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1 hour ago, jim.snowdon said:

 how many people have, for example, seen what at 750V DC short circuit looks like, or have ever seen a short circuiting bar used on the real railway?

 

Jim

Me, and I have paddled up from a live rail, you soon learn respect for the 3rd rail as you lift the last shoe and it draws a lovely arc which you have to break with the paddle.

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9 hours ago, The Stationmaster said:

Even more worrying than that in my view with a sub-contracted man working in an area of which he seemed to have very limited knowledge and where he received no briefing at the site.  I would also wonder about the level of assessment NR had applied to the contractor before accepting them for online work as the contractor's supervision of working hours in a safety critical person would seem to be lacking to say the very least.

 

Alas an incident that was regrettably bound to happen sometime or other notwithstanding all the extra paperwork and procedures now in use for possessions and staff working on or about the line - very worrying.

In the early days of privatisation we were very short staffed and encouraged to use agency staff as Lookout, COSS, etc. 

I used to go out with my staff to do audits on my projects and on more than one occasion stopped the job from going ahead as I was not satisfied that the person supplied by the agency was competent and had any prior knowledge of what was a quite tricky worksite.

On one occasion I turned up for a site survey at 10am and found the Lookout asleep in his van. He had a mattress and sleeping bag on the back and when I questioned him about his working hours it transpired that he hadn't been home for several days and had worked variable shifts in that time, some with only a few hours break between them. I cancelled the job, sent him away and the supplying company found itself in a bit of bother.

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2 hours ago, royaloak said:

Me, and I have paddled up from a live rail, you soon learn respect for the 3rd rail as you lift the last shoe and it draws a lovely arc which you have to break with the paddle.

You're not the only one - it was standard practice when I was an engineer with LU to pull the shore plugs out with the auxiliaries still running, although we did normally wait for the compressor to stop first. We used to plug them in direct onto the auxiliary loads, compressor included, and the simple rule was to get the plug in and fully home smartly.

However, back to today's railway, and I suspect I would be hard pressed to find a conductor rail strap man who had any practical experience of an actual short circuit, and thus appreciated the need for testing and putting a bar down before finally clamping the end of the short circuiting cable (strap) onto the conductor rail. Instead, the fact that by the time they come to apply the strap it is always dead (or rather, nearly always dead) breeds complacency and the absence of knowledge of what can actually happen when, for once it isn't (or you are in the wrong place) results in a diminution of respect for that extra rail. Telling them that it is dangerous doesn't have the same effect as seeing the power that can be unleashed.

 

Jim

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3 hours ago, TheSignalEngineer said:

In the early days of privatisation we were very short staffed and encouraged to use agency staff as Lookout, COSS, etc. 

I used to go out with my staff to do audits on my projects and on more than one occasion stopped the job from going ahead as I was not satisfied that the person supplied by the agency was competent and had any prior knowledge of what was a quite tricky worksite.

On one occasion I turned up for a site survey at 10am and found the Lookout asleep in his van. He had a mattress and sleeping bag on the back and when I questioned him about his working hours it transpired that he hadn't been home for several days and had worked variable shifts in that time, some with only a few hours break between them. I cancelled the job, sent him away and the supplying company found itself in a bit of bother.

 

That is very much in line with the experiences of one of my cousins. Any amount of dodgy practices going on then.

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2 hours ago, jim.snowdon said:

You're not the only one - it was standard practice when I was an engineer with LU to pull the shore plugs out with the auxiliaries still running, although we did normally wait for the compressor to stop first. We used to plug them in direct onto the auxiliary loads, compressor included, and the simple rule was to get the plug in and fully home smartly.

However, back to today's railway, and I suspect I would be hard pressed to find a conductor rail strap man who had any practical experience of an actual short circuit, and thus appreciated the need for testing and putting a bar down before finally clamping the end of the short circuiting cable (strap) onto the conductor rail. Instead, the fact that by the time they come to apply the strap it is always dead (or rather, nearly always dead) breeds complacency and the absence of knowledge of what can actually happen when, for once it isn't (or you are in the wrong place) results in a diminution of respect for that extra rail. Telling them that it is dangerous doesn't have the same effect as seeing the power that can be unleashed.

 

Jim

Didn't I read recently that you're not allowed to use the indicator lamp boxes on the Southern any more for some "safety-related" reason?

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6 hours ago, St Enodoc said:

Didn't I read recently that you're not allowed to use the indicator lamp boxes on the Southern any more for some "safety-related" reason?

The "egg-boxes" were replaced about 5 years ago with a more modern equivalent tester/indicator.

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That's right. They were not fail safe as a safe indication was that the bulbs were not lit. There were a few cases of the bulbs not lighting due to a fault or incorrect use giving a false clear.

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For those that haven't seen one, a couple of images of the old 'egg-box' tester that is no longer used to check if the 3rd rail is live.

 

This one indicating the 3rd rail current is switched off.

P1000501.JPG.edab9258886af22ed2775ce1e05f098b.JPG

 

And this one indicating the 3rd rail is "LIVE".

P1000502.JPG.d632f7bf6cd864ae961793b516b97386.JPG

 

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53 minutes ago, Titan said:

That's right. They were not fail safe as a safe indication was that the bulbs were not lit. There were a few cases of the bulbs not lighting due to a fault or incorrect use giving a false clear.

The Electricity at Work Regulations require any portable device used to prove a conductor is dead to be demonstrated to be working before and after the test to prove dead. The only way to do that with the lamp box was to put it on a known live conductor rail on another track, assuming that there is even one available. At the very least, that exposes the person using the device to danger from the live conductor rail, and at worst, moving trains on a still open line. Exposing people to unnecessary danger is not legally tolerable. 

Modern conductor rail testers (live line testers) are either self-testing, using an internal safe voltage source, or are supplied with a separate, easy portable, test unit. That allows the user to demonstrate safely that the live line tester works before and after the actual conductor rail test is undertaken.

 

Jim 

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Posted (edited)
59 minutes ago, jim.snowdon said:

The Electricity at Work Regulations require any portable device used to prove a conductor is dead to be demonstrated to be working before and after the test to prove dead. The only way to do that with the lamp box was to put it on a known live conductor rail on another track, assuming that there is even one available. At the very least, that exposes the person using the device to danger from the live conductor rail, and at worst, moving trains on a still open line. Exposing people to unnecessary danger is not legally tolerable. 

Modern conductor rail testers (live line testers) are either self-testing, using an internal safe voltage source, or are supplied with a separate, easy portable, test unit. That allows the user to demonstrate safely that the live line tester works before and after the actual conductor rail test is undertaken.

 

Jim 

 

One advantage that immediately springs to mind with the 'box of eggs' is that should ECRO (or indeed a train bridge two electrical sections) cause the con rail to become live then you get an instant notification of the fact. Its all very well making sure the con rail is dead at the start of the work but we all know mistakes can happen and it is very unwise to assume the con rail will stay that way*. By contrast the various portable testers in use now DON'T offer that protection even if they are 'safer to use.

 

On the plus side though, this deficiency seems to have been noted as in recent cases where I have seen a MOM take a temporary isolation involving hook switches (which is probably where the greatest room for error occurs) they use a modern equivalent of the box of eggs which they place on the con rail BEFORE it gets switched off that has a flashing light on it. When the conductor rail is de-energised the light goes off - but should the con rail become live again then the device starts flashing again.

 

* Those of us who mainly work under lookout protection will never totally trust 'line blockages' to keep us safe (i.e. we always keep looking up while working under line blocks + avoid touching the con rail) - and by contrast ,those who normally only work under line blockage protection sometimes display an alarming lack of awareness when they end up working on an open line.

Edited by phil-b259
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8 minutes ago, phil-b259 said:

One advantage that immediately springs to mind with the 'box of eggs' is that should ECRO (or indeed a train bridge two electrical sections) cause the con rail to become live then you get an instant notification of the fact. Its all very well making sure the con rail is dead at the start of the work but we all know mistakes can happen and it is very unwise to assume the con rail will stay that way*. By contrast the various portable testers in use now DON'T offer that protection even if they are 'safer to use.

If the isolated con rail is then bonded to a return rail, if the current does then become live the protection will take it back out. If you're touching the rail during that 50ms then that's not good news, but the same applies with the eggs (which wouldn't work anyway if the con rail is shorted to neutral).

 

Not something you want to happen, of course, but it only takes one of those bulbs to blow (they're 6 x 110V in series, right?) in the egg box and it's lying to you about the line being dead, so I wouldn't be happy to rely on it anyway.

 

I suppose this is partly what the NSCDs are about.

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The comments about contractors and sub-contractors are interesting to say the least and the big problem is really down to poor/lack of assessment of contractors by NR and imposing what are often bureaucratic procedures on staff who might not have been well trained in them.  As a matter of historical fact much of the PerWay maintenance work, including some patrolling, on much of the London Division of the WR was in the hands of private contractors (mainly Grant Lyon Eagre) back in the 1960s reportedly due to recruitment problems getting staff for BR.  But it was of course supervised by experienced PerWay Inspectors who had the responsibility for the maintenance of track on their respective patches.

 

I don't think the contractors involved back then were any worse (or any better) than BR direct employed staff doing the same job but the critical point was that there was close BR supervision of the standard of work even where the contractor had decided, for example, that additional Kango packing was needed and had carried on with it without further reference to the local supervisor.   Those contractors definitely brought in sub-contracted labour but no doubt as they were responsible for the work they did they made sure the people they employed were competent to do what was expected of them.

 

When wider contracting out of work at lineside etc (i.e. not PerWay or S&T work) began in the late 1980s the situation changed and the railway safety awareness of these newer contractors left a lot to be desired.  As the then District Inpsector at Reading said of one incident where a train hit a ladder with somebody on it  'For all that bloke knew about what he was doing I might as well give my dog a can of dog food and tell him to open it himself'.  

 

The real need in my view is not necessarily for reams of 'back covering' paperwork but if contractors are to be used they might need close practical training and supervision.  The impression I get - illustrated in some respects by a gang we found on a non NR site some years ago - but claiming to be trained to NR standards and in any case supposedly working under NR operated signal protection - was a distinct lack of practical knowledge and an ability to parrot like answer questions on procedures with limited understanding of what they meant.  In that instance my oppo, working on safety matters for the site operator, gave them a suitable education in respect of their working and safety practices because he and I could see exactly what they had failed to do to protect their work site.  It is frightening if such things are happening out there with trains moving at considerable speed but I fear they are - as this particular incident illustrates.  And what price Hidden 18 among all this I wonder?

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Posted (edited)
1 hour ago, jim.snowdon said:

The Electricity at Work Regulations require any portable device used to prove a conductor is dead to be demonstrated to be working before and after the test to prove dead. The only way to do that with the lamp box was to put it on a known live conductor rail on another track, assuming that there is even one available. At the very least, that exposes the person using the device to danger from the live conductor rail, and at worst, moving trains on a still open line. Exposing people to unnecessary danger is not legally tolerable. 

Modern conductor rail testers (live line testers) are either self-testing, using an internal safe voltage source, or are supplied with a separate, easy portable, test unit. That allows the user to demonstrate safely that the live line tester works before and after the actual conductor rail test is undertaken.

 

Jim 

 

I use a  "Proving Unit" before using a Meter to carry out any testing. Similar to:- 

 

https://martindale-electric.co.uk/product/pd710-700v-dc-proving-unit/

Edited by Pannier Tank
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1 hour ago, jim.snowdon said:

The Electricity at Work Regulations require any portable device used to prove a conductor is dead to be demonstrated to be working before and after the test to prove dead. The only way to do that with the lamp box was to put it on a known live conductor rail on another track, assuming that there is even one available. At the very least, that exposes the person using the device to danger from the live conductor rail, and at worst, moving trains on a still open line. Exposing people to unnecessary danger is not legally tolerable. 

Modern conductor rail testers (live line testers) are either self-testing, using an internal safe voltage source, or are supplied with a separate, easy portable, test unit. That allows the user to demonstrate safely that the live line tester works before and after the actual conductor rail test is undertaken.

 

Jim 

Thanks Jim. That's a full and clear explanation of what I half-remembered. Evidence of absence rather than absence of evidence.

 

It certainly seem to provide a safer environment than the egg boxes did but I agree with phil-b259 that the loss of visual indication (even though there might be a false negative from a blown lamp or otherwise) is a pity.

 

By the way, when I first went to the Southern I was taught in no uncertain terms that the electrical thingies that provide illumination are "lamps", "lights" are bits of glass that you can look through and "bulbs" grow in the ground.

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36 minutes ago, The Stationmaster said:

The comments about contractors and sub-contractors are interesting to say the least and the big problem is really down to poor/lack of assessment of contractors by NR and imposing what are often bureaucratic procedures on staff who might not have been well trained in them.  As a matter of historical fact much of the PerWay maintenance work, including some patrolling, on much of the London Division of the WR was in the hands of private contractors (mainly Grant Lyon Eagre) back in the 1960s reportedly due to recruitment problems getting staff for BR.  But it was of course supervised by experienced PerWay Inspectors who had the responsibility for the maintenance of track on their respective patches.

 

I don't think the contractors involved back then were any worse (or any better) than BR direct employed staff doing the same job but the critical point was that there was close BR supervision of the standard of work even where the contractor had decided, for example, that additional Kango packing was needed and had carried on with it without further reference to the local supervisor.   Those contractors definitely brought in sub-contracted labour but no doubt as they were responsible for the work they did they made sure the people they employed were competent to do what was expected of them.

 

When wider contracting out of work at lineside etc (i.e. not PerWay or S&T work) began in the late 1980s the situation changed and the railway safety awareness of these newer contractors left a lot to be desired.  As the then District Inpsector at Reading said of one incident where a train hit a ladder with somebody on it  'For all that bloke knew about what he was doing I might as well give my dog a can of dog food and tell him to open it himself'.  

 

The real need in my view is not necessarily for reams of 'back covering' paperwork but if contractors are to be used they might need close practical training and supervision.  The impression I get - illustrated in some respects by a gang we found on a non NR site some years ago - but claiming to be trained to NR standards and in any case supposedly working under NR operated signal protection - was a distinct lack of practical knowledge and an ability to parrot like answer questions on procedures with limited understanding of what they meant.  In that instance my oppo, working on safety matters for the site operator, gave them a suitable education in respect of their working and safety practices because he and I could see exactly what they had failed to do to protect their work site.  It is frightening if such things are happening out there with trains moving at considerable speed but I fear they are - as this particular incident illustrates.  And what price Hidden 18 among all this I wonder?

The problem I see, Mike, is that when all the "experienced PerWay Inspectors" and the like leave, retire or drop off the hook, who is there to step into that role?

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51 minutes ago, phil-b259 said:

 

One advantage that immediately springs to mind with the 'box of eggs' is that should ECRO (or indeed a train bridge two electrical sections) cause the con rail to become live then you get an instant notification of the fact. Its all very well making sure the con rail is dead at the start of the work but we all know mistakes can happen and it is very unwise to assume the con rail will stay that way*. By contrast the various portable testers in use now DON'T offer that protection even if they are 'safer to use.

 

On the plus side though, this deficiency seems to have been noted as in recent cases where I have seen a MOM take a temporary isolation involving hook switches (which is probably where the greatest room for error occurs) they use a modern equivalent of the box of eggs which they place on the con rail BEFORE it gets switched off that has a flashing light on it. When the conductor rail is de-energised the light goes off - but should the con rail become live again then the device starts flashing again.

 

* Those of us who mainly work under lookout protection will never totally trust 'line blockages' to keep us safe (i.e. we always keep looking up while working under line blocks + avoid touching the con rail) - and by contrast ,those who normally only work under line blockage protection sometimes display an alarming lack of awareness when they end up working on an open line.

Phil,

 

I'm not unaware of that, and the wider issues of marking both live floaters (for the unitiated, sections of con rail, generally short, in pointwork that can remain live by virtue of being fed from another track to the one that is isolated) and as a general indicator. Forthcoming debates about standards for section proving DC after alterations to, or work on, the feeding arrangements are likely to provoke further debate on this.

 

40 minutes ago, Zomboid said:

Not something you want to happen, of course, but it only takes one of those bulbs to blow (they're 6 x 110V in series, right?) in the egg box and it's lying to you about the line being dead, so I wouldn't be happy to rely on it anyway.

 

I suppose this is partly what the NSCDs are about.

I haven't checked one personally, but two parallel strings of three bulbs would be more sensible. Even then, 3 x 230V bulbs might not last overly long on 850V, that being the level to which the conductor rail voltage can rise with everything off load. (3 x 230 is only 690, which is tight even for 750V, although it was probably tolerable on the Southern's original 660V.)

 

NSCDs (and the rather more upmarket Track Feeder Switches going in on the Liverpool and Watford lines) take a gtreat deal of the risk out of short circuiting the conductor rail, and doing it is a manner that is both not subject to the vagaries of how well the strap man tightened up the clamps and is secure within the meaning of the regulations by virtue of being locked by an electrically responsible person.

 

The NSCD only applies a short circuit and, via interlocks, prevents the ECO closing the circuit breaker. The Track Feeder Switch (TFS) goes one step further and disconnects the conductor rail from the substation feeder, which both protects against a circuit breaker closure and allows for the substation to be taken off line independently of the conductor rail status. It's what all the UK tramways, with the possible exception of the original parts of Metrolink) adopted as standard when they were built.

 

Jim

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1 hour ago, jim.snowdon said:

I haven't checked one personally, but two parallel strings of three bulbs would be more sensible. Even then, 3 x 230V bulbs might not last overly long on 850V, that being the level to which the conductor rail voltage can rise with everything off load. (3 x 230 is only 690, which is tight even for 750V, although it was probably tolerable on the Southern's original 660V.)

Bulbs working on a nominal 230v AC will have a range of 216.2v to 253v feeding them on the mains given the permitted tolerances. As this is the RMS value the actual peak can be up to approximately 358v. 

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16 hours ago, royaloak said:

... I have paddled up from a live rail, you soon learn respect for the 3rd rail as you lift the last shoe and it draws a lovely arc which you have to break with the paddle.

 

Any chance of an explanation of the above for the layman, please? 

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Posted (edited)
59 minutes ago, spikey said:

 

Any chance of an explanation of the above for the layman, please? 

During training we had to 'paddle up' a 3rd rail EMU on a live rail, they didnt want us to de-energise Clapham Yard for some strange reason, cant think why! ;)

This involves taking the WOODEN paddles (so called because they look a bit like canoe paddles) out of the cab and using one WOODEN paddle to lift the shoe off the 3rd rail, inserting another WOODEN paddle between the shoe and 3rd rail so the shoe is isolated and then lowering the shoe onto the second WOODEN paddle, when you lift the last shoe the electricity will jump across/arc from the 3rd rail to the shoe so you have to sweep the arc to break it with the second WOODEN paddle before placing it on the 3rd rail and lowering the shoe onto it, at that point you realise what sort of voltage/current you are dealing with.

 

But out on the mainline in a 'real world' situation this would normally only be done when the 3rd rail is short circuiting (there are other reasons but lets keep it simple) and is a way to find out if its a train causing the issue and then which train (there can be several in that electrical section) is the naughty one, obviously if all trains are paddled up and the 3rd rail is still short circuiting then the job is right royally messed up.

 

Lets assume there is a short so the 3rd rail is dead/isolated, all the drivers in that electrical section would be instructed to paddle up their trains and once confirmed with the signaller/electrical control officer the 3rd rail would be re-energised, if it is holding then it can be assumed a train is short circuiting the 3rd rail so now they need to find out which train, so one by one each driver would in turn be instructed to (gently) drop a shoe onto the 3rd rail to see what happens. If it isnt their train then all that would happen is there would be a quick 'zip' and everything on board the train would spring back into life, the driver says thank flip for that and can relax a little bit.

 

But (oh there is always a but) when the one which is causing the short circuit is re-energised there would be an almighty bang and the driver would know it was his train, swear under his breath as they now have a whole world of fault finding coming their way.

 

Basically it is a way of isolating trains from the 3rd rail to allow fault finding to take place and find out what is causing the short circuit.

 

As you can imagine this is a very long winded affair and takes ages but I have tried to keep things simple so the basic procedure can be understood and isnt lost in a world of different scenarios, I hope that clarifies things.

Edited by royaloak
Edited to keep the pedants happy, maybe they should have explained it themselves.
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6 minutes ago, royaloak said:

During training we had to 'paddle up' a 3rd rail EMU on a live rail, they didnt want us to de-energise Clapham Yard for some strange reason, cant think why! https://www.rmweb.co.uk/community/uploads/emoticons/default_wink.png

 

But out on the mainline in a 'real world' situation this would normally only be done when the 3rd rail is short circuiting (there are other reasons but lets keep it simple) and is a way to find out if its a train causing the issue and then which train (there can be several in that electrical section) is the naughty one, obviously if all trains are paddled up and the 3rd rail is still short circuiting then the job is right royally messed up.

 

Lets assume there is a short so the 3rd rail is dead/isolated, all the drivers in that electrical section would be instructed to paddle up their trains and once confirmed with the signaller/electrical control officer the 3rd rail would be re-energised, if it is holding then it can be assumed a train is short circuiting the 3rd rail so now they need to find out which train, so one by one each driver would in turn be instructed to (gently) drop a shoe onto the 3rd rail to see what happens. If it isnt their train then all that would happen is there would be a quick 'zip' and everything on board the train would spring back into life, the driver says thank flip for that and can relax a little bit.

 

But (oh there is always a but) when the one which is causing the short circuit is re-energised there would be an almighty bang and the driver would know it was his train, swear under his breath as they now have a whole world of fault finding coming their way.

 

Basically it is a way of isolating trains from the 3rd rail to allow fault finding to take place and find out what is causing the short circuit.

 

As you can imagine this is a very long winded affair and takes ages but I have tried to keep things simple so the basic procedure can be understood and isnt lost in a world of different scenarios, I hope that clarifies things.

...by placing a wooden (hence insulating) "paddle" between the collector shoe and the conductor rail.

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Posted (edited)
44 minutes ago, royaloak said:

... I hope that clarifies things.

 

Gosh, it does indeed.  Thanks very much for taking the trouble to post that very clear explanation.

 

ETA - I wouldn't fancy that for a lark if it was pouring down with rain ... 

Edited by spikey
afterthought

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6 hours ago, Zomboid said:

If the isolated con rail is then bonded to a return rail, if the current does then become live the protection will take it back out. If you're touching the rail during that 50ms then that's not good news, but the same applies with the eggs (which wouldn't work anyway if the con rail is shorted to neutral).

 

Not something you want to happen, of course, but it only takes one of those bulbs to blow (they're 6 x 110V in series, right?) in the egg box and it's lying to you about the line being dead, so I wouldn't be happy to rely on it anyway.

 

I suppose this is partly what the NSCDs are about.

The lamps in the egg box are wired in parallel. If one lamp fails, the remainder show a bit brighter. 

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3 hours ago, royaloak said:

But out on the mainline in a 'real world' situation this would normally only be done when the 3rd rail is short circuiting (there are other reasons but lets keep it simple) and is a way to find out if its a train causing the issue and then which train (there can be several in that electrical section) is the naughty one, obviously if all trains are paddled up and the 3rd rail is still short circuiting then the job is right royally messed up.

 

Lets assume there is a short so the 3rd rail is dead/isolated, all the drivers in that electrical section would be instructed to paddle up their trains and once confirmed with the signaller/electrical control officer the 3rd rail would be re-energised, if it is holding then it can be assumed a train is short circuiting the 3rd rail so now they need to find out which train, so one by one each driver would in turn be instructed to (gently) drop a shoe onto the 3rd rail to see what happens. If it isnt their train then all that would happen is there would be a quick 'zip' and everything on board the train would spring back into life, the driver says thank flip for that and can relax a little bit.

 

But (oh there is always a but) when the one which is causing the short circuit is re-energised there would be an almighty bang and the driver would know it was his train, swear under his breath as they now have a whole world of fault finding coming their way.

In today's world, with safety elves popping out from behind every structure, I suspect the paddling up of shoes would be undertaken only after the conductor rail had been made dead, and, assuming that that disconnected the fault and allowed the rail to be re-charged, it would be turned off again before any shoes were dropped back onto the rail, then re-charged. Plus, they would probably want an Emergency Switch Off on any adjacent road, and would require line blockages, just so that everyone is protected, not entirely without reason. Fortunately, short circuit faults on trains are not common, and short circuits in the train wiring between the shoe fuses and the shoes even less so. Normally, the expectation is that either the equipment fuse or, ultimately, the shoe fuses will rupture first. Even when the fault does occur upstream of the fuses (and the traditional copper ribbon fuses were not exactly reliable), there is still a possibility that the substation will not recognise it as a fault, simply a very high current, especially if the failure occurs some distance away from the substation(s). Discriminating reliably between full load current and a distant fault current is a tricky business, for which there protection devices that are rather more cunning than a simple electro-magnetic trip.

 

Jim

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5 minutes ago, iands said:

The lamps in the egg box are wired in parallel. If one lamp fails, the remainder show a bit brighter. 

I'm not convinced. If they were all wired in parallel, there would be 750V across each lamp and 750V lamps are not exactly common; if one failed, the voltage, and therefore current, through the others would remain exactly the same, only the total current would be 5/6 of what it had been.

 

If the lamps are wired as two parallel strings of three in series, then if one lamp fails, one string will extinguish, but the other will remain illuminated exactly as it was before. The only sort of failure that would cause the lamps to glow more brightly would be if one failed short-circuit, which is a highly unusual occurrence. The Laws of Ohm and others apply just as much on the railway as they do everywhere else.

 

Jim

  • Agree 2

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