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]

Interesting.......

What rating was the shower?

I don't think that qualifies as "8mm" CSA either - volt drop etc applying to both cables individually.

Don't think I'd be very happy with that somehow.

 

[Adam W]

I've heard of it done before, in fact I remember this scenario being discussed at college. Theoretically it would be ok - not much different to a ring.

 

[david0173]

Hi its a 9kw shower .Was not happy with it.going back tomorrow to do the job think i would be happier rewiring with the proper cable.

 

[accordfire]

The problem with it really, is that if one side develops a fault, the remaining cable will be underrated.

The end user might never know either, until it causes a fire.

That shower's calling for about 39A off the top of my head, and a 4mm CSA T&E is rated only about 36A or so, given its likely installation method.

 

[telectrix]

agree with accordfire. not good practice as stated. 6mm up to 20m run for 9.5kW

 

[Adam W]

The problem with it really, is that if one side develops a fault, the remaining cable will be underrated.

The end user might never know either, until it causes a fire.

That shower's calling for about 39A off the top of my head, and a 4mm CSA T&E is rated only about 36A or so, given its likely installation method.

You could say the same about a ring final.

 

[Adam W]

Check out 523.8 'Conductors in parallel.'

 

[davelerave]

not sure on rules -but 'paralleling' certainly best avoided on domestic final circuits

-for obvious reasons

usually paralleling is distinguished from ring finals afaik

 

[accordfire]

You could say the same about a ring final.

I guess ring finals get better press because they're "unlikely" enough to be carrying sustained current at or over cable rating - though I wouldn't like to stake money on the these days.

Ring finals, ISTR came about way back in the war years as a way of saving copper. Most original rings were simply two 15A radials bridged together - fuses and all. That with double pole fusing would have been four fuses per ring....

Looking at the typical current consumption in the UK today, it brings to mind the very many arguments over the years whether or not we're better off with 20A radials again. Depends on the job perhaps.

 

[Spudnik]

OT i know, but im just starting two small cottages.

The lounge will only have three sockets, which will be on a 20A radial.

 

[SirKit Breaker]

seen it on a cooker circuit before, 2 x 2.5mm T&E runs paralleled up.

 

[AlanWirral]

OT i know, but im just starting two small cottages.

The lounge will only have three sockets, which will be on a 20A radial.

We were discussing this in college just this week. Apparently no 'Proper' sparks use ring finals anymore. Ring for the kitchen and a 20 amp radial for both upstairs and then downstairs then using RCBO's for each circuit in a non split load board. As long as the cost isn't too much i'll be looking into this for the first rewire i do when i hopefully start on my own.

 

[Mr.Si]

It's interesting isn't it, how the UK seem to be one of the only placed where Ring Finals are still used for Sockets, whereas the rest of europe go for the Radials... I can't remember why, but we also touched on this at college. It's some sort of historical reason though.

I wonder if the UK will ever fully change to "harmonise" more with the rest of the EU.

 

[IQ Electrical]

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

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'.

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!

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!