I read an item in an old book here about a short-lived 5-wire DC system (Yes, five-wire!) which was installed in part of London for lighting in the 1880s.
Each house was connected to just two wires and ran with 100V lamps. The article doesn't mention which wire (if any) was grounded, but I would guess the middle one of the five. Even so, I wonder how many people got taken by surprise by one side of their 100V supplies being at 200V above ground.
Paul, For the most part, you are probably talking about the Edison generator I expect. No problem, this is where the brou-ha-ha began over grounding, they weren't. Remember the code was implemented by the Insurance Underwriters in those days, they rarely, if ever, insured lives, only buildings. We did not want those burning down, we had to pay for them. You can still see the same basic system in AC if you check out the Scott or "T" connection. The only place I've ever seen one is in coal mines. It is also the true "2 phase" system with each being 90 deg opposed instead of 120. A machine that can run on DC (such as most battery operated mining equipment) will also run just fine on this, with the help of a rectifier. Real pain to wire, and if you aren't familiar with it, Lord help you on troubleshooting.
Yes, it's certainly an interesting system. We had plenty of regular 3-wire DC Edison systems installed here, and a few of those kept going in the older parts of some towns well into the 1950s. I think a few of the very early ones were 120/240V (or thereabouts), but they were soon converted to 200/400 to 250/500V. I wouldn't be sure whether the insurance angle would have been the same over here in England at that time, though.
I picked up this snippet of information from a booklet published by the Science Museum in London about 30 years ago. Some time in the next few days I'll dig it out again and see if I can post some more details.
Oops, it looks as though I goofed a little -- Sorry! I was working from memory, and it's several months ago I read the book. Anyway, the 5-wire wasn't right back to the generating station but just within each building, and it was in Vienna, not London.
I like my humble pie served nice and warm please.....
Anyway, here's the appropriate section, from the book "R.E.B. Crompton, Pioneer Electrical Engineer," HMSO 1969:
Crompton spent much of the years 1885 to 1889 in Vienna lighting the Opera House, theatres and public buildings. The Ring Theatre, previously lit by gas, was destroyed by fire in 1883 with great loss of life. Emperor Franz Joseph decided that, for greater safety, electric lighting should be introduced. The Imperial and Continental Gas Company, who retained the contract for lighting the theatres, engaged Crompton to design and supervise the work and to manufacture some of the equipment.
A single central generating station supplied all the buildings, which were up to one mile away - a far more widespread system than any previously attempted anywhere in the world.
The highest voltage filament lamps then available required 100 volts. To obtain the advantages of high-voltage distribution (lower current and therefore cheaper cables) he devised the 'five-wire system' of supply with batteries at each load point (figure 20). The generating station operated at about 440 volts d.c. and charged a Crompton-Howell battery of 200 cells at each theatre or other consumer. The theatre lighting was divided between four circuits each supplied at 100 volts from one quarter of the battery. In the generating station six Willans 150 horsepower steam engines were each directly coupled to a Crompton generator. The generating capacity was over 700 kilowatts, and for special effects at the Opera 1000 kilowatts could be utilised, with the batteries discharging at their maximum rate.
The Opera House was the first large theatre to be lighted electrically. Bracket lamps were put on the fronts of the balconies and boxes, which was impossible with gas lighting because of the rising fumes and hot air. On the stage Crompton introduced coloured lights, separately controlled by resistance dimmers in which resistance coils were short-circuited by being lowered into a vessel of mercury. Several operas and ballets were put on to test the scenic possibilities, and Viennese society flocked to see what could be done with the 'electric gas.'
* Fig. 20 shows a 2-w supply to each bldg. to four series-connected 100V batteries, and a 5-w distribution from batteries to lights.
George was kind enough to give me some references to the 5 wire DC system. It's kind of an odd idea - but not too much in the "Whacko" realm
I'll compile some information, then draw up and post Schematics for this one.
P.S. I need to get back into the "Television / Telecommunications" discussion from the thread in "Non-US Systems" area. Found the papers I have which list the Frequencies of Telephone stuff [such as DTMF, dial tones, etc.].
Monty Python was on for a few days, and in some of the sketches, the Phone was ringing endlessly. Had the "Ring-Ring, Ring-Ring" Cadence you mentioned! Guess what the first thing I thought of when that phone rang??? You guessed it! My Friends got a good laugh out of that!
Scott " 35 " Thompson Just Say NO To Green Eggs And Ham!
I'm always interested in seeing alternative and obsolete systems, as they can show the historical development quite well. They sometimes explain why things are still done a certain way today. There used to be some overhead distribution systems which looked like 5-wire in some districts here. They were actually just a standard 4-wire Wye with the fifth wire used to switch pole-mounted contactors for street lights. On some old poles it's still possible to see the fifth insulator bracket in place, although the cable and insulators themselves have been removed. I haven't seen one of these systems since the 1980s, and they were rare by then, but there might still be one or two in use somewhere. If you look at old photos of many British towns, the "town centre" area (downtown) was often festooned with cables. Apart from domestic/commercial power and telephone, many were for the trams (what you would call a street car or trolley) or their successor, the trolley-bus. The latter were electrically powered buses running on normal tires for greater maneuverability, and thus needed two pick-up arms and twin overhead lines. All of that is gone, and over the years there has been a gradual move toward underground power & phone lines, much to the pleasure of many who obviously don't share our enthusiasm for looking at electrical systems. (Strange people! ) Drive through a typical British town today, and you'll certainly see less overhead linework than in the average U.S. town. *
P.S. The double-ring is certainly distinctive, although when simulated in movies or on TV the timing isn't always accurate.
[This message has been edited by pauluk (edited 11-25-2001).]
Your fig. 2B is the closest to the old Vienna system. Just assume each of the four battery banks is 100V and that they are located at the theatre or other building. The incoming 400V supply is then just 2-wire connected to the outermost pos. and neg. lines.
There's no indication as to any grounding; as George said, at that time there probably wasn't any.