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Post by liamharrison72 on Jun 23, 2010 22:17:23 GMT
Hi there. When you are on a train and you look at the side of the tunnel you see two thin wires that run along the line at about shoulder level when standing up on the train. From what ive gathered these two wires turn the power off to the rails when connected together and is done so by using a tool usually carried in the drivers cabin. Why where these originally installed on the system? Do track workers also carry the tool to turn the power off to the rails incase of an emergency? Why hasnt the whole system got them and why does it only seem to be in tunnels? Can a track worker use their hands (no insulation/gloves) to turn the power off by touching them together or just by placeing their hands on both wires which would cause a link via the hand? If a train was coming and towards a track worker ( I hope this never ever happens) can he touch them together and if the power does turn off will the train just come to an immediate halt or will the train just slow down? And would the track engineer get a shock by touching the two wires with his bare hands? Is it enough voltage to kill him or just give him a nasty shock? Will the wires always be on the system or with all this upgrade work will some new method of current control be installed? Its a lot of question  sorry but it has been on my mind for a while and when i ask a question/want to know about something I liek to know everything and sometime get scenarios in my head which then just need to be answered / They call it OCD. ;D We all experience it in someway or other.  Thanks.  |
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Post by harlesden on Jun 23, 2010 22:53:46 GMT
I was told during my own training that the two wires can be squeezed together using your bare hand and any shock will be minimal.
Fast way to discharge traction current in an emergency.
A track worker should not really be in a tunnel if he/she is aware of the traction current being on.
A track working gang in the open air includes a dedicated lookout, watching for trains to warn his gang of an approaching train and to let the driver know his presence is acknowledged. I cannot say whether a lookout is needed for a gang working below the surface.
The two wires (tunnel telephone wires) provide an additional margin of safety and are unlikely to be modified.
I am happy to be corrected in any of the above.
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Post by Deleted on Jun 24, 2010 3:41:49 GMT
You're spot on. They're Tunnel Telephone wires. Pinching and rubbing them together should switch off traction current (unless the system is disabled, signage at the platform end is then in place). Contact must be made with the Service Controller within seven minutes to tell them why you want the traction current off. Or it'll get switched back on!
If the traction current were to be turned off trains do not automatically stop.
A few years back in the Metronet staff magazine, they said that with the advent of the Connect 2000 digital radios, they were looking forward to the Tunnel Telephone system not being in place one day in the future. This may have just been wishful thinking on their part though.
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Chris M
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Post by Chris M on Jun 24, 2010 9:04:14 GMT
I think it was realised that it's a useful backup system. Certainly that's why the LU tunnel telephone wires were left up and operable in the Thames Tunnel, even though it's not a system normally used on NR.
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Colin
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Post by Colin on Jun 24, 2010 15:32:02 GMT
Given that the tunnel telephone wire system is used to provide enhanced line clear protection during engineering hours, as required by HMRI, I very much doubt any serious consideration could/would be given to their removal.
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Post by Chris M on Jun 24, 2010 16:49:36 GMT
Well certainly not without putting an alternative system in place, but given that the tunnel telephone system is there, established, working and (presumably) reliable I can't see that replacing it would provide any benefit to anyone. So even if a formal evaluation of the cost-benefit ratio would come out in favour of retaining it when the ratio is: Benefits: "almost none at best", Cost is "lots".
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Post by District Dave on Jun 24, 2010 21:02:24 GMT
Just to add a small point to this, you will have noted that the system is named the 'Tunnel Telephone Wires' - in the OP there is also mention of a piece of equipment that can be used to activate these wires.
This is a telephone handset carried in train cabs and this serves a two fold purpose:
1) When the telephone handset is clipped to the two wires it will switch off traction current as described above and
2) It provides a means of communication to the Service Controller.
The wires are also sometimes referred to as 'pinch and rub' wires, for the simple reason that that is what you do with them - pinch them together and rub them together to ensure they work - you will know this as tunnel lighting should illuminate.
It used to be possible to try the system out in the London Transport Museum at Covent Garden - there used to be a section of tunnel there which showed a variety of equipment typically installed in a tunnel. Not sure if it's still there since the museum was renovated.
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Post by Chris M on Jun 24, 2010 23:00:37 GMT
I don't recall seeing anything like that when I visited the Covent Garden museum couple of months back.
I was going to comment further on the museum here, but realised it was getting very off topic, so I'm going to start a new thread for that.
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Post by Tomcakes on Jun 25, 2010 6:09:04 GMT
It used to be possible to try the system out in the London Transport Museum at Covent Garden - there used to be a section of tunnel there which showed a variety of equipment typically installed in a tunnel. Not sure if it's still there since the museum was renovated. It's no longer there. The space it used to occupy is now taken up by a large gallery with pictures of the NYC Subway etc which is naturally ten times more vital. |
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Post by Deleted on Jul 3, 2010 19:32:32 GMT
Just to add a small point to this, you will have noted that the system is named the 'Tunnel Telephone Wires' - in the OP there is also mention of a piece of equipment that can be used to activate these wires. This is a telephone handset carried in train cabs and this serves a two fold purpose: 1) When the telephone handset is clipped to the two wires it will switch off traction current as described above and 2) It provides a means of communication to the Service Controller. The wires are also sometimes referred to as 'pinch and rub' wires, for the simple reason that that is what you do with them - pinch them together and rub them together to ensure they work - you will know this as tunnel lighting should illuminate. Just to add two things to this - firstly that there are also telephones provided on station headwalls linked into the same circuits and for the same purpose, which can be used for emergency discharge of traction current; secondly that tunnel lighting being on should NEVER, EVER be taken as confirmation of traction current discharge (although it does usually come on when the current goes off, it can be switched on for other reasons), confirmation should always be sought from the controller. |
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sorry but it has been on my mind for a while and when i ask a question/want to know about something I liek to know everything 
