Ring and Radial Arrangement Questions

[ebow72]

Hello all, I have mentioned in other posts I try and treat this forum as an extension of my place of work (Still awaiting work placement)

Anyway, here are my questions / queries.
Other than the area served via a ring circuit what other pro's are there for going with this method.

It seems daft to me using double the amount of cable opposed to a radial circuit.

Looking at the regs the socket arrangements look fairly similar, however I was under the impression you could never spare of a spare in a radial circuit, but looking at page 426 of the regs, it seems you can. The only noticeable difference I can see is you can't have a FCU supplying fixed equipment on a radial circuit.
Again I may be wrong, so hopefully someone would be kind enough to assist.

And this keeps cropping up and was wondering how you might go about it, if you was to extend the ring circuit would you use a junction box (accessible) or would you use a crimp and heat shrink method, providing your back boxes are deep enough? Or have I got totally the wrong idea about it. I have tried asking our tutor but doesn't seem over bothered at times...

Before some eager beaver member points out I am not qualified yet, or part p'd up, or a fan of abba, I am just trying to get as much crammed up in my tiny mind before I forget. I am not doing any work that I am not permitted to do.
Thank you to everyone who, might read or reply.

Cheers
Ian

 

[johnboy6083]

With a ring you are effectivley using 2 cables in paralell. This means that the volt drop across the circuit is halved. It offers flexibilty, and it means that you can use smaller cables to feed a load anywhere on the ring.

For example, its common practice to see a 32A ring final feeding standard 13A sockets, run with 2.5mm2
If i was to design a 32A radial, it would have to be at least 4mm2. This is nowhere near as easy to second fix, and is nearly impossible to spur from, as you cant fit 3x4mm2 in the back of a socket.

Radials are not as easy for joe public to mess up though, and are marginally easier to test.

 

[sedgy34]

Radial circuit is 75 mtrs max Don't matter about branching off as long as the cable is protected by the fuse

 

[oldtimer]

Remember the ring is a hangover from years ago when each house got a lighting and power circuit . So will they get rid of it well yes in due course it will have to go and then the 13A socket is next

 

[TJS]

The Cross sectional area on a ring final is 5mm2, and there fore much safer, to install a radial on 13a sockets with 4mm cable is difficult,

 

[Engineer54]

I can't see the demise of the ring final circuit anytime soon, it's far too versatile over a radial circuit!! Whats more, if ring circuits were to go, the standard accessory plates would also change, as they are based on the the versatility requirements of ring circuits. I can see that the terminal connection capability will be reduced to the standard now in use with the Shuko and other European outlets, where 2 X 2.5mm is the maximum you can terminate!! So no spuring/extending capabilities mid circuit, without turning the back box into a JB box ...lol!! Had this problem on a few projects, where European outlets have been specified...

All socket circuits will be a max of 16A unless single point circuits. So it will also increase the overall size of CU in order to accommodate all the extra circuit MCB/RCBO etc. It'll be a dark day, if they get rid of the RFC!! The only beneficiary i can see, will be the new wanna be electricians, ....in the form of simple point to point wiring and testing!! lol!

So don't just take things at face value, there is a can of worms waiting for you ...lol!!

 

[kingeri]

"you can't have a FCU supplying fixed equipment on a radial circuit"

Of course you can! What gave you that idea?

And don't get confused over what a spur is. On a 4mm radial, a spur use a reduced csa cable, usually 2.5mm, and hence can only serve one double socket outlet. If you branched off with 4mm then this is not a spur, it is still part of the radial, and hence can serve as many sockets as you like.

 

[Engineer54]

And don't get confused over what a spur is. On a 4mm radial, a spur use a reduced csa cable, usually 2.5mm, and hence can only serve one double socket outlet. If you branched off with 4mm then this is not a spur, it is still part of the radial, and hence can serve as many sockets as you like.

The trouble you encounter then is, getting the 3rd 4mm cable into a terminal connection, that is not designed to accommodate 3 X 4mm cables!! lol!!!

 

[mydigitalhome]

Spain, Italy etc tend to install joint boxes at high level above socket positions. It is also common practice to run radial from room to room, install a jb in each room and then star wire all sockets in room to that point. Just returned from a project in Napoli and all jb's had twisted cables to make joints and a bit of poorly fitted electrical tape no cpc from jb back to cu. 3 days to sort out before I could start work !

 

[Guitarist]

The first house I rewired had a JB above each room with spider legs to each socket

 

[ebow72]

"you can't have a FCU supplying fixed equipment on a radial circuit"

Of course you can! What gave you that idea?
Well I have been going through the regs and just off Fig 15B as I didn't see one I took it as you couldn't...

And don't get confused over what a spur is. On a 4mm radial, a spur use a reduced csa cable, usually 2.5mm, and hence can only serve one double socket outlet. If you branched off with 4mm then this is not a spur, it is still part of the radial, and hence can serve as many sockets as you like.

This now makes so much more sense now, thank you Kingeri, sometimes another persons description does the world of good. Thanks Again..

 

[Silly Sausage]

In domestic situation, rings make sense from a spacial view.
A downstairs layout, you go along one side of the house and virtually end up at the same place on the other side, may as well run the end back to the CU...hence ring.
Upstairs, almost the same, might have to run an extra 10m from the end back to CU, but all in 2.5 rather than 4mm.

Use radials for dedicated circuits.

 

[kingeri]

The trouble you encounter then is, getting the 3rd 4mm cable into a terminal connection, that is not designed to accommodate 3 X 4mm cables!! lol!!!

Very, very true eng! Unless you use a joint box or some of the MK sockets which advertise as being able to take 3 x 4mm cables (I have never attempted this....but just talking theoretically!)!

 

[Guitarist]

Very, very true eng! Unless you use a joint box or some of the MK sockets which advertise as being able to take 3 x 4mm cables (I have never attempted this....but just talking theoretically!)!

It's one thing to get the cables into the socket...It's another thing to push it back for fixing

 

[kingeri]

How very true! The physical difficulty of getting multiple 4mm cables terminated, combined with the (in my view) undersized 1.5mm cpc makes me generally stay away from 4mm for sockets.