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| Re: Fourth Rails and Safety (832319) | |||
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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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