We do not know what other cables are contributing to this (very small) drop.
Finding length of cable
- Thread starter oceansoul
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I would agree neutral - earth voltage likely more accurate. This is why I gave the range moving 0.1 volt either way and 0.1 amp either way.
I do know the problems with pumping stations I worked on North West Waters for a time. We got a 8 figure map reference. Found one under a band stand, one in middle of roundabout over a motorway, and one built to blend in with the garden wall. Even built into the Blackpool front.
My job was to agree what was needed to upgrade them to modern regulations there were a couple I just said rip it out and start again must have been installed to first edition.
Often there was no DNO meter or head as normally found and no seals on fuses clearly the DNO trusted the water company. Although owned by water board maintained by county council so one could very well have the street lights and water pump from same supply.
So there may not be a distribution board in the normal way.
I do know the problems with pumping stations I worked on North West Waters for a time. We got a 8 figure map reference. Found one under a band stand, one in middle of roundabout over a motorway, and one built to blend in with the garden wall. Even built into the Blackpool front.
My job was to agree what was needed to upgrade them to modern regulations there were a couple I just said rip it out and start again must have been installed to first edition.
Often there was no DNO meter or head as normally found and no seals on fuses clearly the DNO trusted the water company. Although owned by water board maintained by county council so one could very well have the street lights and water pump from same supply.
So there may not be a distribution board in the normal way.
If you can find out the dc resistance of a known length (i.e. 1 meter) for a single core and then divide the total resistance of 1 core by the resistance of 1 meter, you should be able to get an idea of the length of the cable.
See this table for known resistance of swa copper conductor resistances: http://www.batt.co.uk/upload/files/xlpeswalszhbs6724_1227548172.pdf
i.e. 4mm SWA copper conductors have a resistance of 4.61 milliohms per meter, so if you measure 330 milliohms of one the conductors in the swa from end to end; divide the result of 330 by 4.61 and you will get a result of 71.58 meters.
Traps to watch out for:
1) Most multi meters can only measure down to 0.1 (100 milliohms) of an ohm and have a tolerance of 1-2%.
2) Don't forget to include the resistance of the test leads and account for the test leads resistance in your readings.
3) Watch out for things like junction boxes, other cables connected in series, unforeseen loops that act as a bypass,etc... what will give you incorrect readings.
Edit: Just read your post again
, and realize you only have access to one end of the cable. You may be better off renting a machine like they use on time-team that is normally used to survey the ground. I believe it is called a ground-penetrating radar machine.
See this table for known resistance of swa copper conductor resistances: http://www.batt.co.uk/upload/files/xlpeswalszhbs6724_1227548172.pdf
i.e. 4mm SWA copper conductors have a resistance of 4.61 milliohms per meter, so if you measure 330 milliohms of one the conductors in the swa from end to end; divide the result of 330 by 4.61 and you will get a result of 71.58 meters.
Traps to watch out for:
1) Most multi meters can only measure down to 0.1 (100 milliohms) of an ohm and have a tolerance of 1-2%.
2) Don't forget to include the resistance of the test leads and account for the test leads resistance in your readings.
3) Watch out for things like junction boxes, other cables connected in series, unforeseen loops that act as a bypass,etc... what will give you incorrect readings.
Edit: Just read your post again
, and realize you only have access to one end of the cable. You may be better off renting a machine like they use on time-team that is normally used to survey the ground. I believe it is called a ground-penetrating radar machine.Sponsored Links
I think the OP understands that, but the problem is that he cannot measure the resistance 'from end to end' - since he only has one end, and the whole purpose of what he wants to do is to try to work out how far away (wherever) the other (so far undiscovered) end is!
Kind Regards, John
Often get this in large superstores, if possible go in at a convenient time so you can shut off submains at the main intake, till you find what Dist board its from then go from there.
other options a cable tracer connected to the panel that sends a signal back down the mains that you locate with a receiver
other options a cable tracer connected to the panel that sends a signal back down the mains that you locate with a receiver
Do I take it that tracers are available that can do that (safely!) on a live cable?
Kind Regards, John
Yes. I have one and it's invaluable. It takes a bit of getting the hang of how to use it, but once you've mastered it you can get the right circuit every time.
I have this one
http://www.tester.co.uk/socket-and-...inder-kit-uk?gclid=COCojeCpzsICFY3JtAodtA4ATA
I have this one
http://www.tester.co.uk/socket-and-...inder-kit-uk?gclid=COCojeCpzsICFY3JtAodtA4ATA
Interesting. As you say, it sounds pretty useful. Do you get any problems from 'cross-coupling' of adjacent cables (any idea what sort of frequency it uses?)?
Kind Regards, John
No it's quite clever how the receiver works. As you scan the row of fuses the receiver automatically desensitises it's self until the point where you only get a strong signal on the fuse supplying the circuit the transmitter is connected to.
It's quite hard to explain without actually seeing it in action!
There's a video here from the manufacturer which might help a bit.
http://www.socketandsee.co.uk/vidpop.asp?productID=2
It's quite hard to explain without actually seeing it in action!
There's a video here from the manufacturer which might help a bit.
http://www.socketandsee.co.uk/vidpop.asp?productID=2
Interesting - it sounds quite clever!
Thanks. I'll have a look when I have a moment.
Kind Regards, John
Theoretically I see no reason why it shouldn't be possible, the operating frequency would be nowhere near mains frequency and i'm sure the DB supplying the circuit would be a plenty big enough discontinity to provide a detectable refelction.
Practically you would need either an instrument designed for the job or a carefully designed protection network between instrument and mains wiring
The best place to look is in the documentation for the site's electrical installation.
If you are working on a cabinet you should be informed as to where the power supply comes from and who to contact should you need to have power removed from the cabinet. The fact that there is an isolator in the cabinet does not make any difference. There will be live connections on one side of the isolator.
In an ideal world there would be clear policies in place from initial installation to present day on who was responsible for holding the documentation for the installation (or in a really big installation parts of it) and how changes are to be recorded in that documentation and those policies would have been merticulously followed from the initial installation to the present day.
In the real world unfortunately that doesn't always happen.
In the real world unfortunately that doesn't always happen.
http://www.fluke.com/fluke/m2en/Electrical-Testers/Electrical-Testers/Fluke-2042.htm?PID=56052
What I liked about it was the 3 codes, so you could get an assistant to change the codes at the other end or simply turn it off and it helped you confirm a proper signal at the receiver rather than a roque one.
Quite often the receiver gives a misleading tone, but 90 % of the time it has helped.
Takes a bit of practise as RF said
At 400 pound its not the cheapest option, unfortunately it was recently stolen from my van in broad daylight on a tesco loading bay
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