Is it a ring main or two spurs?

[AndyKnight]

We dissmantled our kitchen a few days ago and found some dodgy connection block which the cooker was wired into.

There appears to be two twin and earth cables in parrallel coming down the wall in the plaster which connect to this block. A double socket was also connected to this block which I have disconnected for the time being.

Both red wires going to the block are live (230ish volts tested with my multi meter).

I have added a pic so you can see what I mean. The neutrals are joined but not the live wires.

How can I work out if these two twin and earth wires are on the same ring and whether the red wires should be joined together?

I plan to turn of the electrics and turn on each circuit one at a time and check with my multi-meter to see if either one or both are live on which breaker. Apart from that what else can I do?

Thanks

Andy

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• AndyKnight
• 16 Jul 2009
• 1

 

[SparkyFromTheValley]

first thing, be careful when playing with electric, especially dodgy wiring as shown. u could be opening a whole can of worms!

to check if they are on same circuit you need to turn the power off at the mains. then set your multimeter to ohms (checks resitance) touch the 2 red wires with the probes, if they are on same circuit you should get a reading. this only says if they are on same circuit, to fully be sure they are on a ring means taking readings at the board, which would require a long step by step walkthru which i wouldnt advise here.

 

[TicklyT]

I can see a bit of a flaw in that test if you meant turning off the main isolator for the CU. You would see continuity between two circuits connected to two different fuses/breakers.

Similar technique to above. With the supply isolated, and the fuse removed or MCB for the circuit turned off, first check there's no voltage on any of the conductors, (I was taught always to start by testing for mains voltage, to save frying your meter if something else unexpected is going on) then check for continuity between the two reds. If you see continuity, it is likely to be a ring.

If there is no continuity, test again with the fuses replaced / MCBs on, but the supply still isolated. You should then see continuity through the fuses/mcbs of the circuits.

If there is still no continuity, you may have a spur off a spur, a broken radial circuit or some other non-standard arrangement.

 

[Wooshzz99]

I hope its not supposed to be a ring considering it looks like its been split for a long time .....

 

[AndyKnight]

I can do those tests pretty easily in a bit. If the two twin and earth cables are part of the downstairs ring and the two lives are not connected together what problems does this cause?

Thanks

 

[Wooshzz99]

It means its been running as two radials for a long time.

 

[Spark123]

What sort of cooker - gas or electric?

 

[TicklyT]

The fuses / breakers protecting ring final circuits have a higher capacity than the individual cables used to make up the ring. We can only get away with this because there are two conductors in parallel feeding every point of the ring.

IIRC ring circuits were only devised in the first place so electricians could get away with using cheaper 'undersized' cables in a relatively safe way when the country was bankrupt after WW2, copper prices were sky high and the demand for electrical appliances was growing rapidly.

One problem is ring circuits are fault tolerant, and will carry on working without any apparent signs of distress even if there are faults present that would stop other designs of circuit from working and prompt investigation and repair.

If a ring is split, accidentally or otherwise, then you have two radial circuits fed from one over-rated protective device. If you end up with the full load carried by just one radial, it may lead to overheating and a possible fire hazard amongst other things.

 

[AndyKnight]

Ok, I have run some tests. The results are as follows.

I have tested the live wire of each of the two cables with a multi meter after turning on each breaker and then turning off again.

Both of the the live wires show 230ish volts when a single 32amp breaker is the only breaker in the on position. I think this proves they are on the same circuit.

I have also turned off all breakers and the main box to the off position and then used the multimeter on both red wires. This changes the ohms value from 1 to 00.1, 001 or 000 depending on which of the 5 ohm settings i set the meter to.

Is this enough to prove that both are on the same ring and the red wires should be joined together?

Thanks

Andy

 

[Steve]

Does your meter have an audible continuity setting? It might be marked with a musical note. Use this. If you get a sound, you can connect them.

However, the question then is, what are you gonna do with the wires?

 

[AndyKnight]

the specs of the meter says it has a continuity test on it. There is a picture of an arrow head with a vertical line through the head and a sound wave next to it. This is the only setting that makes the multi meter sound a high pitched beep when the testing prongs are touched together.

Woudl this be the correct setting?

Regarding the wires all I want to do is connect them and put them inside a junction box and leve them. I just want to get rid of a horrible connector block just hanging there without it having some form of protection around it.

I think originally there was another socket under the block which was removed before i moved into the house.

The old cooker i removed was wired directly into the block however all the wires in the block were removed when this happened and we can't remember whether the two lives and two neutrals were connected in their respective pairs before we removed them.

I wish we'd taken a pic beforehand!

Thanks

ANdy

 

[ban-all-sheds]

Untitled

• AndyKnight
• 16 Jul 2009
• 1

I can't imagine why someone would do that - why put the lives in separate terminals but not the neutrals? It clearly wasn't because of not having enough terminals.

I wonder what they were thinking?

 

[AndyKnight]

I have set the multi meter on the continuity setting, turned off all the breakers on the CU and set the CU to the off position.

The multi-meter has sounded an audible continious sound when hooked to both live wires.

Can I connect the two live wires now or should I test something else?

Andy

 

[Steve]

Yes, connect them together and never darken our doorway again.

only joking.

By the way you cannot simply shove them back into that hole without any warning that they are there. Cables must follow safe zones, which are marked out by electrical accessories being present on the wall.

 

[AndyKnight]

how should I handle this then? Should i put a blanking box in containing the connection so that people know there is a junction there?