Radial to Ring main - Junction boxes?


5 Mar 2009
Reaction score
United Kingdom
I am looking to convert a radial circuit (2.5mil) to a ring main. I understand about adding from the last socket and back to the CU. However on checking the wiring layout, it goes as follows... from the CU to 30amp junction boxes, wire continues to next Junction box and so on to last socket. Each socket is fed from each junction box a single wire (spur) goes to the socket...(instead of 2.5 wire in and out of the socket as per diagram on site).
Question: Is it still accepable to convert this circuit to a ring main, either continuing using junction boxes or 2.5mm straight back to CU? :?:
Sponsored Links
I don't think so,
I can't remember if it is a reg or guidance, there should not be more unfused spurs from on ring final than points on the ring.
div, the JB is the "point" and the socket is the spur from the "point"..

it even shows the spur from a JB on the drawing in the back of the regs..
Sponsored Links
Read 8.2.4 of the OSG - think this is what I was thinking of.

The total number of fused spurs is unlimited but the number of non-fused spurs should not exceed the total number of socket-outlets and items of stationary equipment connected directly in the circuit.

Was referring to "point" as in a place to connect an appliance such as a socket or FCU, not a JB. Never considered a JB to be a point as such.
Reading what the OP says, each JB has it's own socket, so it does not exceed that requirement ?

As long as the spurs actually only have the single socket on each one.
Yep, so each socket would be on an unfused spur from the ring via a junction box.
I don't like the idea, like I said I don't know if there is a reg against it but guidance says no.
It wont be that straight forwards to test either.
Wouldn't you create a whole ring of unfused spurs with not a single socket outlet or 'item of stationary equipment' actually on the ring? :eek: Strange installation, and as spark123 says, surely uncompliant? Can you not just run an additional 2.5mm cable from each JB to its socket, and connect in the JB so that each socket is now on the ring?


EDIT: Oh, you were quoting the OSG and not a reg. Maybe it's allowed then? Still doesn't seem like best practice.
So what do you think happens when you use power track?
In theory there is no reason why one should not have a ring main with no sockets directly on the ring main.
But in a house we have an access problem so under normal circumstances because of the rules on using any screw terminals requires them to be accessible and most cable runs under the floor boards it would not be economical to use JB's.
But I have seen where a single 4 core cable supplies the ring main and it is terminated into a series of adaptable boxes with two stuffing glands and two spurs one from feed and one from return cores all on top of partition walls and socket provided each side at intervals, single socket at end of cable. This allowed the use of 4mm SWA and a huge length over 100 meters it was designed to plug cleaners into and the wall was a good 4 meters high in a cold room and it did the job A1 and had a good ELI at every socket.
Page 362 first socket left hand side shows that method. One must remember rule of thumb or as it is now called historically was there to ensure the load current in any part of the circuit should be unlikely to exceed for long periods the current-carrying capacity of the cable and other methods are not ruled out.
There are however a few things that come to mind first is of course assess the other is if it is considered as a new circuit? By modifying it one is then responsible for ensuring everything complies. In industry when all cables tend to be on tray work or similar it is relativity easy to ensure there are no hidden spurs but with a radial one is allowed to spur off a spur however this is not permitted with a ring. For me who fitted a radial in my house which I am the only person to have ever lived in it to convert a radial into a ring is not a problem as I know every wire in the house but to go into an old house and ensure there are no hidden radials is near impossible so in a house I would not under normal circumstances convert a radial into a ring. With the exception of where it is only to correct a high ELI and after converting into a ring the fuse/MCB will remain as 20A.
Thanks for all your threads, but there seems to be conflicting views if it is safe to do so or not.

Perhaps a bit more detail might help. The premises is a bungalow and all the JB connections are in the attic space and accessible for inspection.

I estimate the main wiring 2 x power 2.5mm radial circuits and 2 x 1.5mm lighting circuits were put in about 40 years ago. All the wiring has been replaced (rubber out/ new in) keeping to the original JB connections as it was impossibe to wire the 2.5 mm power cables continously to a socket and onto the next socket as is usual.

The original set up is the radial from the CU to JB's and drops down thru the wall by a single wire taken from the JB to a wall socket. From each JB the radial continues to the next JB, a drop down cable to wall socket and so on to the last socket. The current radial circiuts has 7 sockets on oneand the other has only 3, 10 sockets in total. (The kitchen is wired separately).

I was thinking of joining the 2 radial power circuits with 2.5mm to form a ring main back to the CU. The JB set-up is the spanner in the works.

Will this be safe or should the JB be removed and a standard ring main put in, obvioulsy this would create a lot of work to get down and back up to the attic.

Can anyone Clarify all the above threads in layman terms :!: ....cheers lads.

I'm not saying it is unsafe to do that, just the guidance issued by the IET says not to.
I can think of issues from a point of view of inspection and testing i.e. it isn't a normal circuit layout so you will struggle to do the normal ring interconnection tests.
div, the JB is the "point" and the socket is the spur from the "point"..

it even shows the spur from a JB on the drawing in the back of the regs..

Have a look in Part 2 (Definitions) of BS7671:2008

Point (in wiring). A termination of the fixed wiring intended for the connection of current using equipment.

Current Using Equipment. Equipment which converts electrical energy into another form of energy, such as light, heat or motive power.
I do see your "Point" and I think it unlikely that without referring to regulations that anyone can be sure there are no more than one socket on any spur or all JB's are accessible.
But although the JB is not the termination of the fixed wiring it is no different to having an extension lead which is never unplugged except for 433.2.2 which could be quoted as there is no fuse in JB so distance from JB to socket should be no more than 3 meters.

But to recap although it could be done safely it is very unlikely to be done safely so I would recommend not doing it.

Nitty gritty we are talking about fire risk. And to me fire in the home is a lot worse than the odd belt and I would never take the chance and as to if complies or not is immaterial.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links