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What this on third rail ?

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waynemorrell

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Conductor rail on approach to London Bridge with some sort of yellow plastic covering underneath the rail.

04ED79EC-7597-4C76-BBD0-CBD9719CFBA3.jpeg

Hi,

Anyone know what this is on the third rail on approach to London Bridge?
 
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david737

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If you look carefully there is some writing on the insulation that reads 'short circuiting bar not to be used', these yellow strips are placed in locations where using a bar might cause damage to signalling equipment/other parts of the infrastructure etc.
 

theageofthetra

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Looks like the conductor rail to me with some nice yellow insulation on the bottom of it.
Which after a while will be brown so it probably won't get noticed. The note about short circuiting bars is that presumably it won't work as its in contact with the insulation.

Anyone know why they are put there?
 

HSTEd

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Probably because it is a position considered more likely to come into contact with things that should not be in contact with the third rail.

Honestly I am surprised that the bottom and sides of all third rail is not insulated - the only surface that needs to be exposed is the top.
 

ComUtoR

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Honestly I am surprised that the bottom and sides of all third rail is not insulated - the only surface that needs to be exposed is the top.

The Short Circuit Bar is applied to the underneath.
 

D365

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Honestly I am surprised that the bottom and sides of all third rail is not insulated - the only surface that needs to be exposed is the top.

Cost and maintenance requirements one would assume.
 

swt_passenger

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Which after a while will be brown so it probably won't get noticed. The note about short circuiting bars is that presumably it won't work as its in contact with the insulation.

Anyone know why they are put there?
They are there specifically to warn you not to use the short circuit bar at that location. As stated in post #3, Usually seen in complex s&c areas because that specific running rail is not the normal traction return path, so the short circuit bar will cause avoidable damage.
 

DY444

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There are locations (usually around S&C) where the running rail nearest to the conductor rail doesn't carry traction return current. Hence trying to use an SCB will a. not work and b. cause havoc with signalling circuits and so the protective cover on the underside acts as a warning and a physical barrier to prevent the use of an SCB.

Edit. swt_passenger beat me to it!
 

theageofthetra

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There are locations (usually around S&C) where the running rail nearest to the conductor rail doesn't carry traction return current. Hence trying to use an SCB will a. not work and b. cause havoc with signalling circuits and so the protective cover on the underside acts as a warning and a physical barrier to prevent the use of an SCB.

Edit. swt_passenger beat me to it!
Unfortunately after about a year these yellow covers are as brown as the rest of the conductor rail and the writing is illegible.

I also struggle to think of drivers having ever been formally advised of this requirement in our notice cases- has anyone seen anything?
 

Llanigraham

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Unfortunately after about a year these yellow covers are as brown as the rest of the conductor rail and the writing is illegible.

I also struggle to think of drivers having ever been formally advised of this requirement in our notice cases- has anyone seen anything?
See post #6.
 

swt_passenger

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Unfortunately after about a year these yellow covers are as brown as the rest of the conductor rail and the writing is illegible.

I also struggle to think of drivers having ever been formally advised of this requirement in our notice cases- has anyone seen anything?
It is included in the DC electrified lines module of the rule book, section 6.3
 

coppercapped

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Conductor rail on approach to London Bridge with some sort of yellow plastic covering underneath the rail.

View attachment 43105

Hi,

Anyone know what this is on the third rail on approach to London Bridge?
Speaking as a non-railwayman, but as one who knows a little bit about electricity, it looks to me like an insulator to reduce leakage currents from the third rail to earth. I notice that it is attached to the ramped end of the third rail where the clearance between the bottom of the 'bent down' section and the ballast will be minimal. As it is known that a lot of the third rail amps just leak away without driving a train it looks to me to be a simple way of minimising such losses at the point where leakage is very likely to occur, especially if the ballast is wet.
 

swt_passenger

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Speaking as a non-railwayman, but as one who knows a little bit about electricity, it looks to me like an insulator to reduce leakage currents from the third rail to earth. I notice that it is attached to the ramped end of the third rail where the clearance between the bottom of the 'bent down' section and the ballast will be minimal. As it is known that a lot of the third rail amps just leak away without driving a train it looks to me to be a simple way of minimising such losses at the point where leakage is very likely to occur, especially if the ballast is wet.
No, the reason is as given in earlier posts by David737, myself and DY444 as above.
 

Signal Head

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No, the reason is as given in earlier posts by David737, myself and DY444 as above.

If it is intended to prevent SCB use it should extend to an insulated joint (in the running rail) since that's where the 'signalling' and traction return rails will swap over. There is no IRJ visible near the end of the guard, so I suspect it might, as coppercapped suggested, be there to prevent a short circuit to earth in an area of reduced clearance.
 

furnessvale

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Serious question. I see this guard is fitted in an area where the third rail is dipping towards the ground. Would the changed angle between running rail and third rail this causes have any bearing on the deployment of an SCB?
 

swt_passenger

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If it is intended to prevent SCB use it should extend to an insulated joint (in the running rail) since that's where the 'signalling' and traction return rails will swap over. There is no IRJ visible near the end of the guard, so I suspect it might, as coppercapped suggested, be there to prevent a short circuit to earth in an area of reduced clearance.
From what I’ve seen the sections of strips can ‘walk’ along the foot of the con rail. The gap at the left may be the explanation for the strip extending beyond the end of the ramp...
 
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