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4th rail in 4ft at Northam junction

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pompeyfan

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As per the title, can anybody explain why there is a rail secured the the sleepers in the 4ft on the curve at Northam junction?
 
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swt_passenger

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I think it's something to do with improving the return current path, or increasing track circuit reliability, rather than relying only on the jointed track on the tight radius curve.

I saw a discussion in the signal box forum a while ago that attempts to explain it here:

http://forum.signalbox.org/viewtopic.php?f=5&t=4628

You can see that it is bonded to the running rails here and there. I assume it is 'simulating' something specific, or else why wouldn't they just use a big parallel cable? It's also right alongside a DC traction supply point, that gets mentioned in the linked discussion.
 
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Joseph_Locke

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Within earshot of trains passing the one and half
I think it's something to do with improving the return current path, or increasing track circuit reliability, rather than relying only on the jointed track on the tight radius curve.

I saw a discussion in the signal box forum a while ago that attempts to explain it here:

http://forum.signalbox.org/viewtopic.php?f=5&t=4628

You can see that it is bonded to the running rails here and there. I assume it is 'simulating' something specific, or else why wouldn't they just use a big parallel cable? It's also right alongside a DC traction supply point, that gets mentioned in the linked discussion.

A bit of 150lb con rail is much cheaper and far larger cross section than any cable ...
 

swt_passenger

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A bit of 150lb con rail is much cheaper and far larger cross section than any cable ...

Suppose it is, and also probably much less attractive to copper thieves.

Probably available in secondhand condition in reasonable quantities locally at the time they installed it as well.
 

pompeyfan

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Cheers for the answers. SWT passenger you seem very knowledgeable about the SWT network from this and other threads, where does your knowledge come from?
 

theageofthetra

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There is one on the Hayes branch for the same reason I believe though beside the rail not in the 4ft.
 

edwin_m

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No it isn't. There are normal check rails as well, this is in the middle of the four foot, resting on the sleepers.

That's known as a guard rail, and is fitted if there is a particular extra hazard if a train derails for any reason, most commonly the risk of falling off a viaduct. It provides an extra means of keeping the derailed train roughly in line with the track. I don't think there is any such hazard at Northam.

A check rail is close to the running rail on the inside of a tight curve or in areas of pointwork. The back of the flange contacting the check rail stops the opposite wheel climbing over its rail.
 

najaB

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It provides an extra means of keeping the derailed train roughly in line with the track. I don't think there is any such hazard at Northam.
There is, however, likely a need to improve the return current path as posted above.
 

randyrippley

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That's known as a guard rail, and is fitted if there is a particular extra hazard if a train derails for any reason, most commonly the risk of falling off a viaduct. It provides an extra means of keeping the derailed train roughly in line with the track. I don't think there is any such hazard at Northam.

A check rail is close to the running rail on the inside of a tight curve or in areas of pointwork. The back of the flange contacting the check rail stops the opposite wheel climbing over its rail.

But don't guard rails normally come in pairs? With tapered ends to "direct" the derailed wheelsets?
 

swt_passenger

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That's known as a guard rail, and is fitted if there is a particular extra hazard if a train derails for any reason, most commonly the risk of falling off a viaduct. It provides an extra means of keeping the derailed train roughly in line with the track. I don't think there is any such hazard at Northam.

A check rail is close to the running rail on the inside of a tight curve or in areas of pointwork. The back of the flange contacting the check rail stops the opposite wheel climbing over its rail.

I wasn't clear enough, I was not referring to a guard rail. My earlier post should be read as saying that the additional rail is definitely not a check rail. There are ALSO normal check rails on the curve and these are NOT the additional rail under discussion. I'll clarify the earlier post.
 
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Ships

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But don't guard rails normally come in pairs? With tapered ends to "direct" the derailed wheelsets?

Not always, at man pic platform 14 because of the restricted nature of the viaduct we were looking at a solution with a check and single guard rail. Currently it only has 1 in the 4ft
 
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