But before that,, when elastictrickery was invented you had a coal fire that heated the whole house, or the family all sat round the fire in a sociable sort of fashion. When electric fires were brought in the problem was highlighted and, eventually, ring mains were devised. ..
SJW A.C.S. Ltd.
"Tony Bryer" wrote | Lurch wrote: | > 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. | YMMV but when I was young (pre-c/h days) the main appliances were | electric fires.
Which would have been on its own 15A plug. One per room. Probably next to the fireplace. Hopefully not with an unfused adapter down to 5A for the wireless.
| 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
Kettle, deep fryer, dishwasher, george forman grill, microwave, electric raclette, ...
Rings were designed to allow one or two (more subject to diversity) heaters, hence the floor limit, together with lots of little appliances, but with the flexibility to use any appliance in any socket.
The heating-appliance-hungry modern kitchen is contrary to the idea.
Owain
The consumer unit in my parents' American house (ring mains apparently being unknown) is about a square yard...
Just reading an American DIY book about house wiring. Amazing. They have these things called wirenuts, which are exactly what you might think, things you screw onto the ends of twisted-together wires to lock them together.
And why is it that all the light switches and mains sockets (sorry, receptacles) are a sort of off-white colour, even new ones in the stores. Real white seems to be a rarity.
They come in useful for sealing the end of tubes of silicone. I used to have a box full of ones pulled out of rewires. ..
SJW A.C.S. Ltd.
[...]
Oh I dunno. Under the On Site Guide (appendix 8, table 8A p151) you can have as many sockets as you like on a radial, so long as you restrict the amount of floor area they serve. In theory, a medium-sized semi (my parents' house) at about 90sqm could be served by just one ring circuit, but these days you would usually fit at least two, or often three, perhaps split between upstairs, downstairs and kitchen. In that case each ring circuit serves less than half of the 90sqm, and so you *could* wire it as a radial instead, and install just as many sockets using no more fuseways.
OSG p151:
"A ring or radial circuit, with spurs if any, feeds permanently connected equipment and an unlimited number of socket-outlets and fused connection units...
...Diversity... has already been taken into account in Table 8A and no further diversity should be applied
Table 8A [edited]:
Type Overcurrent device use PVC cable max. floor area
Ring 30 or 32A 2.5mmsq 100sqm Radial 30 or 32A 4.0mmsq 75sqm Radial 20A 2.5mmsq 50sqm"
If you wire it in 4mmsq wire with a 32A MCB then you have a circuit which is capable of supplying exactly the same amount of power as a 32A ring, though 4mmsq cable is rather more difficult to squash into the backboxes and slightly more expensive to buy (Screwfix don't even list the stuff in their catalogue!).
If you wire it in 2.5mmsq you have less overall power, but I would suggest that unless you have a very power hungry family, 20A is perfectly sufficient upstairs, and probably downstairs too, if the kitchen is separate.
This defence of radials should not, of course, be taken to mean that any existing circuits are fine - you should take the state and age of the wiring into account in deciding whether to rewire. All I'm saying is that you shouldn't discount installing a new radial when you are thinking about rewiring.
Hwyl!
M.
"Sneezy" wrote | > Kettle, deep fryer, dishwasher, george forman grill, microwave, | > electric raclette, ...
popcorn popper, cuddly toy ...
| Seems the problem is rich folk then. I can't afford to redecorate | on a yearly basis, so no fryer. Dishwasher? That's me. I have a | fridge-freezer, ancient rusting microwave, washer, cooker and | that's it. No modern appliances. CH is for softies - what's | wrong with a blanket huh?
Tends to lose its insulation value when you trip over the end on the way to the privy.
| No colour TV - black and white portable does me fine. £100+ pa | is a scandle for what's on. My "luxury" is my PC and even that | uses less than 1Kw. You're all too pampered :)
Eeh, when I were a lad we even 'ad glass in t'windows. Talk about soft living.
Owain
"Jim Hatfield" wrote | Huge wrote: | Just reading an American DIY book about house wiring. Amazing. | They have these things called wirenuts, which are exactly | what you might think, things you screw onto the ends of | twisted-together wires to lock them together.
I have some much-loved ceramic Scruits(tm) rescued from a rewired house which I find invaluable for a variety of low-voltage uses.
| And why is it that all the light switches and mains sockets | (sorry, receptacles) are a sort of off-white colour, even | new ones in the stores.
It hides the scorch marks from all those wirenuts overheating.
Owain
Conveyor belt. How many times do people miss that one?
PoP
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Snip ring final circuits.
The real reason for its allowance is probably from one of the Technical Committees who had a long lunch, one of their members could make 2.5mm T+E cheaply, and make a good profit on it, so he persuaded the others to go along with it. There is speculation on why we have the 5 seconds disconnection rule for distribution circuits - far too long, and pretty unsafe if you drill through it, and the usual answer is that there were so many fuses out there, British manufacturing couldnt make a Breaker to meet the 0.4 second rule, so 5 seconds was standardied, hence the power companies could continue to use their 100A fuses.
I know someone who is sitting on the Tech. Comm. re-writing Guidance Note 3 (Inspection and Testing), and they say it is comical some of the things that come up, there is little reasoning behind some of the articles, yet "it has always been done that way, so why change it?"
As for the RFC, there was a large consultation about circuits a couple of years ago, (it is all in a file on the IET site, though I cannot find it now), with a long presentation why RFCs should be removed for the
2011 Amendment, this gave the pros and (mainly) cons for them, with recommendations that they be removed from the standard circuit definitions, and only used for certain applications. The pro voice was heard after dinner, and the vote taken that things should stay as they are. When reading the minutes, it is pretty clear that there is a good case for removing them, but, cable makers sell more cable for rings, so they have a bigger voice.I've listened to a number of people who know the various writers of the Tech. Documents, and there are very few good remarks about them, the typical one being "out of touch" or "not open to reason".
Alan.
Well, there's a very tiny bit of truth, corrupted by gross inaccuracies which could be a case of chinese whispers - gradual corruption each time the story was retold.
Firstly, a "Ring Main" applies to electricity distribution in the street to premises, and at a higher level, distribution between areas. It is commonly incorrectly applied to the 30A/32A final ring circuit in the home, which I assume is what was meant here.
The earlier wiring schemes used radial circuits with a 15A socket on each radial circuit, back to a fuse in the fuse box. Most rooms only had one 15A socket, so this was not too onerous. Sometimes a 5A socket was also provided for light loads. As electrical appliances grow in popularity, the idea of only one socket in each room rapidly became unviable, but also the idea of routing loads of 15A circuits back to the fusebox was also not viable. It was recognised that you probably didn't need more than 15A in a room (the room would get uncomfortably hot if you did), but you might want to draw that load from anywhere in the room, and indeed split it over multiple outlets. Thus was born the (now obvious) idea of multiple socket outlets.
This was considered for some years pre-WWII, but implementation came at the end of WWII when there was a shortage of copper. This influenced the design which became the final ring circuit we know today. The idea was to provide unlimited socket outlets, but to recognise that only a certain amount of power was required over any floor area, and not the maximum which each socket could provide all at once. The design also allowed easy conversion from
15A radials to 30A ring circuit by reusing the same wire (although that probably wasn't as common as had been envisaged). The design included a move to a single socket type to handle everything, from the horibble mixture of earlier 15A, 5A, 2A, 2- and 3-pin sockets to make life much simpler.I think it's a design which has lasted and worked very well. There have been very few later corrections required (upping the earth conductor size is the only one I can think of, apart from a few safety improvements to the 13A plug). As such, the opportunity to chuck out what we had before and start again was a real benfit, and it was probably done at the last moment it could have been before proliferation would have made any such change impossible.
Well, for a start, 2.5mm cable arrived rather later - about 20 years later. The originals used 7/029 cable.
And why would you want a 5 kW heater for localised - ie portable - use? 3 kW is enough for most rooms.
15 amp was the largest common socket size before rings.Was this written by some US wag? The home of electrical fires cause by their mickey mouse wiring? Wire nuts indeed - rightly banned here years ago.
You can post stuff like that you will upset the people that don't understand the cons, those people have a name.. electricians.
Its well enough known. Re other reasons why it was implemented, maybe there were a few people that thought 5kW heaters and other such things were a good reason to go with rings, but that wasnt the main reason. Bear in mind that electric heating beyond a background level in the
40s was prohibitively expensive, so its not an idea that would have had much support. 5kW 240v =3D 21A21A requires 2.5sqmm 30A requires 4sqmm
there was also earthing, thermal overcurrent breakers and various other protections. Fuses totally dominated breakers for reasons of cost & safety.
yes
A 5kW plug fuse is no more reliable in tripping than a 5kW fixed wiring fuse. In fact the CU fuse is quicker at tripping, because of other loads also on the circuit, and again because of less likelihood of abuse.
Rings are much safer and use less copper in the great majority of domestic property layouts.
That would make every connection in the circuit safety critical. A single bad conection then risks fire or shock, soemthing that doesnt occur with rings. It also reduces the utility of the system, since each circuit is less tolerant of large combination loads. Finally it offers zero safety advantage. 30A fusing protects the ring circuit itself fine, and plug fuses protect the appliances and their leads
Its more the sort stuff that is too much talked about ring circuits by those that dont understand them. There's nothing glamorous about them, but they have saved many lives due to their excellent tolerance of poor connections, which are a fairly common occurrence.
NT
As do Circuit Breakers. The point was, in the late 40's, British manufacturing did not have the technology to make breakers at a competitive price, so the fuse stayed as the main protection into the
80's, and is still the main protection for distribution boards.A synopsis of it is here:
It gives the usual arguments. I was talking last week to an attendee of that event, and he said the anti-rfc argument was far stronger, and agreed by most people as sensible (they should not be used, apart from specific applications) but dinner (or a break according to the timetable) intervened, and it was agreed for no action, apart from the ones at the bottom of the report.
The full report is available somewhere, though google has failed me.
Alan
But in the 1940s-50s most rooms were unheated anyway and 'central heating' would probably have been run to about 16-17 degC rather than the 21 degC + typical today. Most people sat in the lounge and listened to the wireless whilst wearing sweaters, not spread themselves all over the house in t-shirts.
Referring to Ministry of Works Technical Notes No. 4 (price sixpence net):
In the average small house or flat not exceeding 1,000 sq ft in floor area it is reasonable to assume that the maximum demand for uses other than for fixed lighting and cooking will not be greater than 7 kW (30 amp) however many sockets are provided.
The table for locations/numbers of sockets shows:
living rooms - 3 (fire, lamp, radio & tv) bedrooms - 2 (fire, lamp) kitchen - 3 (fridge, washing machine, iron)
A typical 3 bed semi would therefore have 1 ring circuit and 15 socket outlets.
I think I'm up to 24 in my lounge alone.
Owain
Our first house, bought in 1964, was the result of a division in 1946. There were 4 power points; one in each bedroom and one in the kitchen. There was also a lighting point in the living room. Nedless to say, my first job was rewiring.
There was no such thing as 2.5mm T&E in those days. The first 20-30 years of domestic ring mains were wired with good old stranded tin plated 7/029 T&E which is near 2.9mm T&E in this modern rubbish!
Yes, I knew that, the argument is still the same, in that manufacturers had more say than legislators/Standards Techs, so their views held sway.
Alan.
Was it really necessary to increase the earth conductor size? It was only needed in some cases where rewireable fuses were used. It may have been more economical to have outlawed fusewire, requiring cartridge fuses and MCBs to be used.
With Ed17 requirements for RCDs even fusewire would be adequate for the earth wire. 8^|.
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