How to trace next socket on the ring?

[scoobasteve]

Hi,

I have removed a wall in my house which contained a single socket on the downstairs ring main, cable has been temporarily joined with a terminal block.

How do I trace the 2 sockets either side in order that I can replace the jointed cable with one new length of cable between the sockets either side on the ring?

I have a mulimeter/continuity tester just need bit of advice on correct procedure to follow.

Cheers

 

[flameport]

Switch power off.
Unplug everything
At the join, connect the L and E wires from one side only together. Leave the other wires unconnected (the N and the L/N/E from the other side)

Go to the other socket outlets and measure the resistance between L and E.
The sockets either side of the join are the ones with the lowest and highest readings.

(This will only work if the ring is actually a ring - if you have spurs and other mess it won't work).

 

[ericmark]

I would just plug in the earth loop impedance tester and take reading these should progressively get higher as you approach centre of ring main and then get lower as one starts to return so two readings closest to reading taken at joint will likely be the sockets either side.

If a earth loop impedance tester is not available then R1 + R2 reading will need to be taken as "flameport" describes.

 

[Space cat]

I would use live and neutral because earths sometimes get tied together in unexpected ways. The socket with the lowest reading will most likely be the one nearest the join. If, when you open it up, you find it's a spur, then you have a junction box somewhere and your job just got a whole lot harder.

As flameport says, you can't rely on the highest reading if you have spurs. What you can do is repeat the test using the wires on the other side of the join. As a final test, isolate one set of wires in each of the two sockets you find and see what still works. If you've got it right, everything will work except the 'missing' socket and, possibly, the ones with the isolated wires. You will also know whether those isolated wires lead to the missing socket or back to the CU.

 

[JohnD]

remember this is the DIYnot website.

will the DIYer have an Earth Loop Impedance Tester? Will he know what R1 and R2 are?

I don't know the resolution of a £10 high street multimeter, not sure it will be good enough.

I think a workable DIY approach would be to take up some floorboards and look at the cable.

 

[ericmark]

remember this is the DIYnot website.

will the DIYer have an Earth Loop Impedance Tester? Will he know what R1 and R2 are?

I don't know the resolution of a £10 high street multimeter, not sure it will be good enough.

I think a workable DIY approach would be to take up some floorboards and look at the cable.

What you say is very true. And it is hard to advise when you don't know the skill of person your advising. However to do the work a Minor Works Certificate should be issued and although R1 loop, Rn loop and R2 loop or R1 + R2 could be used to find Zs the only way to test installation is with a high voltage ohm meter running at 500v. So without a "mega" one can't do the work. And most mega type instruments also have the 200ma low ohm range as well. The tool is required to do the work in the same way as a screwdriver and just as no one would expect people to work on domestic electrics without a screwdriver neither should they work without at least a "mega".

The Earth Loop Impedance meter can be got around and Earth Leakage Trip meters are only really required when something has been added to a RCD or an RCD has been changed. Although in theory RCD's should also be checked.

However that is never going to happen and even my Avo Mk8 would have a problem in measuring the resistance change between sockets and you are right without the meters required by BS7671:2008 only method is to trace cables.

To help those who don't have the correct meters to understand the correct meter will measure 0.01 of an ohm where a multi-meter even my Avo Mk8 has a problem in measuring anything less than an ohm. Even the digital multi-meters have problems with 0.1 ohm never mind 0.01 ohm so are not much good. With cable 2.5mm having a resistance of 0.018 ohms per meter 6 meters will just about be measured with at digital multi-meter that can measure 0.1 of an ohm it would be therefore unlikely to be any help.

 

[davelx]

Visually tracing the cable is not the only way. If you turn the power off and remove ALL the sockets and separate the cores, you can then loop L-N on each cable in turn in one socket, and use an ordinary continuity tester between L & N on each of the cables at the other sockets until you find the looped cable. Then you know which sockets one run of cable links - label/note it and repeat as required 'til you have the whole ring