is there a minimum number of sockets on a radial

[neilyboy]

Fault finding today,
no continuity on a FRC turns out to be 1 complete leg of the ring is simply not there. cant run new cable in due to decor/tiled floor
I was going to split the remaining sockets into 2 radials which would mean 1 radial with 3 sockets and 1 radial with only 1 socket
this sound ok ? going to use 16a mcb for each and put some form of note next to CU

 

[SJD]

If you saw two cables into a B20 or B16 MCB, you wouldn't assume it was a ring just because there are two cables, because if you are the assuming type, you'd expect it to be on a B32 MCB. Though of course it could be ring with a lower MCB value e.g. due to cable derating.

 

[brianmoooore]

"Assumptions" are not a good idea for an electrician that ever hopes to draw their pension.

 

[Simon47]

Depending on installation method and availability of breaker, you could probably use a 25A breaker.

 

[Mike Johnson]

Not sure about UK, but is there a maximum number of sockets for a radial as in France: eight in 1.5 on 16amp MCB, or twelve on 2.5 on 20amp MCB.

 

[brianmoooore]

No number limit, but (used to be?) an area limit of 25m2

 

[thetorrancee]

For a radial socket circuit, the size of MCB used should be no more than 16 amps.

 

[pc1966]

For a radial socket circuit, the size of MCB used should be no more than 16 amps.

In the UK it can be 32A (or more, as in the case of a 45A cooker switch + socket) and for many sockets, as we have fused plugs (typically 3A, 5A or max 13A fuses).

 

[pirate]

OK, I'm confused here.
I see that you can have "big" radials, for a cooker, for example, but for a radial socket circuit often run in 2,5mm (rather than 4mm, say) wouldn't you protect such a circuit at 16A or 20A?
I ask this, as a non-electrician, as many of you are aware. I have today installed a radial, or more specifically a radial with 2 branches, purely to serve 2 roller shutter doors which actually come with moulded plugs. The installer has specified a socket for each door, so they can simply plug the door motors in when they have installed the doors. I decided simply to install 2 single sockets, at the very high level specified, so no-one will plug in a welder etc so this circuit will be dedicated to the doors, and labelled accordingly. My intention was to put this circuit on a 20A breaker, but as an interim measure it is spurred off a double socket which is a radial on a 32A breaker. When we get the new board I will have spare ways, so the problem will be solved due to the extra ways. It's not the most critical problem, but I want it to be right. Unfortunately, when the Council installed the system to this building, they fed it from an adjacent building with SWA to trunking and then to a tiny 6-way board which has a 2-module RCD and only 4 ways free, and they didn't fit an isolator. In order to give us some power, they fitted one double socket, on a radial, off a 32A breaker, and two light fittings on a 6A.
Our intention is to get an new all RCBO board with 8/10 ways and an isolator, so we can install CCTV and other "stuff". Temporarily, the doors will be fed from the double socket spur. There is very little power usage just now, but we will move the doors to a separate breaker and wire the extra sockets we require from the new board, probably as a 4mm radial on a 20A as the space is quite small.
Sorry, that was long-winded! The doors come with moulded plugs with 13A fuses. The radial serving them is 2.5mm, so I thought that would be fine on a 20A breaker, just in case someone used the circuit for something more "heavy-duty".

 

[James]

2 sockets high level for doors on a 16 or 20A breaker is just the solution I would install, remember the rcd unless you have a risk assessment to remove the need.

 

[pc1966]

OK, I'm confused here.
I see that you can have "big" radials, for a cooker, for example, but for a radial socket circuit often run in 2,5mm (rather than 4mm, say) wouldn't you protect such a circuit at 16A or 20A?

Yes.

My earlier point is that for UK fused plugs you can feed the sockets with anything above 13A (within reason) limited only by what the cable needs for fault and overload protection (and said cable fits the terminals of the sockets OK).

So you could put in a single (maybe a double) socket on 1.5mm on 16A, but probably a poor idea.

Or as many as you want in 2.5mm on 20A subject to expected normal total load being below 20A (usually the guidance on area 25m^2), or same in 4m/6mm on 32A for bigger area (but then RFC starts to look more attractive), or it could be a single socket part of a cooker switch assembly on 10mm with 45A or even 50A MCB.

 

[brianmoooore]

A general purpose 2.5mm2 radial circuit, serving sockets, would usually be fed by a 20A MCB, assuming poor design hadn't reduced the current carrying capacity of the cable below 20A at any point.
The current taken by a roller shutter door is usually a very few amps, so absolutely fine to share with general purpose sockets.

 

[pirate]

Thank you all for your responses to my query, much appreciated.
I just reckoned that the moulded plugs on the doors will be fused to protect the cable downstream, and I wanted my installation to be protected in the same way.
There is RCD protection at the board, and I designed the circuit to avoid any down-rating factors, so it is all clipped direct to the brickwork. We have a door and a couple of windows where the cable runs over, so as I said it is all clipped direct with fire-clips all the way.
The single sockets at ceiling height should preclude anyone plugging high-load items in, and the labelling should too.
If anyone should do that, then they are a bit silly...and would have to unplug the doors, which is why I specified single sockets.
Thanks again for your contributions, I really appreciate your help.
I should mention that I only do the donkey work...we have 2 electricians who will check and do the final CU connections/certifying...which is easy as most of the wiring is visible/accessible.
Thanks to all of you again who have contributed and provided positive feedback.
Just for fun, I can tell you this is a charity place I do work for, and while 2 of the walls are easy to wire due to nice straight mortar lines, one wall is hard concrete and a bu**er to drill! The laser is your friend, for sure! Oh, and a decent SDS drill!
Anyway, tomorrow is "connect"day, so much less manual labour and more nice stuff for me.
BTW, those Linian clips are amazing!

 

[pirate]

Tiny update...I returned today to do the final connection. 2 branch radial into adaptable box, feed to this from the previously installed metal-clad double socket. I glanded everything, then went to tap off the socket, and there was no earth from the back box to the face plate (despite the original label being in there saying it must be earthed). Basically, the grub screw was missing from the back box earthing terminal, so it had just been left without that fly lead. I will get a new back box tomorrow as I didn't have a suitable screw, but I put a fly lead in by inserting it through the terminal and twisting it tightly into place as a temporary fix. Meanwhile, I had to open the adaptable box above which diverted the socket circuit and lighting circuit singles, and found that the N cable for the lighting had been dragged across the bush to the existing metal conduit so that the cable had its insulation almost, but not quite, stripped away at the point of entry. Given that this is a building which the charity rents from the Council (who also installed the CU) I think I will have to renew the lighting circuit as it passes through 3 or 4 more metal junction boxes to feed the luminaires. Not a huge job, but sad that this brand new installation has these problems. It would have been so simple to do properly...

 

[brianmoooore]

It's not a change that I agree with, but there is no longer a requirement for the earth flylead, as long as at least one of the fixing lugs in the back box is fixed and not adjustable.

 

[pirate]

I hear what you say, but am still of the opinion it is best practice...and to ignore manufacturers instructions is not my preferred option. It takes no time, costs nothing, and is an extra safeguard...just my opinion, of course.
The particular socket in this instance is a metal-clad, surface mount with no metal conduit to act as CPC. Also, the extreme diyers at this charity place would happily take a faceplate off while live...horses for courses.