Extending Ring Main for Sockets While Insulating under Floorboards


Postby Ed_R » Fri Sep 11, 2015 1:17 pm

Hi - I am taking up floorboards in my home study to insulate underneath (can't stand another winter with cold feet). Thought I'd take the opportunity to spur off two more double plugs.

When I looked at the plugs first (before floorboards were up) was surprised to find what looked like one plug on ring main, and rest looked like spurs.
Now that I have the boards up I can see that someone at some point has cut into the ring main and using 30A connector strips as junctions spurred off each set of plugs (except one) and all wrapped in insulation tape on the ground underneath the joists. [In my loft I found similar when it came apart(!)]

I'd like to leave them alone - but I think they should be maintenance free junctions at least. And at the end of the day with the boards up its presumably simpler to just have a conventional ring circuit arrangements and no spurs at all.

I have traced the circuit to and from fuse box - so its definitely a ring.

It seems a simple enough task. It seems less likely to go wrong to wire it properly (and certainly less complex for the next person who needs to do something to it). And it would avoid the problem of creating inspection hatches for the junctions through the insulation. We are well away from kitchen, and bathroom. I am reasonably handy.

Any reason why I shouldn't do it?
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Postby ericmark » Sat Sep 12, 2015 11:17 am

The ring final will need testing but no reason not to DIY. The major problem with a ring final is one fault will not stop it working but can cause an over load so testing is important.

I am loathed to tell anyone I don't know the skill of to test at the consumer unit as even with power switched off there is still power there. You can test the last socket to be fitted and you will need to fit that socket very carefully to ensure no wires come off as it is put in place.

For an electrician it is easy. We have something called a loop impedance tester, so before we start we test. Then we see if there is a ring, assuming there is then when we finish the reading should be similar to start lose any connection and there will be a marked increase in loop impedance. However the meters are expensive. The Martindale EZ150 will do a loop test but the lights are not a good enough reading to show if a ring connection is lost.

Loop refers to the connection line and neutral or line and earth back to the supply transformer not anything to do with being a ring.

If the ring is really a ring and the sockets pass with the Martindale EZ150 then it is unlikely there is a fault. However the Martindale EZ150 will not catch all faults.

I was recently at my daughters, my son had fitted a new consumer unit and found a neutral - earth fault which was tripping the RCD when there was a load. His meter had failed so I went up with my low ohm and installation tester to find where the fault was. I found a caught neutral wire on a socket beside the bed touching the back box it took me around three hours slowly getting closer to the faulty socket working out with each socket removed if fault before or after that socket. The Martindale EZ150 would not highlight a fault of this type. Neither would a simple multi-meter until RCD protection these faults could go unnoticed for years.

With most accidents it is not one fault. It is a number of faults which together allow the accident to happen. This is why we inspect and test, by removing as many faults as we can find there is less likely hood of a new fault causing an accident.
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