New house ring main survey

[Benway]

Just moved into a new house. While decorating I've had to take some of the plugs/switches off the wall and noticed a lot of the sockets have only one cable, some have three, other two. What the usual way of finding what goes where?

Isolating everything at the CU, disconnect everything from the backs of the sockets, then getting a trusty multimeter on the ohms setting?

Or is there some other way that I'm over looking?

Cheers

 

[ColJack]

turn off the power, at every socket with 3 sets of wires, seperate them into terminal blocks and turn the power back on ( unplug the telly, washing machine etc first ).
now check for live at the wiring..
if you have 2 sets that are live, that's the ring..
if you ony have one set then it's a radial and that's the feed..
the one set / sets that isn't live is a spur..
the sockets that no longer works is the socket that the wire feeds.. ( plug in tester or just a table lamp will do in a pinch )..

 

[Taylortwocities]

That's good info but only do one socket at a time.

If you disconnect several sockets you will break the circuit and will not find any lives further round the ring!

So, do a socket per the above, note what is what, then go on to the next one.
Personally I would disconnect the cables at the consumer unit and do a continuity test first to determine if it is actually a ring. Then I would connect up a nice loud bell across live and earth and test like that. Then you haven't got to go back to the board and keep turning the (dangerous) mains voltage back on.

 

[mbga9pgf]

That's good info but only do one socket at a time.

If you disconnect several sockets you will break the circuit and will not find any lives further round the ring!

So, do a socket per the above, note what is what, then go on to the next one.
Personally I would disconnect the cables at the consumer unit and do a continuity test first to determine if it is actually a ring. Then I would connect up a nice loud bell across live and earth and test like that. Then you haven't got to go back to the board and keep turning the (dangerous) mains voltage back on.

Can you disconnect wires at the CU without pulling the supply CB?

 

[ColJack]

That's good info but only do one socket at a time.

oops, did I miss that bit off? sorry..

So, do a socket per the above, note what is what, then go on to the next one.

after re-connecting the one you just did of course..

 

[Benway]

Cheers for the ideas.

Once I escape flat pack hell I shall report my findings. Including if I ever find where the room stat cable terminates because it isn't at my combination boiler....

 

[Lectrician]

Why encourage someone to work live?

With everything off test between the three cables - the pair with continuity is the ring.....simples.

 

[Johnmelad502]

Why encourage someone to work live?

With everything off test between the three cables - the pair with continuity is the ring.....simples.

What if it's not a ring?

I thought testing live was different from working live?

 

[ericmark]

Even for an electrician it can be hard work tracing cables. My daughter had a dead socket and it seemed to be radial or spur. Tracing back we got to above consumer unit and still could not find where originally powered from.

I will guess that the consumer unit was in the garage and when the garage was converted into a room it was moved and likely there is a harness of cables between the two points. But only a guess.

This does show how wiring can be non standard and how testing can be a problem. Many houses will have had years of DIY and not uncommon to find double ring mains where a ring has been extended and then the original ring reconnected an a figure of 8. I have also seen 4mm 32A radials where some one has thought it was a ring and have split and extended with 2.5mm instead.

I have even found a ring supplied by two 32A MCB's one each end of the ring.

Often one can see when testing the earth loop impedance how the figures slowly increase and decrease as one follows the likely route of the ring and a marked increase with every radial.

But to test the ring it does need a meter and needs to be done dead. Main reason is that earths as well and live and neutral need testing and it is not uncommon to find a ring for two cables but third is open circuit.

So unless using an earth loop impedance tester all tests are carried out dead. The only other live tests are for RCD and polarity.

Although a spur should not be taken from a spur a radial has same type of wiring. A spur is defined as "A branch from a ring or radial final circuit." but I would not expect the DIY man to understand. If one branches with a cable size able to take the full power permitted by the supply protective device than it is a radial so from a FCU it is a radial and you can add as many sockets as you like. But if the cable is not able to take the full current permitted by the supply protective device but relies on the demand protective device then it is a spur and is limited to 3 meters and a single outlet. (Single outlet includes double socket)

Benway asks how to find what goes where. And does not ask how it is tested. And to instruct how to do live tests does not seem to answer the question! Because of the problems with twin feeds tests need to be single MCB/fuse. First I would switch off all and confirm all is dead. I have had a house where some one drilled through wall and connected to next doors supply. Then switch on one MCB or fit one fuse at a time find what it feeds and switch it off again. Repeat with all MCB/fuse and note if anything comes on with two different MCB/fuse connections. Also note if anything does not work with any single MCB/fuse but does work with two or more MCB/fuses this will sometimes high light ring main faults.

As to your thermostat likely it was connected to the motorised valve not boiler and once it has activated the valve then the valve turns on the boiler. When the combi boiler was fitted then the motorised valve would have been removed and the two cables joined at that point. Likely it was in an airing cupboard and it you look where that was likely placed you may find a connection box.

I am typing this in what was an airing cupboard which was extended into landing and had a window put in to make it a box room which was at one point used as bedroom. Now an office. So sometimes you need to visit neighbours or use some imagination as to what the house originally looked like.