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Topic Title: CAT Scan pickup of comms cables
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Created On: 01 February 2013 09:41 AM
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 01 February 2013 09:41 AM
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irnbru

Posts: 32
Joined: 23 April 2002

Hi
Would a CAT scan be expected to pickup comms underground cables?
The cables I have in mind are BS5208 with 4-20mA 24V instrumentatioin signals at a depth of 0.5m to 1m or say telephone cables.
or
Are CAT scans only for 600/1000V LV or HV cables?

Thanks and Regards

Peter
 01 February 2013 01:15 PM
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DHourston

Posts: 8
Joined: 23 May 2007

Hi irnbdu,

There doesn't need to be voltage present to pick up cables, any metallic object can be located, the mass of the cable you are trying to find is what will make it more difficult.

I would apply a signal to the cable (with the optional signal generator), should make your task much easier.

Regards

-------------------------
Regards

Dave H
 01 February 2013 02:25 PM
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DOUGIE1000

Posts: 4164
Joined: 13 August 2005

install 3 phase on it and use it to run the local air con unit until CAT picks it up.

:-)

Try one of THESE

Just messing about

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 04 February 2013 09:54 AM
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irnbru

Posts: 32
Joined: 23 April 2002

It was too late to use the spade Dougie as the ground workers beat me to it. Their spade was a bit bigger i.e. JCB

Should the CAT scan not have picked up the 2x 12 core BS5208 cables even though they were only 0.5m down albeit in platic downpipe containment??

FYI: The site is operational and has poor history regarding cable runs so it is unfeasible to inject cables.
 04 February 2013 10:08 AM
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DHourston

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I presume someone wants to point the finger of blame?

Now that the helpful civils team have exposed the cable can you not test the reliability of the CAT on the actual instsallation?

-------------------------
Regards

Dave H
 04 February 2013 12:38 PM
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dlane

Posts: 690
Joined: 28 September 2007

Originally posted by: irnbru

Should the CAT scan not have picked up the 2x 12 core BS5208 cables even though they were only 0.5m down albeit in platic downpipe containment??

FYI: The site is operational and has poor history regarding cable runs so it is unfeasible to inject cables.


The plastic containment should not affect the operation of the CAT scanner. I am not aware of the construction of a BS5208 cable, you would stand more chance of it being picked up by a CAT scanner if it is an SWA cable, if not it will take a very skilled and experienced operator of the scanner to detect it. As DHourston points out the best way to find it is to inject the scanner signal into it. If the cable has an outer shield then you can inject onto that via a core clamp and not connect directly onto it.

When we dig in areas where we suspect there may be some cabling then we would have a banksman watching the dig and the JCB would take shallow cuts out of the ground. I have come across some very good JCB operators that can feel when the bucket hits something and will stop to allow hand digging to find what is down there.

Kind regards

Donald Lane
 04 February 2013 01:09 PM
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oneye

Posts: 164
Joined: 25 February 2008

A few years ago I had to teach myself how to use a CATSCAN unit.
IMO
- It does not pickup 'dead' cables
- It does not pickup cable with AC voltage but open circuit end.
- It will pickup with very small current passing (in my case small 100 VA transformer with no load).

And as stated earlier it will pickup if signal inject used; which is more useful if you have several cables merging / diverging.
 05 February 2013 05:50 PM
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DOUGIE1000

Posts: 4164
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if this is a burst cable i wouldnt be worried in how you are going to find it i would be worried about how you are going to repair the join and keep it trouble free for years to come

-------------------------
Dougie
Power Plus Electrical.co.uk

My mission is to live as long as possible......so far so good!
 05 February 2013 08:54 PM
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slittle

Posts: 3510
Joined: 22 November 2007

Originally posted by: dlane

Originally posted by: irnbru



Should the CAT scan not have picked up the 2x 12 core BS5208 cables even though they were only 0.5m down albeit in platic downpipe containment??



FYI: The site is operational and has poor history regarding cable runs so it is unfeasible to inject cables.




The plastic containment should not affect the operation of the CAT scanner. I am not aware of the construction of a BS5208 cable, you would stand more chance of it being picked up by a CAT scanner if it is an SWA cable, if not it will take a very skilled and experienced operator of the scanner to detect it. As DHourston points out the best way to find it is to inject the scanner signal into it. If the cable has an outer shield then you can inject onto that via a core clamp and not connect directly onto it.



When we dig in areas where we suspect there may be some cabling then we would have a banksman watching the dig and the JCB would take shallow cuts out of the ground. I have come across some very good JCB operators that can feel when the bucket hits something and will stop to allow hand digging to find what is down there.



Kind regards



Donald Lane



Agreed Donald,

Although we've had one "near miss" on a farm where an HV cable which was successfully cat'd and marked was scuffed by the digger because it was only 600mm down when expected a lot deeper generally with an alert banksman and a good machine operator most cable damage can be avoided.

We've successfully found cat5 in a pipe using a cat and genny, also found it in the middle of a field using two bent copper rods and the old fashioned divining methods but I wouldn't recommend being seen on a "proper" site doing it

Stu
 05 February 2013 09:25 PM
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Zs

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Hopefully, BOD will see your post irnbru.

He's a dab hand at this stuff and particularly good with a divining rod. I think divining may be a practiced skill but having seen it in action it is pretty impressive. Cheap and quick but I really don't know how it works.


Zs
 05 February 2013 09:48 PM
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slittle

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Me neither Zs, but it works well.

I can do it pretty much spot on every time but I'm damned if I can explain how or why it works.

Rumour has it my great,great grandfather used to make a living at it so perhaps it's a skill that certain people have and others dont.


Stu
 05 February 2013 10:58 PM
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alancapon

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Originally posted by: slittle
. . . we've had one "near miss" on a farm where an HV cable which was successfully cat'd and marked was scuffed by the digger because it was only 600mm down when expected a lot deeper . . .

That can often be a problem. We all know how deep cables of various voltages should be. Sometimes, we know how deep they were when last seen. What does confuse things is when the ground level is changed, and they end up (usually) shallower than expected.

. . . also found it in the middle of a field using two bent copper rods and the old fashioned divining methods but I wouldn't recommend being seen on a "proper" site doing it . . .

Again, I have tried that too. For reasons I am unable to explain, it does seem to work, and can be as accurate as a CAT & Genny! I have also located LV joints using similar methods.


Regards,

Alan.
 06 February 2013 03:30 PM
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ArthurHall

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When I was a DNO engineer we had an old divining set very well made and in a lovely varnished wood case complete with instructions and samples of lead, copper, pipeclay etc. Aparently if you have a piece of the material you are looking for in your hand it increases the sensitivity.
 06 February 2013 03:30 PM
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ArthurHall

Posts: 735
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When I was a DNO engineer we had an old divining set very well made and in a lovely varnished wood case complete with instructions and samples of lead, copper, pipeclay etc. Aparently if you have a piece of the material you are looking for in your hand it increases the sensitivity.
 06 February 2013 11:09 PM
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kirchoffs

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I've used a pair homemade rods for years with about 90% success rate, The secret is to hold the rods very loosely so they can turn easily.

Regards Dominic
 06 February 2013 11:28 PM
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Zs

Posts: 2904
Joined: 20 July 2006

Originally posted by: ArthurHall

Aparently if you have a piece of the material you are looking for in your hand it increases the sensitivity.


I can see that. Everything resonates differently so holding a piece of your target could well work better than not.

I once tried to make myself some 'elixir'; I had read that if you put a chunk of quartz in a glass of pure water, in the moonlight and with seven small chunks arranged around the glass that the energies of the quartz would make a healing tonic. Cheaper than botox thought I, So I did it and I used a high ball glass with straight sides and a thick bottom. My quartz chunk was a torpedo in the form of a twin complete with an air bubble inside it, with a drop of water in the bubble. Quite rare. My seven chunks were smaller torpedos. All in a moonbeam on the bathroom window ledge under a full moon. at 3am I was woken to a massive cracking sound which I couldn't trace. Next morning I picked up the glass and the bottom fell away, perfectly severed in a ring but with seven tiny V shapes in perfect formation. Resonance. I do buy into it but how can it work in an open field with the diggers rattling around etc?

That magnetism word comes to mind.

Zs
 07 February 2013 01:01 PM
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marclambert

Posts: 310
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How lovely Zs,
You don't by any chance know of any spells for dealing with unruly students do you?
I was thinking large lumps of rock might be involved and not necessarily quartz.
 08 February 2013 05:28 PM
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perspicacious

Posts: 7232
Joined: 18 April 2006

"Hopefully, BOD will see your post irnbru.
He's a dab hand at this stuff and particularly good with a divining rod. I think divining may be a practiced skill but having seen it in action it is pretty impressive. Cheap and quick but I really don't know how it works."


Well on Monday, I've got to find the route of about 70 m of soakaway and the most reliable way is to cobra rod it with an integral wired core, connect the Genny to it and CAT it but as the only known point is the exit in a very wet ditch, I've decided that "witchcraft" is the preferred first option Besides, I expect the soakaway is silted up making rodding impossible.

I'll pass on holding a sample of searched for material

Regards

BOD
 08 February 2013 06:02 PM
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rocknroll

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Joined: 03 October 2005

I've decided that "witchcraft" is the preferred first option


LOL I quite believe that, I met a few witches in that part of the world in my troubled youth.

regards

-------------------------
"Take nothing but a picture,
leave nothing but footprints!"
-------------------------
"Oh! The drama of it all."
-------------------------
"You can throw all the philosophy you like at the problem, but at the end of the day it's just basic electrical theory!"
-------------------------
 08 February 2013 08:29 PM
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perspicacious

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Joined: 18 April 2006

"I met a few witches in that part of the world in my troubled youth"

Oddly enough, I stopped at Leominster market today and bought a little present for our end of circuit impedance

Regards

BAD

http://en.wikipedia.org/wiki/Common_scold
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