Is this Radial Circuit odd?

[doni]

Just trying to plan how the electrics are currently set up in my property.

I have identified the ring main serving most of the sockets, and how they flow together by shutting off the mains, removing every socket, and doing a resistance test after connecting neutral to live, tracing each socket until I get to the CU. That's fine.

Following another "pair" of wires from the CU, I initially assumed was on a ring, but tracing the flow in a similar manner reveals that one cable feeds two sockets, and the other feeds a single socket then a small heater in the bathroom. This is protected by a 15a fuse and supplied by 2.5mm cable. I have to upgrade the CU anyway, and will probably create a second ring by completing the two radials, but is it odd to have two radials going off separately from the CU?

 

[1john]

Why make it a ring final circuit, what benefit will that have? What happens if you make a break in a ring final circuit?

 

[ajrobb]

Just get each branch on it own circuit in the new CU.

It is not odd to have two radials fed from a single fuse. Consider, if you convert to a single ring final circuit, you will be limited to 32 A as you cannot connect sockets to a circuit bigger than 32 A. If you separate the existing circuits, each with their own 20 A CB, you get a total of 40 A between them.

Another point, if you have a ring final circuit, you are limited to each unfused spur only supplying a single socket (albeit double gang). With radial circuits you can have branches with multiple sockets. So what you already have is a radial circuit with two branches.

With a ring final circuit, it relies on design and load distribution to avoid overloading a single leg. This is not an issue with radial circuits.

 

[doni]

Thanks guys.

1john - I assumed that it would be better to have ring, and assumed that this "set up" was a bit odd, but ajrobb said it wasn't odd. Not sure why you asked your second question, but obviously a break in a ring would get me what I have now on these two radials.

 

[1john]

You are right, thats exactly what you get, but more to the point, you get a cable that can carry a max of 20A on a 30/32A fuse.

 

[doni]

Hi John - I get the point, but that's the case for every house in the country pretty much isn't it? If I complete the ring, why would I expect someone to break it? If it remains intact, a ring has a heavier load capcity doesn't it - that's what I assumed would be the main advantage of me completing it ...

 

[ajrobb]

The ring is ONE circuit with a distributed capacity of 32 A. Two radials are TWO circuits, each with a capacity of 20 A - total 40 A. Which has more capacity?

 

[plugwash]

The radials have more total capacity but depending on where the load is the ring may have more useful capacity.

 

[ajrobb]

Unless a ring is reasonably designed, it might be possible to overload one 20 A leg with a badly distributed 32 A load. A radial doesn't share that weakness. OK, with a typical distributed load, it won't be a problem.

 

[echoes]

Unless a ring is reasonably designed...

Oh no, not the 'r' word. I can't take it any more. Make it stop. Nurse? Nurse?

 

[1john]

Just remember, when you DESIGN the ring circuit, the loads have to be spread evenly, it is no good leaving the dist board and going 4m to the first kitchen socket, heading around the kitchen and then doing the rest of the ground floor, this would put the high demand of the kitchen on one leg nearest the CU. Then there is the testing of the ring final circuit....... flipping day out compared to a simple r1r2 and a insulation resistance test on a radial circuit.

 

[doni]

OK - Current position is thus:

Originally had two radials, ring, lights, day immersion heater, cooker and shower = 6 circuits (the two radials are on one fuse). I was planning to cut out some sockets on the ring, but keep the ring intact by running some 2.5 between the sockets that I want to keep, but this would involve running about 9m of cable. It would be:

A. CU - S1 - S2 - S3 - S4 - 9m - S5 - S6 - S7 - S8 - S9 - S10 - CU

The first S1-S4 are about 6m from the CU, The furthest socket is S5-S7, and S8 - S10 is about 8m from the CU on the other side. S5 is kitchen socket above worktop, S6 is likely to be a fridge. S7-S10 are lounge/hall sockets. S1-S4 are bedroom sockets.

The Radial are :

B. CU - S1 - S2 - S3

S1-S2 are bedroom sockets
S3 will feed a washing machine

C. CU - S1 - S2 - S3 - S4 - S5 -S6

S4-S6 are kitchen sockets above worktop
S1 -S2 are bedroom sockets, S3 is TV socket.

NOW - taking on board some of the comment on here, and thinking about whether I really wish to complete the ring with 9m of cable, I could just leave things as they are without completing the ring, therefore I'd have four radials, Cooker, Shower, Day Immersion Heater, and Lights - that would be 8 circuits.

What do people think about this - is it too many radials? Should I combine them to have a lower number of radials and no ring, or continue and complete the ring as I planned?

 

[ajrobb]

You might be going for rather few sockets. There are OSG recommendations for minimum number of double-gang sockets in different rooms. FYI
living room: 4-8
dining room: 3-5
single bedroom: 2-4
double bedroom: 3-5
kitchen: 6-10
hall: 1-3

The lower numbers are for smaller rooms (up to 12 m²) and the higher numbers are for larger rooms (over 25 m²). Additional sockets should be allowed for home entertainment and computer stations.

 

[doni]

Thanks AJ - one double bed, and two singles, kitchen and 1 reception. The sockets are at the lower end of your list, but the rooms are also on the smaller side (it's a flat), but I'll take another look at my plan to see if I should include some more ...

 

[1john]

Removing sockets?? whatever next.... do we really need a light in every room