new to me

[david0173]

Hi all
I came across this today ,new to me .Replacing a shower and it was supplied by 40 amp mcb with 2 lengths of T&E 4.0mm parallel wired .I had to look twice, anyone else seen this before or am I just the lucky one

 

[accordfire]

The ring circuit came about due to an acute post-war copper shortage and has been with us ever since.

Yeah - this is what I was saying in my earlier post. The idea, initially figured in '42 or so, was that it would be a way of saving copper as current demand increased - it would be cheaper to bridge two parallel circuits, making a 30A circuit which could handle higher load, than to run in new radials.

Reading some of the reports from the draft meetings for what would become BS7671:2008, I think it came reasonably close to being removed as a 'listed final circuit'.

It has been a "discussion" as long as I can remember, and learning during the 15th.

The main problem is the lack of knowledge of the correct testing procedures-I teach a 2391 pre-exam revision class and this very subject visibly ages me!

Design procedure too. Perhaps design mentality is a better expression here. In terms of pure safety, a 20A radial must be inherrently safer than a ring final. If a fault develops on the circuit, the circuit goes, end of.

Of course, it probably also means a rethink in design terms about how much current is likely to be drawn on any given circuit, and hence cable sizing, cable runs, distribution, and so on. There is a lot of "slack" given due to the fact that with a ring final, higher load is acceptable.

Presumably, there's also the implication of cost - especially in larger installations - viz. more DBs, more circuits, more cable, more everything.

I'm guessing that t&I in general is what ages you? Or do you mean specifically the testing of ring finals (or radials)?

I think we're some way away from full harmonisation, we retain ring finals, reduced c.s.a. c.p.c.'s and the BS 60439-3 UK annex enabling us to use BS3036 fuses with miniscule short circuit capacities!

Hmm. I don't know that harmonisation with Europe is necessarily "better" than what we have now, overall. I'd probably be more of a fan of seeing Europe adopt some of our practices as well as us theirs. I have no problem in general with harmonisation, where it results in safer installations.

I take your points well though, and agree, we could do a lot to be even safer than we are.

 

[IQ Electrical]

No, 100% harminisation is not better, I realise that every time I plug an appliance into the 'hole in the wall' that the continentals call a socket!

Imagine replacing our vastly superior BS1363 accessories!!

On the other hand, I spend most of my days doing Periodic Inspections and out of the many broken ring finals that I've found over the years, I can honestly say that I've never seen damage or injury caused as a result.

I suppose if you take the current carrying capacity of 2.5mm cable along with the fact that loads are normally fairly evenly spread (by nature, not design) then that would explain my findings.

I just wish a little more time could be spent on those 3 simple steps in Guidance Note 3 and I can promise you that that alone would vastly improve the pass rate of 2391-10.

 

[accordfire]

No, 100% harminisation is not better, I realise that every time I plug an appliance into the 'hole in the wall' that the continentals call a socket!

Imagine replacing our vastly superior BS1363 accessories!!

On the other hand, I spend most of my days doing Periodic Inspections and out of the many broken ring finals that I've found over the years, I can honestly say that I've never seen damage or injury caused as a result.

I suppose if you take the current carrying capacity of 2.5mm cable along with the fact that loads are normally fairly evenly spread (by nature, not design) then that would explain my findings.

I just wish a little more time could be spent on those 3 simple steps in Guidance Note 3 and I can promise you that that alone would vastly improve the pass rate of 2391-10.

Yes, and I think you've hit an especially relevant nail on the head there - its education, not just of what Guidance note 3 says - or the standards, or any other publication - but of adopting a mentality that encourages us to LOOK and READ these things and to seek them out. Don't get me wrong, I know a lot of guys do. It should be second nature to everyone though. Maybe that means that standards and supplementary notes need to be more accessible, I don't know.

 

[AlanWirral]

I thought the Ring was because of the heaters of old?? ie the reason why socket outlets are 13A.

 

[IQ Electrical]

I thought the Ring was because of the heaters of old?? ie the reason why socket outlets are 13A.

The copper shortage was the reason for the ring configuration, the ratings were calculated to allow 6kW (2Xheaters) of heating to be used in a property, along with a few smaller appliances (Sky HD, Bluray etc)