Platform Edge Power Switches

[rosswilson]

Hi Everyone,

I noticed something today whilst waiting at Lancaster platform 4 that I thought you could help me with. At a few stations i've visited there are switches all along the platform almost at track level. I have attached a photo that I managed to find to illustrate.

These switches appear to be like "firemans switches" that you find on the outside of commercial buildings. Does anybody know what these are for?

At first I thought the switches might be used in the event that somebody or something fell onto the track, but as the WCML is OHLE that chain of thought left me.

Maybe they have something to do with the track circuits? It's the fact that there are a lot of them, all evenly spaced approx 10m apart that interests me.

Ross

 

[RyanB]

it's kinda difficult to tell what it is from that picture, if the photo was bigger, it may be easier to tell what it actually is.

 

[ralphchadkirk]

I suspect he's meaning datum plates, but without a larger photo I've no idea.

 

[jopsuk]

I think we need the thread that explains the datum plate/sliders made a "sticky"

 

[sutty]

For years I wondered and I found out (from this forum, might I add) they're indeed "datum plates"

More info, here

http://www.railway-technical.com/track.shtml

 

[Hydro]

I swear I've installed hundreds of these buggers. Bane of my life at one point.

 

[sutty]

I swear I've installed hundreds of these buggers. Bane of my life at one point.

As a child I always thought they were switches as I saw some mounted on OHLE. Then I saw one mounted on a brick and one on a wooden post and I was curious for many years until I found this place.

 

[Snapper]

Datum plates or markings serve as a physical reminder of substandard clearances.


http://www.railway-technical.com/track.shtml

Substandard clearences?

That's not the explanation given...

"Monuments and Datum Plates

Along the line of route various locations are marked by a fixed post in the track or a plate on a nearby structure to indicate the correct level or position of the track. These are called monuments or datum plates. Measurements are taken from these to confirm the correct position of the track.

In the case of stations they ensure that the position of the track aligns with the platform to create the correct distance and height.

http://www.railway-technical.com/track.shtml

Here's a better picture of a datum plate:

http://paulbigland.pikfu.net/set111031/media63465198.html

 

[ralphchadkirk]

They don't serve as a reminder of substandard clearances, but they only need to be in place where there is a structure within a certain distance from the track IIRC. Hydro would be able to confirm.

 

[sutty]

They don't serve as a reminder of substandard clearances, but they only need to be in place where there is a structure within a certain distance from the track IIRC. Hydro would be able to confirm.

That'll teach me to copy and paste from Google whilst almost missing my stop on the train. My apologies

 

[ralphchadkirk]

That'll teach me to copy and paste from Google whilst almost missing my stop on the train. My apologies

Don't take my post as gospel, I'm not entirely sure, but someone like Hydro would be able to confirm.

 

[rosswilson]

Hi Guys,

Thanks for your replies, although I still believe these "plates" are something electrical related due to the presence of a "On/Off Switch".

I have managed to track down a photo of Lancaster platform 3: http://www.flickr.com/photos/estaga/5334070711/sizes/o/in/photostream/. Open the Full Sized version of that photo on Flickr and look between the track surface and the top of the platform edge. See those white plates (approx 8 inches tall) with vertical switches on the right?

There are 3 of them in that photo, all spaced evenly apart. It's interesting to note that the rightmost one is partially buried under the ballast.

Do we still think these are Datum Plates?

Ross

 

[OxtedL]

Yup, it's a datum plate.

The "switch" to which you refer is moved up or down (originally) to show the track level, and does not switch.

Check out any of the previous threads on this.

Try http://www.railforums.co.uk/showthread.php?t=44972 or http://www.railforums.co.uk/showthread.php?t=41255

Or http://www.railforums.co.uk/showthread.php?t=20924 .

Or http://www.railforums.co.uk/showthread.php?t=39072 .

Or http://www.railforums.co.uk/showthread.php?t=28790 .

 

[AlterEgo]

I can't believe how many times people ask this question. Certainly it bugged me for years until I found this forum! Perhaps all future datum plates should have "I AM A DATUM PLATE" written on them?

 

[Hydro]

Datum plates go on any structure or installation within a certain distance of the track. I can't remember the specifics on how near right now, it was a while ago now and I'm full of food and tired. There are two types, shown by the coloured sliders. Red denotes that the plate details can be changed to reflect any track movement and that the track need not be realigned as long as safe correct clearances are maintained. Green shows that the information on the plate must be adhered to, they are the design measurements. If the track moves, then the track MUST go back to the measurements on the plate via lifting or sluing. This concept is known as Absolute Track Geometry, you always have to keep the track to it's original design. This is to maintain tight clearances, like platforms or close structures. Platforms should start to have all green sliders to maintain the correct clearances. Plates are normally mounted every ten metres on platforms and long structures, or at the beginning and end of short ones. The details on the plate are:

Cant at the plate location, distance to nearest running rail gauge face, abbreviated name of the nearest track (UF, DF, US etc), plate number and the slider is set so that the top edge is level with top of the nearest running rail. There's a red square that serves as the constant measurement point, you measure from the inside edge of the rail to the top of the square.

I've probably missed something out, way too full of cherry pie right now to remember all of my structure gauging theory.

 

[ess]

and yet despite the fact someone will have done all the calculations, you still have to mind the gap - why aren't platforms the same heights and why aren't the floors of trains always the same distance above the rails?

 

[Hydro]

and yet despite the fact someone will have done all the calculations, you still have to mind the gap - why aren't platforms the same heights and why aren't the floors of trains always the same distance above the rails?

Curves and cant (and vehicle dimensions) affect how big the gap will be. There's no one measurement for the x and y dimensions, there's a maximum and a minimum. Older platforms will be lower, heavily canted track (like Clapham Junction) will lean the train closer or further from the edge depending on the hand of the curve...many factors.

 

[jopsuk]

Even on perfectly straight track, certainly at through platforms, almost gap-less (as found on the DLR) would not be desirable due to the motion of trains- plus, due to lack of strict standards, different stock is slightly different in width and floor height.

 

[swt_passenger]

I think we need the thread that explains the datum plate/sliders made a "sticky"

Get back in the queue, we need a XC HST diagram sticky first...