Extending a 13A ring main under a floor - suitable connectors?

If you've already got it, it's probably the best option

NT

As the 773-102 is only rated to 24A, but the ring will likely have a 32A MCB, really you should use a 222-412 wago connector instead.

Thanks - that was something which was nagging at the back of my mind.

We have RCBOs but the same principle should apply.

Cheers

Dave R

NT

Well, the RCBO is rated at 32A.

However on a ring main the load should go both ways. Unless one part of the ring fails.

Ummm....

Cheers

Dave R

But it is rated at up to 27A, so using a connector rated at only 24A makes it the weak link, after all we don't know how far round the ring this junction box is ...

Box of 222-412 ordered from Amazon.

Thanks

Dave R

NT

So, no discrepancy ...

Any given cable in a 32A ring is only sized on the assumption it will carry 20A or less at any given point in the ring.

Ditto a spur (double 13A sockets in general don't like more than 20A combined load, seem to recall possibly MK publishing a study on that).

Only if clipped in free air.

In conduit, under insulation etc it is rather less;

But should be >=20A for the installation method and conditions.

The "as installed" required rating for a cable on a 32A ring is only

The up to 27A figure assumes the cables are "clipped direct" or embedded in masonry/plaster. In reality the actual capacity may be lower.

What is an asymmetric ring? Only the installer will know where the cables go so any ring could have an asymmetric load put on it by a householder. It just depends on what he plugs in.

One with most of the sockets distributed near one end of it... Say where someone has installed a long run of sockets starting close to the CU, and then just returned the last leg from the far end, rather than distributing the load on the way out and the way back IYSWIM.

Well we are talking about someone modifying the wiring, not just normal use. So hopefully the installer will have some clue. If they were unsure, then upping the terminal capacity to the higher load version would be a sensible mitigation.

It doesn't really work though. You have to assume they will not plug high power loads into sockets that may be at one end but there is nothing to tell them that they are at one end. Its easy to abuse a ring and not even know.

My ring is fused at 20A so can't be abused. It doesn't have to be a ring then so if it goes faulty it won't matter. Rings do go faulty and its just about impossible for 99.99% of users to know it has.

You really have to disconnect it at the CU and meter it to find a fault although you may be able to find it with a clamp meter if you have enough free cable at the sockets.

Neither option is going to be any use to most people.

Maybe its time the standards for CUs to included test points that disconnect to ring and allowed you to test it without exposing any mains.

They do this on telephone lines in exchanges, not that you need to with the automatic test network we supplied.

Upping the terminal load is the way I am going - I assume from "should be OK" to "are you sure you need that much?". :-)

Cheers

Dave R

I think we have done this discussion before.

Ring circuits were a clever & good idea. Too bad so many people just don't understand them.

NT