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UK diy (uk.d-i-y) For the discussion of all topics related to diy (do-it-yourself) in the UK. All levels of experience and proficency are welcome to join in to ask questions or offer solutions. |
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American electrics
This is a US CU:
http://electrical-contractor.net/jt/mainrng4.jpg and this is the install: This house was built in 1940, and wired with an early form of Romex...Cloth wrapper, no ground wire. Apart from the water bond, there is no grounding. All receptacles are two-prong. The only bath recep is part of the light over the mirror. The main room, with almost fifty feet of perimeter, has exactly one receptacle. The only kitchen receptacle shares a single-gang box with a switch for the exhaust fan. It sure is a different world over there! The whole thread is he http://electrical-contractor.net/ubb...ML/000135.html NT |
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In message ,
Owain wrote: wrote: This is a US CU: http://electrical-contractor.net/jt/mainrng4.jpg and this is the install: This house was built in 1940, and wired with an early form of Romex...Cloth wrapper, no ground wire. Apart from the water bond, there is no grounding. All receptacles are two-prong. The only bath recep is part of the light over the mirror. The main room, with almost fifty feet of perimeter, has exactly one receptacle. The only kitchen receptacle shares a single-gang box with a switch for the exhaust fan. Hmmm. I don't think British wiring would have been much better - especially with it being war-time. Of course, our wiring has improved considerably since then; we've even banned wire-nuts. Theirs hasn't, and they haven't. The comment I liked was the one which said something along the lines of "The hospital where I worked had these things, installed in 1933. They were replaced when the wards were remodelled in 1995". Those bods don't seem to like their "thermomagnetic breakers". In what way do their breakers differ from our modern MCBs? Hwyl! M. -- Martin Angove: http://www.tridwr.demon.co.uk/ Two free issues: http://www.livtech.co.uk/ Living With Technology .... Answers on a postcard please to 10 Downing Street, London SW1. |
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Martin Angove wrote:
In message , Owain wrote: Hmmm. I don't think British wiring would have been much better - especially with it being war-time. Of course, our wiring has improved considerably since then; we've even banned wire-nuts. Theirs hasn't, and they haven't. The comment I liked was the one which said something along the lines of "The hospital where I worked had these things, installed in 1933. They were replaced when the wards were remodelled in 1995". Exactly, nail on head. 1930s wiring is common place over there _today_ in 2005. Having no earth anywhere on your presmises is considered normal, numerous old installs are like that. I've only once ever seen anything that ancient over here. Those bods don't seem to like their "thermomagnetic breakers". In what way do their breakers differ from our modern MCBs? I dont know, but I know enough about merican lectrics to know their kit is generally of way lower quality than here. For example the standard insulator on bulb holders is a piece of card, and the standard socket cable connector is a flat spring, not a screw connection. So I wouldnt be surprised if their mcbs were slow, unreliable, or overheated. NT |
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In article ,
Martin Angove writes: The comment I liked was the one which said something along the lines of "The hospital where I worked had these things, installed in 1933. They were replaced when the wards were remodelled in 1995". Those bods don't seem to like their "thermomagnetic breakers". In what way do their breakers differ from our modern MCBs? My impression from reading US NG's is that their breakers are not unknown for burning out, falling to bits, drifting trip values, etc. which I've never come across with ours. If you pick the things up in Home Depot and look at them, they just don't feel anything like the same quality as ours either. The funny thing is some of them are same manufacturers as the EU ones, but obviously built to different standards (and possibly price -- I don't recall how that compared with ours). Many of their older breakers are thermal only, and don't have the fast fault current response ours do. I don't know if all their current breakers have the magnetic trip component. If you get to go to the US, a stroll through the electrical section of Home Depot is really quite frightening. However, you'll find many more things stocked which you won't find stocked in B&Q and would be special order only from even a UK electrical wholesaler. -- Andrew Gabriel |
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Those bods don't seem to like their "thermomagnetic breakers". In what
way do their breakers differ from our modern MCBs? They have thermal trip only. They cost about 1.3p to make in some sweatshop and are as reliable as a clingfilm condom. The US electrical system is simply unsafe compared to the rest of the world. It largely comes down to: Lower voltage. 110V is much more dangerous than 230V. This isn't obvious to the non-technical, but the US went with "common sense" (aka thick people's prejudices) rather than sound scientific analysis. The basic issue is that very few people die of electrocution, whilst loads of people die from electrical fires. The electrical fires largely stem from high currents. If you halve the voltage, you double the current. The high voltage has other safety benefits, too. For example, during an earth fault, the higher voltage leads to much higher current flow. An overcurrent safety device is, thus, much more effective, leading to much more rapid disconnect of the circuit. Some numbers. Take a hypothetical circuit rated for a bit over 3kW. In the US, this would be 110V, 30A. If the breaker requires 5x current to trip immediately, this requires an earth impedence of 0.73 ohm right back to the substation. Of course, most US circuit breakers are thermal anyway, so trip is never immediate. With less than about 0.73 ohm, it will take much longer to trip (or perhaps it never trips, if the earth loop impedence is too high). A slightly higher energy circuit in the UK would be 230V, 15A. The required earth impedence is now 3.8 ohms. This is extremely easy to achieve, unlike the 0.73 ohm, which might even be impossible. Another effect of the low voltage is that "respect" for electricity is lower. The lower voltage leads to lower quality insulation on fittings, cheaper parts and a blase attitude of users to electrocution. The result of this is that the US actually has a higher electrocution death rate per capita than the UK, despite the lower voltage! When you compare the incidence of electrical fires, the differences become much more scary. Other differences in the US: 1. Low quality cables that have arcing failure modes, leading to fires. 2. Use of wirenuts. 3. Combination of neutral to earth (i.e. effectively TN-C earthing) leading to electrocution in the event of polarisation swap, or some open circuit conditions. TN-C earthing in banned in Europe, except in special (non-domestic) cases. 4. Provision of socket outlets in bathrooms, so users dry their hair in the bath. Christian. |
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In article ,
"Christian McArdle" writes: Lower voltage. 110V is much more dangerous than 230V. This isn't obvious to the non-technical, but the US went with "common sense" (aka thick people's prejudices) rather than sound scientific analysis. The basic issue is that Actually, the choice of mains voltage on either side of the pond was not decided on safety grounds. The safety issues were largely unknown at the time. very few people die of electrocution, whilst loads of people die from electrical fires. The electrical fires largely stem from high currents. If you halve the voltage, you double the current. and quadruple the overheating effect. Other differences in the US: 1. Low quality cables that have arcing failure modes, leading to fires. 2. Use of wirenuts. 3. Combination of neutral to earth (i.e. effectively TN-C earthing) leading to electrocution in the event of polarisation swap, or some open circuit conditions. TN-C earthing in banned in Europe, except in special (non-domestic) cases. 4. Provision of socket outlets in bathrooms, so users dry their hair in the bath. You missed: 5. the crap quality of their socket outlets, responsible for many fires. 6. building regulations which hinder people modernising their wiring, so extremely old wiring still in use is very much more common. Oh hang on, scratch that one, we just introduced the same regulations here. -- Andrew Gabriel |
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You missed:
5. the crap quality of their socket outlets, responsible for many fires. Actually I included that under the low voltage section, as it is the low voltage that makes them think they can get away with it, although I suspect it is just a cheap as possible, don't care attitude, really. Christian. |
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On Wed, 1 Jun 2005 10:31:18 +0100, "Christian McArdle"
wrote: The electrical fires largely stem from high currents. If you halve the voltage, you double the current. ....For a given power rating... :-) (Just to avoid confusing beginners!) -- Frank Erskine |
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Andrew Gabriel wrote:
6. building regulations which hinder people modernising their wiring, so extremely old wiring still in use is very much more common. Oh hang on, scratch that one, we just introduced the same regulations here. Even with Prat P we dont rent out apartments and blocks all wired a la 1930s in 2005... its either legal over there or not enforced. I suspect legal, given the litigius society and wide spread of 30s electrics, waaaaaaaay past their scrap by date. What people often dont stop to think is that a typical 1930s install today would even fail a /1930s/ safety inspection, due to deterioration and additions leading to overloading. NT |
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wrote in message oups.com... Andrew Gabriel wrote: 6. building regulations which hinder people modernising their wiring, so extremely old wiring still in use is very much more common. Oh hang on, scratch that one, we just introduced the same regulations here. Even with Prat P we dont rent out apartments and blocks all wired a la 1930s in 2005... its either legal over there or not enforced. I suspect legal, No it is not legal. On a large Middle East US site I was at, it was all conduit and 1930s electrics. In plants rooms not a bit of mineral insulated cable to be seen (the norm in Europe). I asked why mineral insulated cable had not been used, and none of them had heard of it. One knowledgeable man said mineral insulated is used in the US, but infrequently because of cost. This I found strange as installing metal conduit is not cheap. The merits of conduit were given to me and how cheap is just to pull though extra wires or to replace. I asked them how often do you replace wires? Slapping pyro around the walls is not that expensive in comparison. The US appears habitual in many aspects, although they did abandon fuses to a large extent. given the litigius society and wide spread of 30s electrics, waaaaaaaay past their scrap by date. What people often dont stop to think is that a typical 1930s install today would even fail a /1930s/ safety inspection, due to deterioration and additions leading to overloading. _________________________________________ Usenet Zone Free Binaries Usenet Server More than 120,000 groups Unlimited download http://www.usenetzone.com to open account |
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#14
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In article ,
Jim Hatfield wrote: I have an American "domestic electrical diy handbook" and it's fascinating. I'd never seen a wirenut before I read that. They were fairly common in the UK many years ago. I found some in my house used with lead cable. So I'd guess pre WW2. -- *He who laughs last, thinks slowest. Dave Plowman London SW To e-mail, change noise into sound. |
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Christian McArdle wrote:
4. Provision of socket outlets in bathrooms, so users dry their hair in the bath. Theres a famous picture of an American extension lead made by someone who remarkably survived. He put 2 sockets into a cut open shampoo bottle and taped it all up. The idea was it would float. Yep, float, in his pool. Appaerntly it was so he could watch tv while in the pool. NT |
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In article ,
Huge wrote: I replaced the garbage disposal in my mother's house (in Pennsylvania) a few months ago. Good things; Huge individual circuit breaker panel easily available in the kitchen, so no grovelling under the stairs and having to switch off an entire ring to isolate the garbage disposal. You wouldn't in the UK either. It would have been either plugged into the ring, or isolated by a double pole FCU, etc. -- *A 'jiffy' is an actual unit of time for 1/100th of a second. Dave Plowman London SW To e-mail, change noise into sound. |
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Garbage disposal!
Useless devices IMHO; today we too compost. Although the heap sometimes freezes during the winter. Heap also produces worms for trout fishing. Worms flourish on discarded banana skins, potato peelings, other kitchen discards of the non-meat variety along with last year's raked leaves. Recall semi amusing event: About 48 years ago someone gave us a brand new under sink mounting 'Garbage Disposal' unit. It had about a third HP 115 volt 60 Hertz motor! Installed it in the 35 by 8 foot house trailer we then lived in. Worked fine until the sewer line blocked. Not knowing line was blocked, or perhaps in an attempt to blow the obstruction down the pipe towards the septic tank, I forget which, I switched it on, fully loaded with water and with the tap running! Result was a jet of water and other 'unmentionable stuff' straight up out of the vent pipe in roof of the trailer. A neighbour said "It WAS quite sight". So was the clean up! Ever try cleaning sprayed 'cr*p' off the aluminium siding, roof and windows of a trailer (caravan)? .................................................. . snipped .................................... I replaced the garbage disposal in my mother's house (in Pennsylvania) a few months ago. Good things; Huge individual circuit breaker panel easily available in the kitchen, so no grovelling under the stairs and having to switch off an entire ring to isolate the garbage disposal. You wouldn't in the UK either. It would have been either plugged into the ring, or isolated by a double pole FCU, etc. Good point. We've never had one, on account of having a compost heap. -- "The road to Paradise is through Intercourse." [email me at huge [at] huge [dot] org [dot] uk] |
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In article ,
Derek * writes: On Fri, 03 Jun 2005 20:19:20 +0100, "Dave Plowman (News)" wrote: In article , Jim Hatfield wrote: I have an American "domestic electrical diy handbook" and it's fascinating. I'd never seen a wirenut before I read that. They were fairly common in the UK many years ago. I found some in my house used with lead cable. So I'd guess pre WW2. I used them when I spent a couple of weeks working for an electrician when I was in the 6th form, that would place it in 1963. They were called "Scruits" (TM) Yes, that's a tradename. "Dogs ********" was a nickname, which came about due to the way a pair of them would dangle below a cable knot. I have a number of old books on wiring (stangely, I find the history of it interesting). The most recent one with any reference to this type of connector is about 1935, and that's only in a picture -- I suspect thet were probably rather obsolete even by then. Ceramic chocolate block connectors were well established by then, together with a one terminal single ended chocolate block connector which looks like a screwit but cylindrical rather than tapered. Oh, and today's circular junction boxes with the slotted terminals just start appearing (with screwed lids at that time). I'm fairly sure I've recently seen them inside multiple ceiling light fittings (3-lights etc) and ceiling fans. Those are single-ended insulated crimps, which look similar but are _far_ more reliable... -- Andrew Gabriel |
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Andrew Gabriel wrote:
They were called "Scruits" (TM) ... I have a number of old books on wiring (stangely, I find the history of it interesting). The most recent one with any reference to this type of connector is about 1935, and that's only in a picture -- I suspect thet were probably rather obsolete even by then. I had an electrical wiring book in the mid 1980s which recommended them. Can't remember which one though. Owain |
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In article ,
Huge wrote: You wouldn't in the UK either. It would have been either plugged into the ring, or isolated by a double pole FCU, etc. Good point. We've never had one, on account of having a compost heap. I've never seen the point either. Unless in a 45th floor apartment with no rubbish disposal facilities. -- *If only you'd use your powers for good instead of evil. Dave Plowman London SW To e-mail, change noise into sound. |
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Dave Plowman (News) wrote:
I've never seen the point either. Unless in a 45th floor apartment with no rubbish disposal facilities. The Saniflo is not the only waste disposal device invented by a Frenchman. google Garchey - I think the first site is the Barbican Estate Underground page, will tell you all you didn't want to know. Owain |
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In article ,
Owain writes: Andrew Gabriel wrote: They were called "Scruits" (TM) ... I have a number of old books on wiring (stangely, I find the history of it interesting). The most recent one with any reference to this type of connector is about 1935, and that's only in a picture -- I suspect thet were probably rather obsolete even by then. I had an electrical wiring book in the mid 1980s which recommended them. Can't remember which one though. Well, there are loads of books which recommend them in 2005 too, to Americans... -- Andrew Gabriel |
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Andrew Gabriel wrote:
They were called "Scruits" (TM) ... I have a number of old books on wiring (stangely, I find the history of it interesting). The most recent one with any reference to this type of connector is about 1935, and that's only in a picture -- I suspect thet were probably rather obsolete even by then. I had an electrical wiring book in the mid 1980s which recommended them. Can't remember which one though. Well, there are loads of books which recommend them in 2005 too, to Americans... Yebbut this was a British book, and referred specifically to Scruits for doing loop ins in lighting circuits. I have some genuine glazed porcelain scruits and find them preferable to any plastic imitators. Owain |
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In article ,
Huge wrote: I've never seen the point either. Unless in a 45th floor apartment with no rubbish disposal facilities. My Mum lives in a tiny town house with no (private) garden. In the summer, the temperatures stay 30 deg C for days on end. A garbage disposal is essential. You're cruel to your mum. I hope she cuts you off without a penny. With your vast house you must have room for a granny flat. ;-) -- *I don't have a solution, but I admire your problem. * Dave Plowman London SW To e-mail, change noise into sound. |
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Jim Michaels wrote:
Hi, I will assume that your post is not bait and is serious You make some good points, but there are a few I'll pick up on: On Wed, 1 Jun 2005 10:31:18 +0100, "Christian McArdle" wrote: The US electrical system is simply unsafe compared to the rest of the world. true, at least compared to UK. Maybe not the world, US seems the model of good practice compared to African practices, and that of many other countries. Current, of course). Edison's first great central station, supplying power for three thousand lamps, was erected at Holborn Viaduct, London, in 1882. Does anyone know the voltage that was used? In any case the U.S. Voltage is due to historical factors. I am sure the British voltage was not selected much more recently. but this doesnt change the fact that 110 is inherently more dangerous than 240. With 240v we treat it with respect, with 110v people relax since it wont electrocute them, and hurts waaay less if they get bit. They worry less about cord grips etc. The result is fires, which are the prime killer, not electrocution. The basic issue is that very few people die of electrocution, whilst loads of people die from electrical fires. The electrical fires largely stem from high currents. If you halve the voltage, you double the current. NOT TRUE. You are making multiple invalid assumptions. 1. That U.S. wiring has the same number of circuits for the same load. still cant figure out what you mean there. For a given load you do have higher i with lower v, and each load is on 1 circuit as far as i can see. 2. That U.S. circuits are not designed for their load. I dont think that was the assumption: the problem is simply theyre designed to have a higher incidence of faults. The practice of push-in connection on mains sockets is something considered unthinkable here, for good reason. Use of single insulated mains flex has been illegal for decades, etc etc. 3. That electrical fires occur in properly designed circuits simply due to higher currents. we know its due to many factors. 4. You claim lower voltage equals higher current, then you say... The high voltage has other safety benefits, too. For example, during an earth fault, the higher voltage leads to much higher current flow. An overcurrent safety device is, thus, much more effective, leading to much more rapid disconnect of the circuit. It seems you contradict yourself. no contradiction there that i see, just an example of how higher v gives a safety benefit. If the breaker requires 5x current to trip immediately, this requires an earth impedence of 0.73 ohm right back to the substation. Note: Our circuit breakers magnetic trip are similar to your type D should give less nuisance trips, ours sometimes trip on bulb failures. The required earth impedence is now 3.8 ohms. This is extremely easy to achieve, unlike the 0.73 ohm, which might even be impossible. Again, in the U.S. a 3kW circuit would be 240V 15amp and the same benefits would apply. In US IIUC it would be called 240v, but in fact be 120-0-120, so the voltage from earth is 120 ac, not 240. In which case the fault clearance benefit of genuinely 240v would sometimes apply and sometimes not. Some faults that smoulder at 120 can arc over and trip at 240. Another effect of the low voltage is that "respect" for electricity is lower. The lower voltage leads to lower quality insulation on fittings, cheaper parts and a blase attitude of users to electrocution. The result of this is that the US actually has a higher electrocution death rate per capita than the UK, despite the lower voltage! When you compare the incidence of electrical fires, the differences become much more scary. Please quote sources for statistics. 2. Use of wirenuts. Why Not? they were banned here long ago because they cause connection failures and fires. They dont provide anywhere near the clamping pressures of our screw connections. 3. Combination of neutral to earth (i.e. effectively TN-C earthing) leading to electrocution in the event of polarisation swap, or some open circuit conditions. snip In the past it was permitted for the neutral to be used to ground the frames of ranges and dryers. This came about as Interim Amendment No. 53 put into effect on July 10, 1942. This was to allow the neutral to ground the frames by means of a bonding jumper from the frame to the neutral. The reason for the amendment was to save raw materials like rubber and copper for the effort of WWII. that much is fair enough, but... This special amendment however was not removed from the NEC until the 1996 code cycle. remarkable. At least not something normally permitted here. But we do have a permited 2 conductor wiring system, I forget the details, ISTR maybe it uses MICC? I'm not sure, but I'm pretty positive there still is one here, but it is not AFAIK permitted in domestic premises. Don't ever accuse us of not making sacrifices ;) I think the general complaint was that America makes more sacrifices, unnecessary human ones unfortunately. FWIW we had 110 dc here as well in the 50s, but this has universally disappeared now. NT |
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#27
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Jim Michaels wrote: In any case the U.S. Voltage is due to historical factors. I am sure the British voltage was not selected much more recently. Both the US and British voltages are a result of history. The British started with 100V IIRC, (100V was picked (by Edison)as it is a nice round number!) then moved up to 220V DC as it was cheaper to distribute power at the higher voltage. Parts of Camden Town in London were only converted from this in 1958. When the power supply world moved on, in the UK, AC was introduced and AIUI the available transformer stampings were optimal at 50Hz. The US came in with AC a bit later IIRC, and by then the laminations would sustain 60Hz, reducing the transformer size( & cost) and centre tapping the 230V allowed the use of the old distribution circuits and products without upgrading. If we were starting again today the world would probably settle for 230V @ 400 Hz, giving smaller ( &cheap) transformers without significantly increased losses. The US consumer has a product penalty as a result of using 230V, in that 2KW per 120V appliance is probably a realistic limit for the house wiring used, hence electric toasters and kettles are a pale shadow of the European ones. Also DIY tools, just do not have the "grunt" achieved by 230V. Dishwashers also are frequently hot fill. However 240V centre tapped is a lot safer than 0 - 240V IMO. US wiring is, I believe, produced to a higher temperature performance specification than Europe. Certainly this is true for internal wiring in consumer products. Having experienced US wirenuts, I can confirm that they are a fire on the way to a happening with solid cables and would never be accepted in the UK. US wiring in conduit is much safer from an accidental shorting viewpoint than UK wiring just buried in walls and if conduit wires are used, is much easier to modify. I believe the UK has very acceptable standards for wiring, but would probably benefit from using a 120-0-120V system on the grounds of safety and has gone over the top on equipotential bonding. On a basic level, who cares if the fault current is not sky high as long as the trip works! Just a few comments Regards Capitol |
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"Capitol" wrote in message ... In any case the U.S. Voltage is due to historical factors. I am sure the British voltage was not selected much more recently. Both the US and British voltages are a result of history. The British started with 100V IIRC, (100V was picked (by Edison)as it is a nice round number!) then moved up to 220V DC as it was cheaper to distribute power at the higher voltage. Parts of Camden Town in London were only converted from this in 1958. When the power supply world moved on, in the UK, AC was introduced and AIUI the available transformer stampings were optimal at 50Hz. The US came in with AC a bit later IIRC, I don't know what frequency (or voltage) he used but Tesla's company distributed AC mains in the US before it reached Europe. |
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Mike wrote:
"Capitol" wrote in The US came in with AC a bit later IIRC, I don't know what frequency (or voltage) he used but Tesla's company distributed AC mains in the US before it reached Europe. Edison decided dc was superior, and many a battle was fought over ac vs dc. It didnt take long to realise Edison had not made a good judgement on this point, but he continued his marketing battle by publically electrocuting animals on ac current for entertainment. NT |
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On Sat, 18 Jun 2005 22:58:54 +0100,it is alleged that "Mike"
spake thusly in uk.d-i-y: [snip] I don't know what frequency (or voltage) he used but Tesla's company distributed AC mains in the US before it reached Europe. From http://en.wikipedia.org/wiki/Alternating_current , so it may be inaccurate but sounds reasonable: "It is generally accepted that Nikola Tesla chose 60 hertz as the lowest frequency that would not cause street lighting to flicker visibly. The origin of the 50 hertz frequency used in other parts of the world is open to debate but seems likely to be a rounding off of 60hz to the 1 2 5 10 structure popular with metric standards." From my own knowledge I am fairly certain that a German company was responsible for the usage of 50 Hz in Europe, it may have been Siemens, but my memory is fallible :-) In any case, in a region like Europe, having a well established AC system of one frequency in the area would tend to encourage the usage of that frequency elsewhere to facilitate crossover of equipment and appliances, thus leading to savings in various things I slept through in economics class;-) -- The government's view of the economy could be summed up in a few short phrases: If it moves, tax it. If it keeps moving, regulate it. And if it stops moving, subsidize it. - Ronald Reagan |
#31
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In article ,
Capitol writes: Both the US and British voltages are a result of history. The British started with 100V IIRC, (100V was picked (by Edison)as it is a nice round number!) then moved up to 220V DC as it was cheaper to distribute power at the higher voltage. Parts of Camden Town in London were only Most of the early generation was at 100V. It suited arc lamps and the filament lamps of the time. Trouble was it wouldn't reach further than a few city blocks. I don't think there's any real concensus why many of the UK power stations switched to 200V and the US didn't, but one reason which does seem to have more credibility than others is as follows. Very early on, many London boroughs banned overhead cables (and those bans are still in effect today). This forced the cabling to be underground in much of London, but it was mostly on poles in the US at the time. Now what do you do when you have a local supply infrastructure that no longer meets the local demand? In the US, it was easy, you just string thicker cables on the poles. In London, with the cables all being underground, this wasn't possible without doing a complete new installation. So the way round the problem was to double the voltage, and we got lots of 200V supplies. Over the years, the voltage has continued to creep up in small increments. By the late 1950's, most of the UK mains final supply voltage was in the 200-250VAC range depending what town you lived in, and it was all changed to 240VAC in the early 1960's. Some areas with lots of cinemas also retained DC supplies for some commercial customers -- much of central London had a 220VDC supply until the late 1970's. converted from this in 1958. When the power supply world moved on, in the UK, AC was introduced and AIUI the available transformer stampings were optimal at 50Hz. The US came in with AC a bit later IIRC, and by then the laminations would sustain 60Hz, reducing the transformer size( & cost) and centre tapping the 230V allowed the use of the old distribution circuits and products without upgrading. If we were starting again today the world would probably settle for 230V @ 400 Hz, giving smaller ( &cheap) transformers without significantly increased losses. 400Hz severely reduces the maximum area of a synchronisation zone, which makes carrying power any distance very much more expensive. Many of the 50Hz zones are close to their size limit now, so I don't think anyone would think of distributing at any higher frequency in Europe. It would be OK on a small isolated island. 400Hz isn't suitable for industrial motors either. Actually, supplies to large commercial customers at 16 2/3rds Hz and 25Hz used to be quite common as they much prefer a lower frequency for large motors. Transformer size is really only an issue on planes and boats, which often do use 400Hz. -- Andrew Gabriel |
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On a basic level, who cares if the fault current is not sky high as
long as the trip works! Well, because it clears the fault more reliably and leads to fewer fires and deaths? Christian. |
#33
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Christian McArdle wrote: Well, because it clears the fault more reliably and leads to fewer fires and deaths? Where is the evidence for this? Most fires are due to poor connections, they won't necessarily trip the breaker until much too late! I noticed some comments earlier in the thread on the phasing problems of 400Hz. There are no problems if the main distribution system is HVDC. This is why major power links have been HVDC for many years AIUI. The 50Hz local distribution system is purely historic and well entrenched but the transformer sizes could be substantially reduced with 400HZ. In the US, local transformers on a pole appear to be the norm in a lot of areas. These would certainly be lighter at 400Hz. The 400 Hz suggestion comes from discussions with US engineers many years ago on which way would you go today if you could start again. I certainly like it. I haven't kept up to date with the power side of electrical distribution for a few decades, but sub 50Hz supplies were normally achieved locally by six and twelve phase transformers with interphase reactors, and not generator sourced. Sub 50Hz harmonics can be a major headache for distribution transformers AIUI so local generation seems essential. Regards Capitol |
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In article ,
Capitol wrote: I noticed some comments earlier in the thread on the phasing problems of 400Hz. There are no problems if the main distribution system is HVDC. This is why major power links have been HVDC for many years AIUI. The 50Hz local distribution system is purely historic and well entrenched but the transformer sizes could be substantially reduced with 400HZ. One problem is it's slap in the middle of the most sensitive part of the human audio band. Expect the average transformer to make the most annoying noise. -- *Work like you don't need the money. Love like you've never been hurt. Dave Plowman London SW To e-mail, change noise into sound. |
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On Tue, 21 Jun 2005 01:23:11 +0100,it is alleged that "Dave Plowman
(News)" spake thusly in uk.d-i-y: In article , Capitol wrote: I noticed some comments earlier in the thread on the phasing problems of 400Hz. There are no problems if the main distribution system is HVDC. This is why major power links have been HVDC for many years AIUI. The 50Hz local distribution system is purely historic and well entrenched but the transformer sizes could be substantially reduced with 400HZ. One problem is it's slap in the middle of the most sensitive part of the human audio band. Expect the average transformer to make the most annoying noise. Good thought, ouch. 400 Hz is the NU tone frequency before BT started using silly announcements, I would _not_ want that in the substation next door. -- "The perfect computer has been developed. You just feed in your problems and they never come out again." - Al Goodman. |
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In article ,
Capitol writes: I noticed some comments earlier in the thread on the phasing problems of 400Hz. There are no problems if the main distribution system is HVDC. Except for the cost of the converters at each end of the line, which is astronomic compared with cost of transformers. This is why major power links have been HVDC for many years AIUI. The HVDC is used to cross synchronisation areas. It is also advantageous in cables where the DC stresses the insulation less than AC. But the cost of the end station plant and any line switches means it's used only when absolutely essential. Generally it's much cheaper to make sychronisation zones as big as possible. Great Britain is all one zone. I haven't seen a recent map of Europe, but prior to the fall of the Berlin wall, continental Europe was 2 zones, the West controlled by Switzerland, and the Eastern European countries controlled from Moscow (although the USSR itself was multiple zones -- too big for one zone). The East and West zones weren't linked -- cost of the converters made it non-viable. GB and the West were/are linked across the English Channel on DC links, through which we buy the output of the French nuclear power plats they build along their north coast, due to the politics involved building them 25 miles further north in the UK. 50Hz local distribution system is purely historic and well entrenched but the transformer sizes could be substantially reduced with 400HZ. In I don't think anyone cares about transformer size anything like to the extent you seem to. the US, local transformers on a pole appear to be the norm in a lot of areas. Well 120V doesn't go very far before the regulation has gone to pot. These would certainly be lighter at 400Hz. The 400 Hz suggestion comes from discussions with US engineers many years ago on which way would you go today if you could start again. I certainly like it. I I think it's a non-starter. -- Andrew Gabriel |
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Andrew Gabriel wrote:
In article , Capitol writes: 50Hz local distribution system is purely historic and well entrenched but the transformer sizes could be substantially reduced with 400HZ. I don't think anyone cares about transformer size anything like to the extent you seem to. Cost. It may not be much per item, but add all those small cost savings up and it comes to 1 with a long string of 0s on the end. Savings on all domestic transformer operated gear, from wall warts to stereos to microwaves. Savings on all inductor fluorescent lights. Savingsd on reservoir capacitors everywhere. Savings on motor caps and pf correction caps. Etc. If we were starting from scratch now, we could save a nice little pile with 400Hz - or if the sync zone would not be big enough to cover UK, maybe less, but high than 50. Question: in this day of rf comms anad accurate time standards, why can we not use one central standard to sync gens all across the country, or anywhere as large as is wanted. It may have not been that way in 1900, but accurate time standards are fairly trivial now. the US, local transformers on a pole appear to be the norm in a lot of areas. Well 120V doesn't go very far before the regulation has gone to pot. These would certainly be lighter at 400Hz. The 400 Hz suggestion comes from discussions with US engineers many years ago on which way would you go today if you could start again. I certainly like it. I I think it's a non-starter. It is now, because of all the 50 and 60Hz kit. Theres too much of it that wont be replaced any decade soon. And its not really practical to make everything 50/400 compatible for the next half a century before switchover. The noise issue would not (need to) be a problem. Appliances would have a noise rating and probably legal requirements, just as they have various other requirements and ratings. NT |
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Andrew Gabriel wrote:
writes: Capitol writes: Wall warts are purchased in bulk for figures like 30p each, so they must already cost less than this to manufacture, including the transformer. Maybe you could knock 5p off the price of a wall wart? 400Hz means a wart small enough to fit into a high top mains plug in many cases. It means a far smaller TF. So lets say we cut from 30p to 20p each at the factory gates, or =A32 to =A31.33 on the retail shelf. Now, how many warts have you bought in total? Lets take a vague guess at 10. Times 60 million people in UK gives us: factory gates savings of =A360 million and consumer savings of =A3400 million. And thats just for warts, which are definitely not the biggest saving. microwaves. Savings on all inductor fluorescent lights. Savingsd on These are all going electronic anyway. not microwaves. We might save =A35-10 retail per nuke. Say =A35, and say a history of 5 nukes owned per person. 5 x 60 mill x =A35 =3D =A31.5 billion Get the picture? Question: in this day of rf comms anad accurate time standards, why can we not use one central standard to sync gens all across the country, or anywhere as large as is wanted. It may have not been that way in 1900, but accurate time standards are fairly trivial now. It's not a time standard problem, it's a transmission line problem. The National Grid is a large transmission line, and different parts of it will be at slightly different phase angles due to transmission delays. Now that might not be an insurmountable problem if it was just a long 1-dimensional line, but it's a complex 2-dimensional mesh, and the problem rapidly becomes unsolvable as the mesh size grows or the frequency increases. I don't know what the wave propagation velocity is on the National Grid, but best case it's the speed of light, so you have a 1/4 wavelength phase shift in around 1000 miles. At 400Hz, you shrink the max length of a synch zone to just 1/8th size, which is 1/64th of the area, so you need 64 times as many synchronisation zones and a collosal number of expensive conversion stations to feed power between unsynch'ed zones. OK, I'll rephrase the question: why can all gens not be synced by a common time standard instead of by the neighbouring mains waveform? I don't think that's the only issue. Another one which just occurs to me would be skin depth effect on large high current conductors; not insurmountable, but you'd have to change the conductors to multiple strands or flat tapes at 400Hz for smaller conductor sizes than is required at 50Hz, which would make cables and terminations more expensive. skin effect at 400Hz?? NT |
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wrote in message oups.com... Andrew Gabriel wrote: writes: Capitol writes: OK, I'll rephrase the question: why can all gens not be synced by a common time standard instead of by the neighbouring mains waveform? Laws of physics - there are stupendous forces involved in trying to drag an alternator out of synchronism once its locked in. I'd have to dig my old student days books out of the loft to find the calcs but one of the examples we studied on a 250MVA unit slipping by a factor of 0.1 astounded the whole of our group. The synch restoring torque was massive |
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