <ni10h6$hqr$1...@dont-email.me>, Brian Gaff
><bri...@blueyonder.co.uk> escribió:
>
>>Not sure that is going to work. Most of this sort of cable tends to be
>>screened by the armour which is earthed.
Presumably the armouring will have been connected to whatever junction
>Yes, I realised that later. One solution might be to feed the rectified
>signal down the armour, with the remote end well isolated of course.
>Dodgy though.
>
>En el artículo <ni10h6$hqr$1...@dont-email.me>, Brian Gaff
><bri...@blueyonder.co.uk> escribió:
>
>>Not sure that is going to work. Most of this sort of cable tends to be
>>screened by the armour which is earthed.
box was used at the original load end by the securing gland.
If such a junction box were metal, it should give a good earth
connection..... I think you need some current flowing at 50HZ to
energize a cable finder.
>
--
Tim Lamb
newshound
May 24, 2016, 7:40:32 AM5/24/16
to
Bill
May 24, 2016, 2:15:52 PM5/24/16
to
In message <Za8Pld+p...@marfordfarm.demon.co.uk>, Tim Lamb
<t...@marfordfarm.demon.co.uk> writes
At least one of the boxes will need replacing, and there are visible
problems with one of the securing glands. I believe all the armouring is
still earthed though.
The main armoured cables are definitely coded red, blue, white and one
box has 2 whites earthed to the box. The third white in the same box is
tested live.
There is a bit of a family dispute (long distance at the moment) about
what to do next. I think we need to disconnect and measure until we
understand exactly what each individual wire does and which direction
the power goes. Son thinks we just have to find a way to trace the cable
until we find the underground junction box that he thinks must be there.
Anyway, I have invested a small amount in a pre-loved metal detector on
ebay and will practise with it before he arrives back at the weekend. I
don't really expect it to work. It may have to detect cable under crazy
paving.
Running a new armoured cable on the surface tucked in at the base of
walls would be possible, but the amount of gardening work involved is
daunting and a couple of paths would have to be crossed.
--
Bill
<t...@marfordfarm.demon.co.uk> writes
>Presumably the armouring will have been connected to whatever junction
>box was used at the original load end by the securing gland.
>
>If such a junction box were metal, it should give a good earth
>connection..... I think you need some current flowing at 50HZ to
>energize a cable finder.
Just some notes on this and earlier comments...
>box was used at the original load end by the securing gland.
>
>If such a junction box were metal, it should give a good earth
>connection..... I think you need some current flowing at 50HZ to
>energize a cable finder.
At least one of the boxes will need replacing, and there are visible
problems with one of the securing glands. I believe all the armouring is
still earthed though.
The main armoured cables are definitely coded red, blue, white and one
box has 2 whites earthed to the box. The third white in the same box is
tested live.
There is a bit of a family dispute (long distance at the moment) about
what to do next. I think we need to disconnect and measure until we
understand exactly what each individual wire does and which direction
the power goes. Son thinks we just have to find a way to trace the cable
until we find the underground junction box that he thinks must be there.
Anyway, I have invested a small amount in a pre-loved metal detector on
ebay and will practise with it before he arrives back at the weekend. I
don't really expect it to work. It may have to detect cable under crazy
paving.
Running a new armoured cable on the surface tucked in at the base of
walls would be possible, but the amount of gardening work involved is
daunting and a couple of paths would have to be crossed.
--
Bill
Capitol
May 25, 2016, 6:40:20 AM5/25/16
to
DVM. Mine works down to about 10pF. By measuring each cable
individually, a break may show as reduced capacity, then measuring all
cables together relative to the shield will provide another guide.
Obviously the earth may be connected to the shield somewhere, so maybe
that's the point to go for a resistance measurement for the return path.
Looks like a very long pair of test leads are going to be required!
David
May 26, 2016, 8:28:25 AM5/26/16
to
electrical continuity - probably by fixing a wire at one end and leading
it back to the other end (after making sure everything else at the ends is
disconnected) - and there seems to be a break in the sheathing.
Possible partly non-electrical method.
Dig down at the start and end of the unknown run and extend the trench
about a foot along.
This should give you an idea of the depth of the cable and the direction
of the run.
If the two directions don't match, run a line along each direction and
suspect that the junction could be around where they meet. This would be a
good place to dig.
You might be able to firm up the precise cable run by using a long thin
metal probe - you can test your probing skills just past the trench
exposing your exposed bits of cable
If they are pointing in the same direction, I'm not sure how you could
test continuity part way along without cutting into the plastic covering
to get at the metal shielding.
Cheers
Dave R
--
Windows 8.1 on PCSpecialist box
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