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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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#1
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Finding armoured cable underground
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 |
#2
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Finding armoured cable underground
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 http://www.cal-services.net/how-to £46 for a weekend from Jewson Hire online http://www.jewson.co.uk/tool-hire/su...avoiding-tool/ £50 a week from Speedy https://www.speedyservices.com/24_60...avoidance-tool Owain |
#3
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Finding armoured cable underground
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#4
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Finding armoured cable underground
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. 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. Have you tested each core for continuity independently of the supply? Mike |
#5
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Finding armoured cable underground
Would one of those cheapo combined stud/cable finders work?
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#6
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Finding armoured cable underground
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 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. |
#7
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Finding armoured cable underground
In message ,
Muddymike 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 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 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 |
#9
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Finding armoured cable underground
In message , Andy Burns
writes 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 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. 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 |
#10
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Finding armoured cable underground
In article ,
Bill 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 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 London SW To e-mail, change noise into sound. |
#11
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Finding armoured cable underground
"Mike Tomlinson" wrote in message
... En el artículo , 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 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 |
#12
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Finding armoured cable underground
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) Owain |
#13
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Finding armoured cable underground
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. |
#14
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Finding armoured cable underground
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 |
#15
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Finding armoured cable underground
On 23/05/2016 16:25, Bill wrote:
In message , Andy Burns writes 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 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. 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. Stick 240V on the armour. Make sure the other end is genuinely isolated. Then try the cable finder. Of course it is possible that all the earth above will shield the cable. |
#16
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Finding armoured cable underground
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... Blind user, so no pictures please! "Mike Tomlinson" wrote in message ... En el artículo , 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 |
#17
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Finding armoured cable underground
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 , Brian Gaff escribió: Not sure that is going to work. Most of this sort of cable tends to be screened by the armour which is earthed. -- (\_/) (='.'=) Windows 10: less of an OS, more of a drive-by mugging. (")_(") -- "Esme" on el Reg |
#18
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Finding armoured cable underground
In message , Mike Tomlinson
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 , Brian Gaff 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 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 |
#19
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Finding armoured cable underground
On 5/23/2016 12:58 PM, wrote:
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 http://www.cal-services.net/how-to £46 for a weekend from Jewson Hire online http://www.jewson.co.uk/tool-hire/su...avoiding-tool/ £50 a week from Speedy https://www.speedyservices.com/24_60...avoidance-tool Owain +1. Forget using stud finders, radios, etc. |
#20
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Finding armoured cable underground
In message , Tim Lamb
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... 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 |
#21
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Finding armoured cable underground
Bill wrote:
In message , Tim Lamb 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... 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. I think I'd try measuring the cable capacity and resistance with a 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! |
#22
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Finding armoured cable underground
On Mon, 23 May 2016 12:06:39 +0100, 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. 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. Starting with the assumption that you can check the sheathing for 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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