That said, a ban on third rail seems fair enough, after all it’s an high voltage line running few cm above ground!
I disagree.
That said, a ban on third rail seems fair enough, after all it’s an high voltage line running few cm above ground!
If the trains drag the voltage down then the current through any electric shock would reduce by the same proportion. But it's only about 30% maximum so unlikely to make much difference to the outcome.Isn't it the case that there are a lot of places on the Southern 3rd rail network, mostly those far from substations, where the current is very low because there's so many trains using those sections?
The actual flashover distance is only a few centimetres but understandably standards and procedures require a much greater separation. People standing on platforms may be closer than the latest standards require for new installations, re-design due to meet these standards being one of the reasons for delay and extra cost to recent electrification. However there's never been any case of a 25kV flashover to someone on the ground or a platform as far as I'm aware, except for one where the wires had partly fallen but had not touched the ground which would have cut the supply: http://www.railwaysarchive.co.uk/documents/RAIB_SuttonWeaver2014.pdfIsn't there a considerable risk of arcing from the OLE within a certain proximity, even if you don't come into contact with it.
He had stopped his train having seen damaged overhead power supply wires ahead of it. Following a call to the signaller, he left his train and came close to, or made contact with, an electrically live wire which had broken and was low hanging. The train driver suffered serious injuries. This accident occurred because one of the overhead wires had broken, was hanging down and was electrically live. Two previous trains had come into contact with this hanging wire and consequently tripped the power supply circuit breakers. Each time the circuit breakers had been reset by the Electrical Control Operators in accordance with procedures to make the overhead wires electrically live again. The driver had left the train to obtain information as to his location to assist in restoring train services as he was trained to do, but did not see the broken wire.
OK, if you are being pedantic, the third rail officially carries 'low voltage'. In power distribution terms, low voltage is in the range 120VDC -1500VDC whereas 25kV is 'medium voltage'. If you touch it the name is irrelevant though - it's dangerous, and the chances of people touching it are infinitely higher than wires at least 4165mm from the rail/crossing road surface. Irrespective of the voltage on the wire being 33 times higher than the 3rd rail. Even if you take the extreme case of the peak voltage at the maximum permissable ac line voltage (29kV), it will be just over 41kV which will still only initiate an arc over a distenace of less than 50mm in air, so at 2.5 metres with a possible 1 metre additional arm reach, the tallest men in the world, (if they were stupid enough) couldn't even deliberately touch the conductor wire.I disagree.
As a rule of thumb, electricity will flashover at a rate of about 1mm per kV in air. Much of the additional clearance is because OLE is not rigid so there are dynamic clearances to maintain.Isn't there a considerable risk of arcing from the OLE within a certain proximity, even if you don't come into contact with it.
The inherent dangers of having lethal voltages at ankle level where even trained staff suffer life-changing or even life-extinguishing injuries may for a while enjoy grandfather rights inherited from a less enlightned age, but to exacerbate the risk by installing more would be unacceptable to the majority of the population.I don't think anyone is denying that third rail is more dangerous than OHLE, it's whether the additional risk means that we can't have any more
After all when I walk down the street there's a risk that a vehicles might leave the road and mount the pavement, but you wouldn't ban cars because of it.
First, the incidents where a person has ignored or defeated the clear protection measures provided, should not be categorised in the same way as accidental events. I don't have actual figures, but I would wager that the true incidents of unintentional contact with high voltage (both 3rd rail and OLE) show OLE to be far safer than 3rd rail. Typically, although a mass evacuation might be classed as trespassing, some causes may ultimately be regarded as likely to provoke one. In those cases, if the automatic removal of 3rd rail power worked, the result would be far more widespread disruption that with OLE where the power is rarely removed. AFAICT, the only case of truly accidental electrocution by OLE has been where a driver has not seen sagging wires that by chance hadn't shorted to ground causing power removal.Having seen all the over-reaction to 3rd rail, here and elsewhere, in recent times, it does seem to me that there have been a number of recent incidents with 25Kv, without an equivalent number of 3rd rail ones. One could almost say that the ORR have got their ban the wrong way round.
Not a first for the ORR, of course.
Well, the user below yours seems to be denying that!I don't think anyone is denying that third rail is more dangerous than OHLE, it's whether the additional risk means that we can't have any more
After all when I walk down the street there's a risk that a vehicles might leave the road and mount the pavement, but you wouldn't ban cars because of it.
Any stats?Having seen all the over-reaction to 3rd rail, here and elsewhere, in recent times, it does seem to me that there have been a number of recent incidents with 25Kv, without an equivalent number of 3rd rail ones. One could almost say that the ORR have got their ban the wrong way round.
Not a first for the ORR, of course.
It isn't just a safety issue. 750VDC is much less energy efficient than 25kV (however the train collects its power). The infrastructure to maintain a usable supply to modern trains is both extensive and inefficient, - and that is with trains deliberately crippled to prevent them drawing full power needed to get the full performance. Thus the route is saddled with lower performing trains and limits that frequently restrict the number of trains working in a locality, (not anything to do with signalling limitations). High current DC (33 times that drawn for an equivalent power on a 25kV ac line) causes many anodic corrosion issues, and requires complex grounding installations at stations where domestic ac supplies are interfaced with remotely supplied traction power.I don't think that third rail is unacceptable to the majority of Londoners, who actually enjoy two live rails(+420V, -210V) rather than one and are having extensions built and proposed.
All that's really wanted in the SR are the Wokingham- Ash and Shalford Jn - Reigate gaps filled. Uckfield is probably a battery job and Ashford could be 25kV (as could Pirbright Jn - Weymouth!).
All movement poses risk - you can only avoid it by avoiding life.
WAO
We all know why not; well, all except those who live in a world of make believe. OLE is massively expensive, we can't afford it and Network Rail have demonstrated that they can't be trusted to deliver an OLE project on schedule at a sensible price. That was the reason MML electrification was cut short.I think that in this case you have a tested and verified system which could replace a (slightly?) more dangerous one. Why not?* . . . . . .
*There sure are reasons why not but I don’t think these are safety related.
Apologies if this has already been said but whether the source is DC or AC, it only takes milliamps to stop a human heart. Given that most household appliances are fused at 13a and I only need 50mA to potentially cause me death, I'm not likely to believe 750 V DC or 25kV AC are any different in terms of risk to life.As a rule of thumb, electricity will flashover at a rate of about 1mm per kV in air. Much of the additional clearance is because OLE is not rigid so there are dynamic clearances to maintain.
AFAICT, the only case of truly accidental electrocution by OLE has been where a driver has not seen sagging wires that by chance hadn't shorted to ground causing power removal.
The point of that post is that I was clarifying the distance that an arc might typically occur. The reason for the safe distance being in metres is to do wioth dynamic changes in the gap (e.g. wind, oscillation from pantograph pressures, etc.), and more relevant to this thread, intrusions into the safety zone. Clearly climbing onto a train roof qualifies for that but there are more subtle risks such as passengers ignoring rules about carrying long objects high above platforms or dangling things over bridges. In those events, the actual arcing zone can be penetrated causing an arc or even direct contact. 750V would need to be as good as touched (i.e. less than 1mm) but the nature of 3rd rail electrification is that such an event is much more likely.Apologies if this has already been said but whether the source is DC or AC, it only takes milliamps to stop a human heart. Given that most household appliances are fused at 13a and I only need 50mA to potentially cause me death, I'm not likely to believe 750 V DC or 25kV AC are any different in terms of risk to life.
When I left school many years ago, I worked in a Telephone Exchange where equipment used 50v however a watch strap or finger ring would have quickly melted if caught on the bus-bars and within the instance of blowing the fuse of significant size. So, the message was, Volts jolt, mills Kill!
Can we just simply agree that the railway is a dangerous place to be.
I like to think I've been more knowledgeable than most about railways all my life, but have never encountered any such rule stated to passengers anywhere.passengers ignoring rules about carrying long objects high above platforms or dangling things over bridges.
We all know why not; well, all except those who live in a world of make believe. OLE is massively expensive, we can't afford it and Network Rail have demonstrated that they can't be trusted to deliver an OLE project on schedule at a sensible price. That was the reason MML electrification was cut short.
Third rail, and on London Underground third and fourth rail, is used by literally millions of people every day. As a Londoner I assure you we don't use it with fearful trepidation. We don't cower and tremble while saying our final prayers. We use it without a moment's thought. The ORR and a handful of rail enthusiasts might froth and splutter about, say, the North Downs Line being giving its long overdue third rail electrification, but people in the Home Counties would be calm and happy.
I've been on a station where there were some children with helium balloons and an announcement was made asking them to keep them under control due to the live wires.I like to think I've been more knowledgeable than most about railways all my life, but have never encountered any such rule stated to passengers anywhere.
It's just about acceptable to discuss safety here, but can we keep cost issues for one of the many other threads that have discussed it already?Should I believe that a 3rd rail full installation is cheaper? Are there any numbers around?
I think the vast majority of urban metro systems round the world select 3rd rail running, including new lines and new systems.
Having seen all the over-reaction to 3rd rail, here and elsewhere, in recent times, it does seem to me that there have been a number of recent incidents with 25Kv, without an equivalent number of 3rd rail ones. One could almost say that the ORR have got their ban the wrong way round.
I’m sorry if someone thinks it isn’t appropriate to have this discussion in this topic. My opinion is that if there’s something dangerous it’s better to talk about it,
We all know why not; well, all except those who live in a world of make believe. OLE is massively expensive, we can't afford it and Network Rail have demonstrated that they can't be trusted to deliver an OLE project on schedule at a sensible price. That was the reason MML electrification was cut short.
Third rail, and on London Underground third and fourth rail, is used by literally millions of people every day. As a Londoner I assure you we don't use it with fearful trepidation. We don't cower and tremble while saying our final prayers. We use it without a moment's thought. The ORR and a handful of rail enthusiasts might froth and splutter about, say, the North Downs Line being giving its long overdue third rail electrification, but people in the Home Counties would be calm and happy.
Assuming "tra" is "tram" then they generally have to use an overhead supply for safety in the street. Limited exceptions are the Alstom APS system which energises sections of the third rail only when the tram is above them, and a few routes that have battery operation over short distances.I’m not sure about that. Most metro systems I see around the world have OLE - often ‘low voltage’ D.C., but the conductors are in the air. Almost every tra system for a start.
Plenty of both historic and modern systems used a conduit system embedded beneath the road surface, such as the streetcars in San Francisco. Such a system would be impractical for heavy-rail use and expensive to install on tramways today, but it does solve the problem of exposed electrical supply.Assuming "tra" is "tram" then they generally have to use an overhead supply for safety in the street. Limited exceptions are the Alstom APS system which energises sections of the third rail only when the tram is above them, and a few routes that have battery operation over short distances.
However many new metros do use third rail, such as those in Saudi Arabia. These are fully segregated either on viaduct or in tunnel, with platform screen doors, so it's extremely difficult to get onto the track bed by accident.
I like to think I've been more knowledgeable than most about railways all my life, but have never encountered any such rule stated to passengers anywhere.
As there has been no large third rail project for decades, it's probable there are no contemporary figures. However in the 1960s while the OLE of the southern half the WCML was costing around £200 million, Woking to Bournemouth was done for about £12 million.Should I believe that a 3rd rail full installation is cheaper? Are there any numbers around?
There are signs on the platforms at Newport station (and, for all I know, elsewhere on the newly electrified GWML) telling passengers not to make contact with the OHE. I can't remember the exact wording, but it includes things like selfie sticks, balloons, etc.