Ring mains

[Sneezy]

If I understand correctly, a ring main is a ring of wire on which sockets (and spurs) are strung? Wire comes from the fuse board via all the sockets and returns to the fuse board? My question is, "why are they used?".

I asked a while ago about installing a cooker point when the fuse board is old. An electrician has now fitted a cooker point and replaced the fuse board with a nice new one. He wasn't happy about the wiring - something about the circuits being radial. I've had a look at the wiring - it's all visible and traceable (well most of it) down in the cellar. The circuits are (from memory):

Double-socket x2 in kitchen area - each on a separate wire Cooker point - including single socket Single (unswitched) socket in living area - on a separate wire but a wire comes from the socket to a juction box that feeds a second single socket in the living area, plus a single socket in the cellar (screwed to a shelf under the gas meter - I initially thought someone had balanced it there) Single switched socket in the living area Light in the cellar Lighting - only one wire but I can't be sure it's lighting because it vanishes into the wall cavity. If so, it powers all the lights both up and down stairs Double-socket in bedroom - can only guess at this but there's only one wire left :)

Each wire/circuit appears to have its own fuse - the old fuse board must have doubled (trebled) up on wires to fuses. There are no return wires.

To my mind it's all positive - much safer (less load per circuit), easier to identify problem devices that are blowing a fuse, and no chance of a blown fuse taking out, for example, the supply for one floor (like you get in modern houses). So why was the electrician unhappy?

Thoughts?

[John Rumm]

A ring is used because it allows you to have a decent number of sockets on a circuit without needing to use a very heavy (and hence difficult to route and install) cable to feed them. Typically rings are wired with

2.5mm T&E, but since there are two paths round the ring connecting each socket to the "fuse board" (or consumer unit as it is more commonly known these days) you have an effective cable size of 5mm.

Needless to say 2.5mm cable is much easier to work with than 4 or 6mm cable.

There is nothing in itself wrong with a radial circuit - they can still be used (and many countries still only use radials).

Judging by the description however it sounds like a pretty old instalation. Hence there may be a number of areas in which the wiring would not be considered up to scratch by modern standards.

[snip]

That was quite probably how it would have been wired... this can also be another limitation of radials - with a modern house that would have loads of sockets (possibly even a 100 or more) in total, you would end up with an unmanageable number of wires to take back to the consumer unit (CU), and for that matter, too many for the number of ways in a sensible sized CU.

What you say is true, in the sense that the arrangement you describe is "simple". The main difficulty is that for most modern houses the number of sockets this instalation has, would be considered hopelessly inadequate. This would in turn be likely to lead to loads of trailing leads, and multi plug adaptors being used in order to get enough sockets. There is also the temptation to add new sockets to the existing circuits. All of this could add up to the possibility of dangerous overloading, not to mention the added trip hazards from trailing wires.

This would likely be compounded by not having RCD protection on circuits, and re-wireable fuses (which will let higher fault currents to flow and for longer before blowing).

Often older circuits did not have the earthing integrity (sometimes the earth being run as a separate wire for sockets, and often no earth at all in the lighting circuits).

If it was old enough you may even find rubber insulated cables on the lighting circuit - this will almost certainly have perished by now and can pose a major fire risk as the insulation will simple crumble off the wires if they ever get moved.

That do for starters?

[Sneezy]

John Rumm wrote in news:ouNZb.9116$Y% [e-mail]:

The measurement being the thickness of the copper.

Well the wiring all looks fine - flat grey modern cable. Slightly thinner for the lighting than for the sockets. The main problem was the consumer unit, which has now being replaced with a modern one with RCD. The earthing is a problem. I know at my old address there was earth wire connecting the hot and cold water pipes - nothing like that here. The only earth cable I've spotted is a tatty paint covered thing going from the consumer unit to the cold water pipe. I'd agree that what it looks like the "rewire" of the property consisted of replacing the old wiring with new rather than starting from scratch and properly designing the circuits and so on. The whole feel of the place smacks of unprofessional - the TV co-ax has a lump of wood hung from it (part of an old window frame methinks) and it's only the cold water pipe that it rests on that stops it from tearing all the cable clips out of the ceiling. Then there's the main pipe coming from the gas meter - bent with a lump hammer with the looks of it (seriously). Same with the main cold water pipe. Maybe I have high standards :)

Lighting seems fine. The hall pendant socket broke yesterday when I tried fitting a new bulb (!) so I guess I'll be able to assess the wiring quality when I replace the fitting.

Yes - very informative.

[Harry Bloomfield]

Sneezy wrote on Saturday (21/02/2004) :

Quite simply because radial circuits impose severe limitations on the number of sockets you can have in your home. The modern idea is to have sockets close to everywhere you might need to use one and keep the flex to appliances as short as is practicable. Short flexes and much safer than long ones where you might trip over them or they might become damaged. An adequate number of outlets also ensures you will not need to use multiple double adaptors. Without counting, I would guess we have around 60 or 70 socket outlets around my home. So many individually wired on radial circuits would just be impractical.

Your own suggestion that you do have so few, plus that they are wired on radial circuits tends to indicate that you should be looking at getting the whole lot rewired and to modern standards. My guess would be that nothing has been done to your installation since perhaps the

1950's or even earlier. Are the cable plastic or rubber (black)? Rubber cabling should have been replaced long since.

[Bob Eager]

Doesn't come across well in ASCII, but 2.5mm cable here is actually 2.5 square millimetres per conductor - not 2.5mm diameter.

[Owain]

"Sneezy" wrote | If I understand correctly, a ring main is a ring of wire on which | sockets (and spurs) are strung? Wire comes from the fuse board via | all the sockets and returns to the fuse board? My question is, | "why are they used?".

The ring main (ring final circuit) was developed in the aftermath of WWII when there was (a) a massive housebuilding programme (b) a shortage of copper (c) an increase in the number of small electrical appliances in use. The former method of radial circuits, with usually one 15A socket for the electric fire and a couple of 5A sockets for the iron and the wireless, was inefficient in use of cable etc.

The 30/32A ring main / 13A fused plug combination relies on diversity - although *any* socket *can* be fully loaded to 13A it is extremely unlikely that *all* will be heavily loaded simultaneously. For this reason, rings are unsuitable for permanent water or space heating. Simple calculation will show that *any two* sockets can be loaded to 13A and still leave 4A or 6A for small appliances. The fused plugs mean that small appliances with thin flexes can be safely used on a circuit fused at 30A.

One reason for the ring's design is that it was possible to take a pre-war house with two 15A sockets on radials and convert them into a ring circuit using the existing cables in situ.

Owain

[Sneezy]

"Bob Eager" wrote in news:176uZD2KcidF-pn2- [e-mail]:

That would be too simple. So A=pi*r^2 rearranged gives sqrt(A/pi) so 2.5 mm cable has a diameter of 0.89 mm - but my maths ain't that great. "Per conductor" as in "per wire in the cable"? That means that the cable I'm looking at right now (lighting cable supposedly), which has a diameter of

1mm, is actually 0.78 mm cable, which you can't buy so I'm confused. I can see why people use thick cable :)

[Sneezy]

"Owain" wrote in news: [e-mail]:

Yeah - hadn't thought of that. Just bung a wire in the socket and take it back to the consumer unit and hey presto - one ring main. I could almost do it myself ;)

I'm starting to think that who ever changed the wiring was capable of only that. A qualified eletrician wouldn't update the wiring but not take the opportunity to convert radial to ring, install a decent consumer unit, and ensure safe earthing. That said, the electrician that changed the consumer unit knew about the dodgy socket in the cellar but just left it because he wasn't paid to do anything other than change the unit. I would have made it safe at the very least - ethical and professional. I'm daft though :)

[Lurch]

It's not confusing once you know. I think the cable you have there will be 1mm^2, I doubt .22mm is easy to measure with a ruler. If you were to dig out a pair of vernier calipers though... Your theory is spot on, just the practical aspects needs brushing up on. ..

SJW A.C.S. Ltd.

[Sneezy]

[e-mail] (Lurch) wrote in news: [e-mail]:

I did this the other day too Managed to somehow calculate one week in a month :( It's the old age. My figures are all out because I'm forgetting to half D and double r. If it were 1mm^2 then it would measure

1.12 across which is roughly what I measure it to be, so 1mm^2 it is :) I guess experience tells you what cable you need without having to mess around with paper and calculator :)

[chris French]

In message , Sneezy writes

Cable is referred to by the above mentioned 'cross sectional area' you don't have to worry about what the actual diameter is.

Generally, in domestic situations, 1mm^2 (or sometimes 1.5mm^2) is used for lighting , 2.5mm^2 is used for ring mains and some radial circuits, thicker stuff is usuallly used for stuff like cookers, showers etc.

[usenet]

You can have as many sockets as you like on a 2.5sq mm radial circuit. The only difference in IEE recommendations for the two is that the ring circuit can serve up to 100 sq metres and the radial only 50 sq metres.

[usenet]

[Bob Eager]

The limitations are practical. You either have cables like hawsers, or lots of radials and a massive consumer unit.

[Owain]

Chris Green wrote | You can have as many sockets as you like on a 2.5sq mm radial | circuit. The only difference in IEE recommendations for the | two is that the ring circuit can serve up to 100 sq metres | and the radial only 50 sq metres.

And a 2.5mm radial is fused at 20A, so you can't max out 2 x 13A sockets and still have a bit left over.

Owain

[usenet]

And a 2.5mm ring circuit is fused at 32A, so you can't max out 3 x 13A sockets and still have a bit left over.

I.e. - so what?

[usenet]

Two radials will supply more power (more easily in my opinion) than a single ring circuit.

Ring circuits often do make sense in kitchens and utility rooms, radials make a great deal of sense elsewhere, e.g. a separate radial to my study to supply all the computer equipment there is a much more practical solution than a ring.

[Christian McArdle]

Basically, you only get a single fan heater on a 2.5mm radial, so when your CH blows up, you'll have more difficulty heating your house without tripping something.

Also, 20A would be pretty pathetic for a modern kitchen.

Christian.

[Lurch]

When radials were common electrical appliances weren't, most households had a lamp or two and not much else. Modern houses are rammed full of high rated appliances, you'd have to have a lot of radials to be able to have any redundancy. ..

SJW A.C.S. Ltd.

[Tony Bryer]

YMMV but when I was young (pre-c/h days) the main appliances were electric fires. Now houses are rammed full of appliances that use hardly any electricity: TV's, computers, VCR's, clock radios etc etc. Almost the only appliance in my home that uses serious power is my washer drier