DIYbanter - View Single Post - Extending a 13A ring main under a floor

Dennis@home

On 08/06/2019 09:20, wrote:
On Friday, 7 June 2019 15:32:38 UTC+1, dennis@home wrote:
On 07/06/2019 13:01, John Rumm wrote:
On 06/06/2019 20:47, dennis@home wrote:
On 06/06/2019 18:46, John Rumm wrote:
On 06/06/2019 12:48, Andy Burns wrote:
David wrote:

The box has 3 * 2 wire 773 connectors which are yellow plastic.
773 should be good for up to 2.5 mm and 24A so presumably are
suitable?
Can someone please confirm?

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.

The "as installed" required rating for a cable on a 32A ring is only
21A, so in general 24A should be ok, unless you are aware of specific
reasons why it should not be (say the joint was at one end of an
asymmetric ring)

What is an asymmetric ring?

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.

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.

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.

.

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

NT

Oh they are easy to understand, but their main reason for existing is no
longer valid.
We don't need to save copper any more so we may as well do the job
correctly and never have breakers rated above the load a cable can take.

All the arguments about them being more reliable and still working if a
fault develops are the problems not solutions.

Anyway we have had this discussion before.