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| Re: Fourth Rails and Safety (832563) | |||
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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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