What are these? (Train stuff)

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4p

4p

4p

Soldato
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See them all the time at stations. Looks like a slider is on it.
 
Volume control for the clickety-clack. They turn it down at night.

Interesting question actually... though I suspect the answer will be less satisfying than guessing. :-)
 
Datum plates are fixed to structures (platforms, bridges and overhead line masts, etc.) located near the track. The details on the plate specify the relative position of the track, so that it can be monitored for movement.

Figure 6 shows a datum plate identified as chainage point number (C.P.N°) 58. The letters "DN" (on a red background) denote that the information on the plate relates to the Down line. "Offset" is the horizontal distance from the plate to the running edge ("R.E.") of the nearest rail of the relevant track, in this case 2915 mm. The track is canted at 35 mm. The top of the movable slider block is normally set at the level of the nearest rail. If it is necessary to fix the datum plate at a higher level than the track, the number above the slider block indicates the difference in height between the rail head and the slider block (300 mm in the example illustrated).

A red slider block means that the data on the plate refers to the actual position of the track at the time when the datum plate was installed. A green block denotes a track design position, to which the track should be returned in the event of it moving out of alignment.
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Looks like I was right. :-) Thank neo, it all makes sense now. I guess we'll have to strike that off the list of things to ponder when waiting for trains.
 
Eames said:
If you stepped on tracks such as those in the london underground would you actually be electrocuted?
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Yes, if they are live rails.

The London Underground system has two direct current live rails. Much of the national rail system south of London (and also Merseyrail) have a single DC live rail. The national rail system is 750v DC.

If you step on these then there is a very strong chance you will be either very seriously hurt or killed.

On the rest of the network the rails are not live and you will not be electrocuted if you stand on them, though it's still dangerous and stupid and a criminal offence to tresspass on the railway.
 
[TW]Fox;24434120 said:
If they are correctly insulated perhaps but why would you ever want to test that theory? There is no reason for anyone to ever stand on a conductor rail.
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If you stand on the live rail with both feet on it you will not be electrocuted most likely. However, if you lose balance and one foot goes on the ground you will then be electrocuted.
 
[TW]Fox;24434120 said:
If they are correctly insulated perhaps but why would you ever want to test that theory? There is no reason for anyone to ever stand on a conductor rail.
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I work on the railway and was told that the voltage on Overhead line equipment can jump up to 9 feet so I doubt that an inch of rubber sole would protect you much,not 100% sure about live rails as we don't have them in Scotland.
 
Monkeynut said:
If you stand on the live rail with both feet on it you will not be electrocuted most likely. However, if you lose balance and one foot goes on the ground you will then be electrocuted.
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Gotta complete the curcuit :)
 
LU features two conductive rails to stop the return current from flowing through any metal tunnel linings which might be damaged :)
 
Third rail is all over the place not just in london underground. It's basically looks like just an extra rail on the track and the train can get electricity from it as and when it needs it.

You can usually tell when its live as there will be dead wildlife near it, squirrels etc. :o
 
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