A Broken Ring!!!

Jabbajaws · Jun 8, 2009

This may sound rather a strange question but its something that l need to understand. If a ring circuit, through a fault condition, or even by poor design, ended up becoming two radial circuits on a 32A MCB protected circuit, is there an actual danger present?

Although l know that this is not permitted in BS7671, im not sure of the reason why. Can anyone explain if this is actually dangerous, or if it is something that merely isn't permitted by the regs. Wouldn't the protective device still operate?

Thanks, Jabbajaws

Guest123 · Jun 8, 2009

Hi.

Simple reason being that a 2.5mmT+E is not able to carry 32A as a radial. Depending on where you look and with regard to various factors etc it's around 27A

Check out the CCC tables in BS7671. A 2.5mm should never be on anything more than a 20A radial.

Mr Mark Sparks · Jun 8, 2009

as lenny says 2.5 takes 27 amps max and now with all the correction factors that could be as low as about 13-14 amps
cables burried in insulation for more than 500mm of their run the ccc is halved

jellen · Jun 8, 2009

just asthe guys above say, it's all down to the current rating of the cable.

Kind of going off topic here, but i remember a few years ago hearing that Ringmains were going to be phased out due to this problem??? anyone else heard the same.

(It could just have been me having a strange dream of course

)

ecclescake · Jun 8, 2009

jellen said:
just asthe guys above say, it's all down to the current rating of the cable.

Kind of going off topic here, but i remember a few years ago hearing that Ringmains were going to be phased out due to this problem??? anyone else heard the same.

(It could just have been me having a strange dream of course )

I did my 17th a couple of weeks ago and got told the same.

scotsparky · Jun 8, 2009

Thats the roumour

stretchyboy · Jun 8, 2009

For years we all laughed at the "Spanish" style of wiring when we went on our holidays and yet we are nearly there now .................. all baring the double pole mcb's

Spudnik · Jun 8, 2009

jellen said:
Kind of going off topic here, but i remember a few years ago hearing that Ringmains were going to be phased out due to this problem??? anyone else heard the same.

They have been going to do this for a long time.

Same ol' story every year.

trix · Jun 8, 2009

All down to cenelec I'm afraid..

On the subject of a broken ring, apart from the high cpd for 2.5mm t&e, what about the dangers of

live conductors where the fault is...

Further investigation would be required, as this situation is not acceptable.

It doesn't take a brain surgeon to find, even though it may take time, but once found can be rectified.