DIY Doctor

Two sets of Cables Running to a Spur?

Postby jaylord79 » Fri Apr 05, 2019 8:01 am

Hi all, just a quick question, found a spur from the ring final circuit. Checked it out and it is a single spur not spurring off again and finishes at the one socket. The odd thing is it’s fed by two 2.5mm twin and earth cables from the socket before. Socket before has been removed and a blanking plate put over the backbox. Cables are all joined together in connectors. So the ring hasnt been extending but the two cables going to the spur and the two original cables are all joined together, all lives, all neutrals all earths.Just wanted to check this is ok and I don’t need to remove one of the two cables feeding the spur as don’t want to chop out the wall to remove the cable and the blanking plate has a damaged screw so cannot fully take plate off. Many thanks guys.
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Postby ericmark » Fri Apr 05, 2019 10:41 pm

I read, then re-read, and tried to think of a reason for running two parallel cables, I will guess it was intended to extend the ring, and for some reason they changed their mind.

Only reason I can think of is the loop impedance was too high, and I can't think of an easy way for you to test.

Anyway nothing wrong leaving it as it is, I was told when doing inspection and testing course we should test for a figure of 8 which is what you have, but as I studied further I could not see any real problem with it.

So with modern regulations we are permitted 108 meters of cable in the ring, it was 80 some thing, and the reason limited is volt drop, there is another reason to limit length which is the earth loop impedance, however with RCD protection that is not so much a problem.

So likely there is no reason why you can't remove one cable, but without some readings can't be sure. If RCD protected then having over the permitted volt drop is not that much of a problem, fridges and freezers can be damaged by excessive volt drop but very little else.

Have you got a schedule of test results either part of installation certificate or electrical installation condition report? If so that should tell us how close it was to the limit.
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Postby Mr White » Sat Apr 06, 2019 6:57 pm

A picture would help.
But from what you describe it sounds like the ring has been extended.
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