Have the rules for ring mains changed over the years?

[davesparks]

Adding an insulated layer to a dead conductor who's sole purpose is to detect a breach of the dielectric barrier within the run of cable is nonsensical from a safety perspective let alone an additional increased cost. Hence, there is a very good reason why we do not sleeve the CPC throughout the entire cable.

Yes there is a very good reason we don't insulate the CPC in T&E, in fact there are 2 reasons.
1, it's cheaper to manufacture
2, it would make the cable bigger overall and that is undesirable.

The CPC doesn't have a sole purpose of anything, it has more than one purpose.

I'm not following with your idea that the CPC is there to detect a breakdown in the dielectric barrier, could you expand on this please?
If this was the case then surely a metal tape/foil would be included in the cable which emcompases the insulated live conductors? In a T&E cable the bare cpc would only be capable of detecting this for a small part of the dielectric barrier wouldn't it?

Plus monitoring equipment is never installed to make use of this function of the CPC that you suggest.

 

[davesparks]

I've obviously seen radials but they are the odd one out of a thousand - my point was (put badly, yes) that the design choice for the main power is always a ring.

I still find this surprising, all of the installations I work on have both rings and radials used where suitable for general use power.

Recently I've even had a job where I converted 2 radials into 1 ring circuit as the radials just couldn't supply the required power for the evolving use of the offices.

When designers are putting 2 sockets on ring finals, when said sockets are literally going to be used to run nothing but a hoover now and again, i question the competency of the designer.

Undoubtedly that is lazy design but I wouldn't call someone's competence into question over it!
If its a large installation then that kind of lazy design work may be a result of over-reliance on software for design.
It could also be a general spec put in place by someone higher up that makes it more cost effective to install a ring.

 

[littlespark]

I must be a bad designer.

When i converted the back of my garage to a utility room, i put in a 32A rfc for a washing machine, tumble dryer and one double socket.... For the sake of a few inches of cable between the two isolator switches, and the hassle of wresting 2x 4mm's in the back of a grid switch.
I chose rfc over radial for that particular circuit where either would have done, purely for my own selfish needs.

 

[nicebutdim]

Undoubtedly that is lazy design but I wouldn't call someone's competence into question over it!
If its a large installation then that kind of lazy design work may be a result of over-reliance on software for design.
It could also be a general spec put in place by someone higher up that makes it more cost effective to install a ring.

A colleague once mentioned that completing their design qualification was both a waste of time and also a real eye opener where choice of circuit design was concerned. Primarily it helped them understand why certain choices might have been made, where previously they could ascertain no logic.

At my age it's likely not something I'll ever bother completing, but that comment has stuck with me and has since prompted me to try to look at circuit design from many more perspectives than before - admittedly, many choices still appear to make little sense

 

[davesparks]

The same logic can be applied to parallel feeds. They are not necessary but if you have every had the misfortune to try and wrangle cable like 120mm and above you would be cursing the designer for not use two that are not quite so " anaconda on ------" to deal with.

The worst case of this I have seen is the feed to the dimmer room in a theatre.

400A supply via a 400mm 4 core SWA, one of many questionable electrical design decisions in that theatre!

 

[Mike Johnson]

Those UK electricians with OCD would love the French staggered RCD and MCB's connected together with a staggered busbar, it is very neat, even vertical bus bars to connect RCD's above each other in different rows.

The only thing I can think that could be a compromise on UK plugs, if using a mobile appliance when you reach to limit of the cord It puts a strain on the connection, plug and socket, in the French flat plug it just pulls out of the socket and stops the machine working, would seem a bit safer.

 

[nicebutdim]

Those UK electricians with OCD would love the French staggered RCD and MCB's connected together with a staggered busbar, it is very neat, even vertical bus bars to connect RCD's above each other in different rows.

Pictures?

 

[Mike Johnson]

Been looking, but I can't find my L'installation électrique - David Fedullo , Thierry Gallauziaux will have another looks later.

 

[Mike Johnson]

The picture on the front of this book illustrates the idea: Installer ou rénover un tableau électrique - Thierry Gallauziaux ,... - Librairie Eyrolles - https://www.eyrolles.com/BTP/Livre/installer-ou-renover-un-tableau-electrique-9782416004360/