I'm late replying to this, I know... On Thu, 19 Oct 2006 08:57:58 +0100, slippyr4 wrote: > > I read the history of British electrical systems once and as I recall, = the loop system was implemented to save metal. Since any plug is actually f= ed = from both sides of the loop the wire only needs to be rated for ~1/2 the to= tal current. Ours is a single ended daisy chain, so the wire must be rated = for the full current. But we only have a fuse/breaker at the service panel,= so the sum current of the entire string can't exceed the rated current. In = practice handheld appliances seem to rated less than 1500W (hair dryers, el= ectric fry pans, tea kettles etc) > > > = > It's true. We call it a "ring final" circuit. = Ah, so you're a professional sparky then! :-) You used the proper term, w= hereas everyone else calls it a "ring main"... > It's other benefit is > that the CPC (the ground) is connected from two places, so is half as > likely to be broken. It also reduces the effect of any high resistance, such as loosely-clamped = wire in a socket, because of the sharing of the load in both directions. A = radial ("daisy-chain") circuit relies on every connection being a good one,= and the importance of this increases as you approach the feed end. > Every socket in the UK has an earth (ground) pin (at least every > socket made since the '20s). Every plug has a fuse in it, although in > some situations a faulty appliance may trip the circuit's breaker > rather than blow the fuse (due to the fuse blow characteristics) And if you have *really* gone for it, the service fuse too! :-) = > Your handheld appliances are all rated below 1500W because of the way > your houses are wired. Over here, it's common for appliances to pull > much more - because they can. Kettles are often 2-2.5KW, = Actually I was looking at a few in a shop recently, and nowadays most of th= em seem to be rated at 3kW (at 240V of course, since at 230V that would = be over 13A). > we have > electric heaters at 2KW, etc. Of course, yours still work - but ours > boil the water / heat the house quicker. Again, a three-bar electric fire would be 3Kw, and we had one when I was a = kid (early 1960's), and I remember the fishy smell the plug would give = off it you ran all three bars all evening, as my father tended to do, espec= ially in the Winter of '63... = > > > If you're doing something industrial that needs more than 3kW you can= either hard-wire, or use industrial plugs which handle 16 or 32A, but = you'd > > > never normally see those in a house or garage, even a garage-workshop. > > > > = > That's the same here. The maximum any one socket is designed to deliver i= s 13A. That was here - you were quoting me! :-) = > > Most commonly circuits are 14ga wire and rated for 15 amps. Some specif= ic circuits are rated for 20 amps and use 12ga wire > = > We measure cable here in square millimetres. But, according the IEE > Wiring Regulations (the UK electrical code), a cable doesn't have a > rating *per se*. Rather the designer of the installation must > calculate a suitable size of cable based on it's expected load, length > (for meeting voltage drop requirements), the way it's installed (ie, > embedded in a wall, clipped to a wall) for thermal derating, and > whether it's grouped with other cables, as well as the earth fault > loop impedance (which must be low enough to ensure that the circuit > breakers will break within the required time when a dead short > occurs). Right, but you must admit that *most* 32A ring finals are wired in 2.5mm=B2= Twin & Earth. There are time where the calculations would mean you'd = have to go to 4mm=B2, but that would be exceptional. (That's square millim= etres, in case the little 2 doesn't travel!) > > Hard wire is reasonably common for lots of things, but we also have a m= yriad of other plugs for high current devices to about 50A. Electric clothe= s = dryers at 220V 30A, electric ranges at 220V 50A. Higher than that is common= enough in industrial settings (I've seen 480V 500A three phase = connectors) > = > cookers and showers are the only *common* domestic hard wired appliances = here. And Immersion Heaters and the supply for gas boilers - for the latter not b= ecause of the current requirement, which is only a couple of amps, but = because it shouldn't be unplugged. > > Another interesting quirk is the voltage. It's common to talk about 110= /220, but some people say 120/240. The plug next to me actually measures = 117V. Some other places I've lived were closer to 110V and I worked in one = place that measured 124V. And even though the USA is "standardized" on = 60 Hz, I believe there are a couple small islands up near Maine that use 50= Hz and last I knew there was a generator plant at Niagara Falls that = produces 25Hz for a few industrial customers. > = > Europe used to have a nominal 220V, and the UK used to have a nominal > 240V. But these nominal voltages were defined with a tolerance. > = > Recently, the nominal voltage in europe has been changed, to 230V. > But, sneakily, the tolerances changed with it - in the UK it's 230V > +6%/-10% . I believe (but not certain) that continental europe is 230V > -6%/+10%. Other way round, I think - I believe it's currently 230 +10/-6% in the UK, = giving a top of the range of 253V, which where I am they occasionally excee= d! = According to my UPS its maximum in the past 5 minutes was 249.6V, and that'= s not unusual, especially at this time of night. Now that's not a very = accurate meter, but it's not far out and it's certainly around 245V now. = > However, most houses still see about 240V at the wall. The tolerances > neatly shift the burden of compatibility onto appliance manufacturers. I believe they are going to widen it further, to 230V +/- 10% for the whole= of Europe, giving a range of 207 to 253V. = > > As they say, The best thing about standards is there are so many to cho= ose from. > > > I think that's one of the advantages of the fact that the UK is so > small - we just have one standard. Nowadays, yes, but within my lifetime there were still DC mains supplies in= a few places in the UK! As soon as everyone gets onto one standard, they come up with another one..= . when I was a lad the wires were red/black/green and the normal = thickness for ring finals was 7/.029 (seven strands of 29-thou wire), then = it changed to red/black/green&yellow, 2.5mm=B2 single strand, now the wire'= s = the same but the colours are brown/blue/green&yellow. Ah well, it all make= s for an interesting life! :-) Cheers, Howard Winter St.Albans, England -- = http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist