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| (832016) | |
Fourth Rails and Safety |
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Posted by Subterranean Railway on Fri Sep 11 11:05:08 2009 I've always wondered about the safety of fourth rail systems, as they would exponentially increase the chances of serious injury or death were one to fall into the roadbed. Does anyone have any statistics on the matter? I've never been able to find any.(I posted this as a response to a previous thread, but received no replies.) |
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Re: Fourth Rails and Safety |
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Posted by MGL on Fri Sep 11 19:30:45 2009, in response to Fourth Rails and Safety, posted by Subterranean Railway on Fri Sep 11 11:05:08 2009. There are two running rails, a power rail, what exactly is the purpose of this fourth rail?Michael |
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Re: Fourth Rails and Safety |
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Posted by chuchubob on Fri Sep 11 19:36:38 2009, in response to Re: Fourth Rails and Safety, posted by MGL on Fri Sep 11 19:30:45 2009. There are two running rails, a power rail, what exactly is the purpose of this fourth rail?Two power rails, like trackless trolleys have two power wires; the running rails are not used as an electrical ground. |
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iPhone 6 (4.7 Inch) Premium PU Leather Wallet Case - Red w/ Floral Interior - by Notch-It |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Fri Sep 11 19:41:33 2009, in response to Re: Fourth Rails and Safety, posted by MGL on Fri Sep 11 19:30:45 2009. Protection of the tunnels from electrolysis. I don't recall the exact voltages, it's somewhere around 700 volts and one rail does negative 350 and the other one does positive 350 with the rails at earth ground as normal. Prevents corrosion of the iron tunnel structures ... |
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Re: Fourth Rails and Safety |
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Posted by Union Turnpike on Fri Sep 11 19:45:07 2009, in response to Re: Fourth Rails and Safety, posted by MGL on Fri Sep 11 19:30:45 2009. The London Underground uses this. The third rail is +420 VDC and the center return rail is -210 VDC. Not sure what might happen if someone got on the tracks at an Underground station. |
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Re: Fourth Rails and Safety |
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Posted by MGL on Fri Sep 11 20:03:20 2009, in response to Re: Fourth Rails and Safety, posted by chuchubob on Fri Sep 11 19:36:38 2009. It's an energized return to ground rail?Michael |
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Re: Fourth Rails and Safety |
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Posted by MGL on Fri Sep 11 20:04:51 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Fri Sep 11 19:41:33 2009. "Protection of the tunnels from electrolysis"We wouldn't want the tunnels hair falling out, would we? Michael |
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Re: Fourth Rails and Safety |
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Posted by MGL on Fri Sep 11 20:06:02 2009, in response to Re: Fourth Rails and Safety, posted by Union Turnpike on Fri Sep 11 19:45:07 2009. There is such a thing as negative voltage?Michael |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Fri Sep 11 20:07:26 2009, in response to Re: Fourth Rails and Safety, posted by MGL on Fri Sep 11 20:04:51 2009. Heh. Actually, electrolysis in DC transit systems has always been a problem known as "stray voltage" ... you guys have those problems in the form of corrosion of steel everywhere. Back in the "trolley" days, it was known to corrode gas pipes and water pipes and still does unless your rail returns and grounding are *perfect* ...And as to the hair falling out, long long time ago, the IND was lined with mink. NOW look at it! Heh. |
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Re: Fourth Rails and Safety |
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Posted by MGL on Fri Sep 11 20:14:25 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Fri Sep 11 20:07:26 2009. That's strange, I thought I saw some fur fly today.In order for the ground to be perfect, it needs to be energized? or am I over simplifying this thing. Michael |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Fri Sep 11 20:26:34 2009, in response to Re: Fourth Rails and Safety, posted by MGL on Fri Sep 11 20:06:02 2009. Sure is ... and very common in most DC electronics. Rare for traction of course, but quite common in DC systems. And where the two polarities returned was called "common" and truly "ground."
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Fri Sep 11 20:28:53 2009, in response to Re: Fourth Rails and Safety, posted by MGL on Fri Sep 11 20:14:25 2009. Actually, ground should be NOT energized. It's the return path to the power source. If ground *is* energized to *any* amount, you end up with stray voltage through the ground itself and current will flow to pipes and other things that really *are* at ground potential. This causes electrolysis because of that leakage current.Fur, eh? Sure it wasn't a steel dust bloom? :) |
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Re: Fourth Rails and Safety |
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Posted by Union Turnpike on Fri Sep 11 20:45:13 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Fri Sep 11 20:26:34 2009. As the name implies, the center return rail returns the electricity. Looks like Lionel O Gauge track. |
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| (832230) | |
Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Fri Sep 11 20:58:26 2009, in response to Re: Fourth Rails and Safety, posted by Union Turnpike on Fri Sep 11 20:45:13 2009. I was never fond of O gauge because the tracks are *so* unprototypical. But the design *does* make it nice and easy to form a loop without insulators. |
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Re: Fourth Rails and Safety (PHOTOS) |
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Posted by ChicagoPCCLCars on Fri Sep 11 21:15:34 2009, in response to Fourth Rails and Safety, posted by Subterranean Railway on Fri Sep 11 11:05:08 2009. I too was fascinated by the fourth rail when I visted London's Underground last year. Here are some of the pics from that trip. The station pic shows a trough beneath the rails. Is this perhaps a safety place should a person fall from the platform?    David Harrison |
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Re: Fourth Rails and Safety |
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Posted by Jackson park B Train on Fri Sep 11 21:33:01 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Fri Sep 11 20:28:53 2009. disagree. article sometime back reccomending a small DC current on AC building ground so as not to have the driven rod 'give away' metal. Also note, per the NECode all metallic piping in a building must be 'bonded' thus the gas, hot water, cold water electrically connected. However, this is building side of the meters which are electrically isolated so no juice should flow to the utility system gas pipes. |
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| (832238) | |
Re: Fourth Rails and Safety |
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Posted by Wado MP73 on Fri Sep 11 21:35:53 2009, in response to Fourth Rails and Safety, posted by Subterranean Railway on Fri Sep 11 11:05:08 2009. While I don't have any statistics, one of my London Underground books says it's more dangerous than three rail in case a person falls on the tracks.It was actually an American (Yerkes) who decided to use four rail electrification on the later tube lines and eventually that system was adopted on sub-surface lines and earlier tube lines (except the Waterloo & City which wasn't part of LU) as well. The Waterloo and City got four railed much later in the nineties when the ownership was transferred and rolling stock common with the Central line started to be used. The Northern City line was once converted to LU style four rail but was converted to Southern type three rail when it was transferred to the BR in the mid-seventies. |
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Re: Fourth Rails and Safety (PHOTOS) |
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Posted by JohnL on Fri Sep 11 21:37:15 2009, in response to Re: Fourth Rails and Safety (PHOTOS), posted by ChicagoPCCLCars on Fri Sep 11 21:15:34 2009. The pits in underground stations are indeed for those unlucky enough to fall before the train. They are known colloquially as “suicide pits”. |
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| (832243) | |
Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Fri Sep 11 21:48:50 2009, in response to Re: Fourth Rails and Safety, posted by Jackson park B Train on Fri Sep 11 21:33:01 2009. They're actually talking about galvanic protection, normally done with a sacrificial anode made of zinc or other metals which are sacrificed instead of the steel and piping. The "grounding and bonding" requirements are to ensure that no stray currents flow from pipes to ground or other metallic surfaces by tying them all together to ground so as to eliminate any potential stray current.AC power isn't so much of a problem at all since the polarity reverses 60 times a second. The real problem for galvanic corrosion is the result of DC flow only such as in electric railway systems and of course, subways. |
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| (832245) | |
Re: Fourth Rails and Safety |
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Posted by Bill West on Fri Sep 11 21:53:29 2009, in response to Re: Fourth Rails and Safety, posted by MGL on Fri Sep 11 19:30:45 2009. Boy is this getting off course....Michael, 1. electrolysis as a hair treatment is nothing to do with electrolysis as a corrosion mechanism. Lots of English words have multiple uses. 2a. the leads from a simple DC power supply are usually marked for their polarity ie positive and negative. This shows the direction of current flow. So if you measure from + to - a meter will show +600 volts but if you swap the meter leads the display will say -600 volts. That’s all that is meant by negative voltage. 2b. Selkirk’s sketch is for 3 wire supplies that are intended to provide 2 or 3 voltages to different loads at the same time. Many applications ground the center connection but it does not always have be, it depends on what the rest of the design is doing. 2c. Lionel track is 2 running rails and the “third” rail in the middle, there is only one voltage. It’s not grounded either. 2d. 4th rail traction systems do not use the running rails for power at all and they do not have to ground either of the two power carrying rails, although they could. What most do is put a ground somewhere near the center of the power supply. This may not be able to supply power the way Selkirk’s sketch does however. The ground may just be a sensing relay that spots insulation failures on the 2 power rails and the power rectifier is just connected to the 2 power rails. The reason for using the 4th rail is indeed likely to be historical corrosion concerns. 3. To answer your original question a. if the power supply is completely ungrounded, 4th rail would be safer as you would have to touch both power rails at once to get hurt. For other technical reasons this is not a good system to use, it introduces other safety hazards the most basic of which is that half your insulation can fail without anyone knowing about it. b. if the power supply is grounded on one side the system is the same as a 3rd rail and the 4th rail is a waste of time. c. if the power supply has either a power ground or a sensing ground near the center, 4th rail would be poorer because there are more places you can accidentally touch. Even a sensing relay would pass enough power to stop your heart. Whether the voltage you touch is 210 or 420 is not an issue either. But as you’ve found there doesn’t seem to be any data on 4th rail, possibly because it was not likely an original reason for choosing it and because the statistics would probably be too small to make an argument against the corrosion concerns. Sort of like asking would being hit in the head at 30mph by a metal cover over the coupler be safer than being hit directly by the coupler. Being on the roadbed is extremely risky no matter how you rate the individual hazards so I doubt if anyone cares about the extra power rail. Bill |
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Re: Fourth Rails and Safety |
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Posted by Broadway Lion on Fri Sep 11 22:20:44 2009, in response to Re: Fourth Rails and Safety, posted by MGL on Fri Sep 11 20:03:20 2009. Yes. The trains run on say 600vDC...The center rail has -200vdc and the outside rail carries +400vdc (or somew arrangement like that. The LION has not tested the actual potentials with his volt meter, your ZAP may vary. ROAR |
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Re: Fourth Rails and Safety |
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Posted by Jackson park B Train on Fri Sep 11 22:53:12 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Fri Sep 11 21:48:50 2009. occasionally we electricians see a nearly gone drivenrod. makes us scratch head. |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Fri Sep 11 22:57:17 2009, in response to Re: Fourth Rails and Safety, posted by Jackson park B Train on Fri Sep 11 22:53:12 2009. My favorites are the 3 footers driven into dry sand. Yeah, that helps. :( |
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| (832286) | |
Re: Fourth Rails and Safety |
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Posted by Jackson park B Train on Sat Sep 12 00:21:16 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Fri Sep 11 22:57:17 2009. yeah, there was a rumor out here about a company that cut the 8 fgooters in half. Can you guess my attitude? OTOH, in a couple cases where there is not much dirt over large rock, I have ended up driving several until they bent. In one case FOUR each about 4 1/2 in. |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Sat Sep 12 01:29:30 2009, in response to Re: Fourth Rails and Safety, posted by Jackson park B Train on Sat Sep 12 00:21:16 2009. Yeah, the NEC prefers one find another location and drive it 10 feet. When you're less than that, you need to mitigate the soil, add salt and find a means to keep it moist somehow. Bein a high power RF madman myself, there's one at every corner of the building and everything is strapped with 0000 copper. I no fuggaround. :) |
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| (832302) | |
Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Sat Sep 12 01:54:22 2009, in response to Re: Fourth Rails and Safety, posted by Bill West on Fri Sep 11 21:53:29 2009. Just wanted to make a point as an electrical engineer about (2b) back there. For the voltages to be a negative ~200 and a positive ~400, there has to be a common (ground) reference in order to split those voltages between the two power rails as such. And as electric railroads discovered much to their dismay in the early 20th century, that common traction power return path can either be through the rails themselves or through stray paths which is what caused all the concern about the electrolysis issues way back when ... just a thought. :) |
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Re: Fourth Rails and Safety |
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Posted by Jackson park B Train on Sat Sep 12 01:59:36 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Sat Sep 12 01:29:30 2009. obviously no copper savages eh? last rock job I managed to get 8 ft @ a 45 degree angle which the inspector okayed. |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Sat Sep 12 02:08:15 2009, in response to Re: Fourth Rails and Safety, posted by Jackson park B Train on Sat Sep 12 01:59:36 2009. The inspector shouldn't have signed off on it. It's about depth, not length. If you'd driven that in New York state, we'd be after you. especially if you were a cable or telephone company.But yeah, having built facilities that regularly got hit by lightning, our close location to a 465kV power yard and local lightning hits in the summer months here along with some sensitive electronics, I went nuts. I admit it ... but we've taken a few hits here since I've lived here and nothing smoked. Heh. |
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Re: Fourth Rails and Safety (PHOTOS) |
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Posted by MattW@15st_prospect_park on Sat Sep 12 02:37:47 2009, in response to Re: Fourth Rails and Safety (PHOTOS), posted by JohnL on Fri Sep 11 21:37:15 2009. FOund on the deep level lines to make is esaier to remove the dead. |
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| (832312) | |
Re: Fourth Rails and Safety |
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Posted by Subterranean Railway on Sat Sep 12 02:44:17 2009, in response to Re: Fourth Rails and Safety, posted by Bill West on Fri Sep 11 21:53:29 2009. The center rail does not merely exist as a current return path grounded in strategic places to alleviate electrolysis of neighboring infrastructure; it's actually energized at approximately -210 volts in conjunction with the ~420 volt side rail. A reference point is established by bridging the two current-carrying rails with a voltage divider tapped to ground.Sort of like asking would being hit in the head at 30mph by a metal cover over the coupler be safer than being hit directly by the coupler. WADR, this is a very poor analogy. Merely being on a traditionally-electrified system's roadbed is far from certain death. Being on the roadbed is extremely risky no matter how you rate the individual hazards so I doubt if anyone cares about the extra power rail. Countless people fall into roadbeds; I've witnessed a couple accidents firsthand (and I'm not an especially frequent mass transit rider). I've even helped a woman who was unable to climb back up to the platform by herself. Neither of these people would have been so fortunate in a LU-esque electrified system, as both ended up in the trough after their falls. Unless a person is disoriented, the principal danger of being in a traditionally-electrified system's roadbed is an oncoming train, which, while certainly considerable, is relatively easily avoided.1 It seems a far graver danger exists in the LU, where merely falling on the roadbed in the absence of trains can quite easily kill. 1: Except in stations where the third rail lies underneath the platform edge, in which falling on the third rail poses a real danger. |
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Re: Fourth Rails and Safety (PHOTOS) |
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Posted by Subterranean Railway on Sat Sep 12 02:45:46 2009, in response to Re: Fourth Rails and Safety (PHOTOS), posted by JohnL on Fri Sep 11 21:37:15 2009. Unless the pit were electrically isolated, I don't think I could wiggle into one of those without zapping myself. |
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Re: Fourth Rails and Safety |
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Posted by Subterranean Railway on Sat Sep 12 02:53:42 2009, in response to Re: Fourth Rails and Safety, posted by Wado MP73 on Fri Sep 11 21:35:53 2009. Interesting. I didn't know Yerkes influenced the system before his arrival in 1900. (IINM, the fourth rail was implemented in the 1890s.) |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Sat Sep 12 02:56:19 2009, in response to Re: Fourth Rails and Safety, posted by Subterranean Railway on Sat Sep 12 02:44:17 2009. Actually, if you end up in the trough AND do not make contact with either rail, then you do not complete the circuit and die. However, with the energized rail cutting the distance between running rails in half, your chances aren't quite as good. I suppose it's healthy to frighten people about the 600 volts under the cover boards off to the sides of the rails on third rail systems, but most rubber boots (as long as they have no pinholes or wetness) and even some ordinary SHOES (as long as they are thoroughly dry) offer sufficient insulation at 600 or 750 volts although touching or kicking is NOT recommended. :)I remember "track safety" when I was there, and in our official booties, they made us kick the third rail for kicks and scaring off the probies who were scared of electricity. But the LU system sure does enhance your chances of getting fried. No question of that. :( |
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Re: Fourth Rails and Safety (PHOTOS) |
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Posted by SelkirkTMO on Sat Sep 12 02:58:14 2009, in response to Re: Fourth Rails and Safety (PHOTOS), posted by Subterranean Railway on Sat Sep 12 02:45:46 2009. The LU is remarkably "moist" even if there aren't puddles down there. There's probably more than enough conductivity to ground on the surface of the concrete to do the nasty. Definitely to be avoided. |
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Re: Fourth Rails and Safety |
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Posted by Subterranean Railway on Sat Sep 12 03:05:57 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Sat Sep 12 02:56:19 2009. However, with the energized rail cutting the distance between running rails in half, your chances aren't quite as good . . . But the LU system sure does enhance your chances of getting fried. No question of that. :(Exactly my point. I'd still like to see stats, because the LU's electrification system just seems incredibly dangerous to me. I'd be willing to bet that 99% of 12-10s in the New York System occur completely without incident or report. Wonder what that figure is in the LU. :-/ but most rubber boots . . . and even some ordinary SHOES . . . offer sufficient insulation at 600 or 750 volts A friend of a friend who used to write in the tunnels said he's nicked the third rail a few times while wearing sneakers. While the permittivity of most substances (including air) is surprisingly high, it's not something I'd care to test. |
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Re: Fourth Rails and Safety |
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Posted by Bill West on Sat Sep 12 03:46:16 2009, in response to Re: Fourth Rails and Safety, posted by Bill West on Fri Sep 11 21:53:29 2009. Selkirk-as Subterranean points out the grounding can be at the center of a resistance divider. The electrolysis is avoided by not having the return grounded rather than by just making the grounded return through the rail better than through the neighboring structures. The “better ground path” is what the streetcar companies progressed to but in London the returning motor current just doesn’t touch the ground at all. Bad rail joints would not divert current into the earth because it does not lead back to the ends of the power supply. By the way Amtrak’s 132,000 volt transmission lines also do this (for fault protection reasons), the power transformers have a center tap grounded through a 330 ohm resistor. Subterranean -re your “The center rail does not merely exist as a current return path grounded in strategic places to alleviate electrolysis”, in 2d I only mentioned solid grounding as one possible way. Then I mentioned center tap or sensor grounding as being “what most do” so we are speaking of the same thing. -re being hit as poor analogy I was expressing my opinion that being exposed to only one live rail is not very much of an advantage over being exposed to two. This is in part because during this question the risk of being hit remains rather large. My view was based on the regular “12-9’s” here. Despite escape space people do seem to get killed on the road bed too often. In fact the reports speak in terms of being hit but rarely mention electrocution. Bill |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Sat Sep 12 04:00:42 2009, in response to Re: Fourth Rails and Safety, posted by Subterranean Railway on Sat Sep 12 03:05:57 2009. Heh. Yeah, better to kick tires. :) |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Sat Sep 12 04:14:27 2009, in response to Re: Fourth Rails and Safety, posted by Bill West on Sat Sep 12 03:46:16 2009. Understood ... but bear in mind I'm also no expert in electric railways, but as I've read the issues, the problem in many DC traction systems where electrolysis was an issue was that the rails provided insufficient current flow back to the powerhouse, and instead, the traction current found its way back to the dynamo by means of soil conductance. Little was known about stray voltage back in the early days which of course is why railroads use thermite bonds these days. :)As to Amtrak, and other AC-powered traction, electrolysis cannot be an issue because the current reverses at a regular rate. Any ions stripped from a metal are returned when the current reverses. Try electroplating metal with AC voltage across the soup. Nothing gets plated. Only under DC supplies does this issue rear its ugly head even though practical mitigation techniques DO exist, and WORK on DC electric railways. It was unknown back then how MUCH of an influence a few ohms of resistance can raise at high voltages and high currents such as streetcar lines and such. Nowadays, that stray current can be reduced to mere milliamps. In the OLD days, the leakage was substantial. And in poorly maintained modern railways, it still can occur from time to time due to negligence. That all said though, what I can't wrap my mind around is that if you have a DC circuit and you measure across the mains, or with a load in parallel on it, you get only ONE voltage reading. Only when you add a ground reference on a bipolar circuit, can you measure a minus 200 on one power supply rail (and yes, railroad rail too) and a positive 400 on the other. Therefore there HAS to be a ground reference which is an *active* part of the circuit, and in particular the power supply. I surmise that ONE rail on LU is grounded, and IS a return to the substation if not both rails, depending on how the signal plant is wired. Otherwise, the only means of determining the voltages is across the two power rails and the correct answer there would be ~600 volts of either polarity (depending on which rail the red meter lead goes to) but it would not be possible to measure a + and a - voltage with respect to common. Just me, science can be irritating at times, particularly if we're not looking at the same schematic. :) |
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Re: Fourth Rails and Safety |
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Posted by Wado MP73 on Sat Sep 12 04:30:49 2009, in response to Re: Fourth Rails and Safety, posted by Subterranean Railway on Sat Sep 12 02:53:42 2009. (IINM, the fourth rail was implemented in the 1890s.)Mid-1900s, and he was dead by then. He never saw any of his tube lines either. |
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Re: Fourth Rails and Safety |
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Posted by Subterranean Railway on Sat Sep 12 09:57:19 2009, in response to Re: Fourth Rails and Safety, posted by SelkirkTMO on Sat Sep 12 04:14:27 2009. Two bleed resistors of 220Ω and 110Ω (negative and positive, respectively) in the form of a voltage divider periodically earth BOTH rails.I'd write more, but I actually managed to dig up a patent for an "apparatus [for] monitoring an earth-leakage state of a power distribution system" for DC four-rail traction systems. IINM, this seeks to address the rather large voltage fluctuations in the LU's system. Great read, and answered most of my still-unanswered technical questions. |
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Re: Fourth Rails and Safety |
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Posted by Subterranean Railway on Sat Sep 12 10:15:54 2009, in response to Re: Fourth Rails and Safety, posted by Bill West on Sat Sep 12 03:46:16 2009. Then I mentioned center tap or sensor grounding as being “what most do” so we are speaking of the same thing.Great, glad we're on the same page. :-) My view was based on the regular “12-9’s” here. Despite escape space people do seem to get killed on the road bed too often. Indeed, as I mentioned, being 12-9'd is a considerable risk. But think of how many 12-10s occur without anyone's knowing. (As I said, I've seen two myself, and I don't even ride that frequently. How's that for an indicative sample size? ;-) ) It usually isn't especially hard to climb out of the roadbed or otherwise get out of the path of a train unless one falls while a train is imminent. In that case, stay in the trough! In fact the reports speak in terms of being hit but rarely mention electrocution. Reports where? In New York, 12-10s are generally only reported if they become 12-9s, which occurs in a tiny minority of cases. I was expressing my opinion that being exposed to only one live rail is not very much of an advantage over being exposed to two Considering the position of the second live rail, I'd say the additional hazard's considerable. It's between the two running rails, exactly where someone to fall would land. Unless the person managed to stay un-grounded (not likely), chances of escape are slim. (Personally, I think the LU's system helped gave rise to the popular misconception that ALL railroad tracks are live.) |
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Re: Fourth Rails and Safety (PHOTOS) |
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Posted by ChicagoPCCLCars on Sat Sep 12 11:15:32 2009, in response to Re: Fourth Rails and Safety (PHOTOS), posted by JohnL on Fri Sep 11 21:37:15 2009. Thanks JohnL. We have little small platforms at track level at the ends of old "L" stations here in Chicago. The extensions are called "fool catchers." Goes back to the days at the turn of the last century when riders riding overcrowed trains would cling inbetween cars and in rare cases hang onto the outside end gates.I also love the phrase "fall before the train." David Harrison |
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Re: Fourth Rails and Safety |
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Posted by SelkirkTMO on Sat Sep 12 13:35:02 2009, in response to Re: Fourth Rails and Safety, posted by Subterranean Railway on Sat Sep 12 09:57:19 2009. Wow ... that's some fairly high resistance for the application. :)Well ... that's an answer! |
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Re: Fourth Rails and Safety |
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Posted by Bill West on Sat Sep 12 15:59:02 2009, in response to Re: Fourth Rails and Safety, posted by Bill West on Sat Sep 12 03:46:16 2009. Selkirk-okay, I think you’re now reading this as a resistance ground. Low enough for a sensor to be able to detect insulation failure on either rail, low enough to resist the voltage division from drifting due to insulator leakage. But still enough to prevent either power rail from getting close to zero volts and becoming paralleled by the earth, followed by electrolysis. -Amtrak’s case was for fault protection reasons, electrolysis was not the issue. It was just to point out another case where a center tap doesn’t always mean a solid ground. Subterranean -unless one is pushed, I think in falling off a 4’ high platform gravity is going to initially put you on the running rail not a center rail 5’ away. One’s arm could hit the center rail but it’s not going to be guaranteed because you’ll likely be trying to break your fall. -are the top exposed 3rd rails of elevated lines much better? Especially where they are forced to be on the platform side or worse on both sides. Both Chicago and the old NY els look poor because of their lack of a top cover but they got along. -I wouldn’t take 12-10 as covering electrocutions because it also covers people who get back up okay. In fact a quick Google also extended it to people walking on the catwalks, likely both tunnel and el. I think the usage is to get them chased off (into a police cruiser). It strikes me that a person who falls and gets electrocuted is likely to become a 12-9. It was the lack of qualifiers in 12-9 reports that made me think that the timing of the fall was more deadly than what they might touch in the fall. -as far as public perceptions about rails goes I wouldn’t give them that much credit for something they don’t understand. If they read electric and railroad in the same sentence they think the whole railroad is dangerous. -When I was in the utility business, we didn’t worry about the degrees of exposure to people who were where they shouldn’t be, we just worried about them being there at all. The most frustrating case was a neighboring utility that found a high academic college student dead inside a totally enclosed station How do you design away that sort of risk? Have the burglar alarm shut down the whole station? We would not choose one buswork construction over another because of trespasser risks. Because even for our own worker risks all construction forms had their dangers. The differences were small compared to the fact that there was risk at all. Bill PS -that patent is an elaboration on basics. Put an ammeter in the lead from the resistors to ground, anything over milliamps means there’s dirty insulators leaking from one of the power rails. |
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Posted by Subterranean Railway on Sat Sep 12 17:02:17 2009, in response to Re: Fourth Rails and Safety, posted by Bill West on Sat Sep 12 15:59:02 2009. unless one is pushed, I think in falling off a 4’ high platform gravity is going to initially put you on the running rail not a center rail 5’ away.The physics of a falling human body are fairly complicated (a possible forward component of motion if the person were walking, a constantly changing moment of inertia that complicates calculations of how a person will rotate as (s)he falls, etc . . . ) Nonetheless, I think it's fairly safe to say that the further away a potential source of electrocution, the better. Especially where they are forced to be on the platform side or worse on both sides. As I said before, those are also rather dangerous. Three-track, two island platform stations are but one example in New York that comes to mind. are the top exposed 3rd rails of elevated lines much better? The lack of a top cover is actually safer, since it's harder to trip and fall while stepping over the third rail. (I've seen third rail protection boards bear workers' weights, but I know the practice is greatly frowned upon.) I wouldn’t take 12-10 as covering electrocutions because it also covers people who get back up okay. I didn't interpret it that way either. I merely used 12-10 to mean "persons on roadbed (or catwalk)" in general. My point was that 12-10s in London would be far less survivable than those in third rail-based systems, which are a fairly frequent occurrence (as I said, the vast majority of people on the roadbed, whether their presence be accidental or otherwise, slip by completely unreported.) It was the lack of qualifiers in 12-9 reports that made me think that the timing of the fall was more deadly than what they might touch in the fall. Again, it's not NYC I'm especially concerned about in that regard, it's London. You're correct in pointing out that electrocutions in NYC are fairly rare, since one'd have to be severely disoriented (or thrown hard) to touch the third rail in most cases. we didn’t worry about the degrees of exposure to people who were where they shouldn’t be, we just worried about them being there at all. I'm not talking about the safety of some high voltage switch room deep in a tunnel, but rather something that's very readily accessible. The fact is, people do frequently accidentally end up on the roadbed; not so much in the "totally enclosed station" you used in your example. To grossly hyperbolize your logic, it would be totally fine if the roadbed were ballasted with shards of broken glass and rusty nails. If people shouldn't be there at all, who cares about how safe it is? People shouldn't crash their cars, so why bother with safety features? ;-) that patent is an elaboration on basics. I didn't really care about whatever data were trying to be measured, I just liked the patent description because it described London's system of electrification fairly well. |
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Posted by Subterranean Railway on Sat Sep 12 17:07:29 2009, in response to Re: Fourth Rails and Safety, posted by Subterranean Railway on Sat Sep 12 17:02:17 2009. as I said, the vast majority of people on the roadbed, whether their presence be accidental or otherwise, slip by completely unreportedI should qualify this: they slip by unreported because they get out okay without any employee seeing, not because the MTA doesn't report them. |
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Posted by SelkirkTMO on Sat Sep 12 17:27:19 2009, in response to Re: Fourth Rails and Safety, posted by Bill West on Sat Sep 12 15:59:02 2009. Yeah, think I've got it now. LU didn't want any traction return current flowing through ground. But the bipolar thing just didn't add up. |
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Posted by Bill West on Sat Sep 12 21:20:46 2009, in response to Re: Fourth Rails and Safety, posted by Subterranean Railway on Sat Sep 12 17:02:17 2009. -bare top rails.... my choice is that I’d rather step over a tall top cover than over a medium bare rail. I’m thinking of where I would fall if anything went wrong.-buried substation.... most of my stations were outdoors. If someone got through the fence we didn’t try to regulate the degree of defenses inside, we’d already failed. There are just too many different ways for him to end up hurt once he breaks in for us to try and choose meaningful defenses. -shards of glass.... in the safety approach I mentioned the equivalent argument would be that if there is a need to have the glass there, then don’t debate the sharpness of glass, debate ways to keep people from falling. ie platform door systems. -car “safety”.... political programs are not something I’d take up in a scientific debate. Bill |
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Posted by Dan Lawrence on Sun Sep 13 11:52:46 2009, in response to Re: Fourth Rails and Safety, posted by Subterranean Railway on Sat Sep 12 09:57:19 2009. Saved it for later. Noted the patent date is 1999 in the US. Is there an earlier date for LU? |
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Posted by R36 #9346 on Sun Sep 13 12:09:49 2009, in response to Re: Fourth Rails and Safety, posted by Broadway Lion on Fri Sep 11 22:20:44 2009. Close. It's actually 630VDC, with the center rail at -210V, and the outside rail at +420V. |
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