Is this legal

[Comftybold]

Hello there a quick question if anyone would like to cast their view on it.
Ive been asked to do some electrical work in a laboratory i.e add some sockets to the existing bank of 10 twin sockets which are fixed to trunking.

On checking the existing sockets they are all on a 4mm radial. The incoming supply comes into the back of the trunking which is a 2.5mm ring circuit which runs about 15m down the corridor to the db. The ring circuit has no sockets connected to it, just runs to the trunking and back again. The connections for the radial to the ring is a chocolate block.
So if anyone can throw their opinion on this it would be much appreciated

 

[DJ Ovengloves]

What do you think?

 

[telectrix]

is the block accessible? does it show signs of deterioration? not ideal situation. why did they not just make the whole circuit a RFC?

 

[netblindpaul]

What's illegal about it?

 

[Comftybold]

Well thats just the helpful answer i expected. Personally i don't think it is. But these labs are all the same, in UCl buildings in london and installed by large electrical firms. So how come they can get away it?

 

[telectrix]

a sort of backwards lollipop circuit?

 

[Zebra Stripe]

Not "ilegal" you mean does it comply to BS7671 etc or is it safe

 

[Zebra Stripe]

A bit like a big 4mm spur off a RFC...I think that if the connection to the RFC is sound and accessable as Telectrix has asked, then although unorthodox (spelling) it maybe ok.....

 

[Comftybold]

Its safe as I've tested it, but i don't see any regs in 7671 in connection with that set up

 

[netblindpaul]

Well thats just the helpful answer i expected. Personally i don't think it is. But these labs are all the same, in UCl buildings in london and installed by large electrical firms. So how come they can get away it?

Don't be sarky, I asked you a question in the same way you asked a question.

If you can answer mine, then you will have your own answer.

 

[Comftybold]

i aint being sarky, just asked for an opinion, not a 4 word answer which to me was sarky

 

[amlu]

there is no regulation that will say is not legal. current carrying capacity of 4mm in trunking is 32amps. if the lot is connected to 32a breaker then it may be bit unconventional but nothing wrong with it. test as a radial at furthest point.

 

[HandySparks]

a sort of backwards lollipop circuit?

Or, looking at it another way, just a radial with the first part run as parallel cables with a total csa on each of the live cables of 5mm² (provided that they're run together).

 

[GLENNSPARK]

What's illegal about it?

exactly...

its like a hybrid...well in fact it is...but just reversed....so rather than the 4mm/1.5mm coming from the board...its the other way round....

as long as disconnection times are being met.....

 

[Comftybold]

Thanks for that, their all on 32amp breaker and also the db board is on essential supply, but much appreciated

 

[Engineer54]

Nothing much wrong with the unconventional wiring, but it's normal for ''laboratory sockets'' in schools to be a little more protected than just by RCD devices. But then again standards have fallen and continue to fall, so i'm not that surprised to be honest!!

 

[Rockingit]

My guess is that you might find that back in history the room had a few sockets on a ring, then got modified to how it is now. As others have said, if the CPD is suitable for the lesser of the cabling conventions and disconnection times/Zs for it are being met then it complies with the requirements of BS7671. It might be more compliant, however, if you swapped those choc-bloc screw terminals for something MF based instead.

Oh.....and if I were in your shoes..... I'd be wondering why it is that you've been asked to do this work instead of 'the big firms' that have been in there previously - has someone got upset with somebody?

 

[pepparz]

if its a sick bird then it might well be illegal.

 

[Comftybold]

Hello, no, the big outfits are still in there, their not interested in doing the small little labs anymore, they more or less please themselves with that.
The labs have generally 2 different supplies. Non essential which is on a ring 2.5mm and rcd protected, the essential supply which is what I'm looking at it, is a separate feed as i first mentioned.
Its just why run a ring in 2.5mm then branch off with a 4mm radial?
But thanks anyway

 

[kingeri]

If it were a 'proper' ring serving multiple sockets, with a 4mm branch coming off it serving multiple sockets, then the concern would be potentially overloading one point of the ring. What you've got there is better described as conductors in parallel for the first part. Probably!

 

[Comftybold]

Thanks for that, thats exactly it

 

[Engineer54]

If it were a 'proper' ring serving multiple sockets, with a 4mm branch coming off it serving multiple sockets, then the concern would be potentially overloading one point of the ring. What you've got there is better described as conductors in parallel for the first part. Probably!

It is indeed, provided that those two parallel conductors comply with all the requirements of a parallel circuit.