Tracing spur cable?

[noxfort]

Hi guys,

Was going to spur off a bedroom socket to add a socket for bedside lamp. Originally the plan was to use the double socket to the right of the bed but when I took i off it already had 3 cables. I assume this already has a spur?

I instead just used the left socket to spur from but the third cable is really bugging me as I don't know where it goes!

I disconnected it and put a connector block on the ends and tested every socket, light, bathroom extractor and all still worked fine.

Anyway I can figure out where this cable goes as my sanity is at risk. Its not even important anymore just annoying I cant figure it out!

 

[EFLImpudence]

Perhaps you have left the spur connected and disconnected one side of the ring.

 

[noxfort]

I was just sat here thinking I may have disconnected the wrong one during my test.

Is there a safe/easy way to test which ones are ring main?

 

[PrenticeBoyofDerry]

Is there a safe/easy way to test which ones are ring main?

The safest way would be to employ a competent electrician.

But failing that you would require to do dead tests on the circuit. Which will require suitable test equipment, for dead testing a multi-meter that can read low ohms resistance will do, and for voltage a two pole voltage indicator (I would not recommend a multi-meter to test for voltage, unless it had GS38 approval).
So isolate the circuit at the consumer unit/fuse board.
Prove the conductors in the socket you are working are dead.
Then disconnect any twisted ends of the conductors, so all are disconnected from each other.
Then test end to end resistance between two ends of each colour core.
So a pair of lives (whether it be red or brown cores) a pair of neutrals (black/blue cores) and a pair of earths (green and yellow)

You should only have two conductors of each L,N & E, that show a continuity reading, this should be reasonably low on each core, normally the earth would read higher than the live and neutral. The live and neutral should give a measurement that is very close to each other.

This cores will be the ring final cores, the cores that do not give end-end readings is the spur.
This will only work on a ring, if you have radial socket circuit, it will require different methods.

Please note the requirement for RCD protection for any newly buried cable within walls and newly installed sockets. Also you must follow the safe routing of cable zones, when burying cables within walls.

 

[noxfort]

I seem to remember doing something similar whilst trying to locate which cables where switched live in my lights. Obviously with that I was checking L to N and seeing which had resistance.

I have a voltage tester as I always like to check off at the mains is off before replacing anything.

I 2 rings with 32a each with 30ma RCD already and dont plan on doing any new wiring at present.

Thanks for your help.

 

[ban-all-sheds]

I have a voltage tester

What type?

 

[noxfort]

One of http://www.toolstation.com/m/part.html?p=83734

I also have a non contact pen I got on offer at screwfix. It was an impulse at the till buy!

 

[JohnW2]

This cores will be the ring final cores, the cores that do not give end-end readings is the spur. ... This will only work on a ring, if you have radial socket circuit, it will require different methods.

All true, but I would add that, provided all cables are the same size, the concept of 'a spur' doesn't really exist in relation to a radial circuit, so 'identifying which was the spur' would not have any meaning (or importance).

Kind Regards, John

 

[noxfort]

A quick update.

Managed to grab some free time today to investigate. Turned power off and used resistance test to see which two cables are part of loop.

The cable I did remove was the spur cable.

I am running out of things to check. I have a few ideas would like any further thoughts on them.

I am going to check in the loft. The cable appears to go under the floorboards but I have some unidentified 2.5mm T&E cables going up to the loft near the hot water cylinder which is in the same room.

A blanking plate in the bathroom has some crimped connectors in them. Think it was just to relocate the extractor fan isolation at some point but will check these to see if they are live with the spur cable removed.

Any other ideas I could try? Its wired in T&E with Red and Black wires so shouldn't be anything that recent.

Thanks

 

[ban-all-sheds]

Its wired in T&E with Red and Black wires so shouldn't be anything that recent.

How long have you lived there?

a) At the time of writing there are 341 sales on eBay of red/black twin & earth.

b) If a previous owner already had some cable on 31/3/2004 they are unlikely to have thrown it away on 1/4/2004 and bought new.

 

[noxfort]

Fair Point.

I have been here a year. Upto 2012 it was a council rented property built in the 1970's

Have currently got the socket removed and the ring connected with a junction box and the spur terminated into a junction box.

Have just checked using a non contact mains tester the two cables going to the loft in the airing cupboard. (It's only a meter away).

Both show no sign of live with the spur disconnected. I will connect the spur up again tomorrow and check if its then live.

If one of these wires goes to the loft from the socket it will obviously help me identify what is being run from a spur but having 2 wires go up/down makes me wonder if someone has spurred form a spur without an FCU...