Comparison of safety between overhead line vs third rail electrification systems

SpacePhoenix · 28 Jun 2017

XDM said:
Sadly another statistic showing 25kv is more of a killer than the much vilified but simple third rail. Very few survive 25 kv contact or even being within centimetres of the line, 750v dc is often survivable, but do not try it. And third rail is so much cheaper & less disruptive to instal & perfect for passenger trains up to 100 mph.

3rd rail has a much greater chance of someone accidentally coming into contact with it. With overhead, unless there has been some structural failure bring the wires near to someone you'd have to climb a structure like the support mast or climb onto the top of a train to come close enough to get electrocuted

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Juniper Driver · 28 Jun 2017

SpacePhoenix said:
3rd rail has a much greater chance of someone accidentally coming into contact with it. With overhead, unless there has been some structural failure bring the wires near to someone you'd have to climb a structure like the support mast or climb onto the top of a train to come close enough to get electrocuted

This is one reason why they are moving away from installing more third rail and instead are installing 25kv instead. Actually AFAIK overheads are cheaper to run. More power effective?

LowLevel · 28 Jun 2017

25kv will leave you alone unless you interfere with it, as will 3rd rail. It's far easier however to interfere with 3rd rail at ground level and while it may or may not kill you it will still do awful things to your insides at the same time.

rebmcr · 28 Jun 2017

Juniper Driver said:
This is one reason why they are moving away from installing more third rail and instead are installing 25kv instead. Actually AFAIK overheads are cheaper to run. More power effective?

Yes, yes, and yes.

al78 · 28 Jun 2017

Juniper Driver said:
This is one reason why they are moving away from installing more third rail and instead are installing 25kv instead. Actually AFAIK overheads are cheaper to run. More power effective?

More vulnerable to windstorms?

Camden · 28 Jun 2017

SpacePhoenix said:
3rd rail has a much greater chance of someone accidentally coming into contact with it.

And yet, time after time, the stories in the news are about people being electrocuted by OHLE, not the third rail...

Based on the facts on the ground, your theory seems to be up in the air.

najaB · 28 Jun 2017

Camden said:
And yet, time after time, the stories in the news are about people being electrocuted by OHLE, not the third rail...

Most likely for the same reason that we read more about deaths due to heart attacks than morbidity associated with diabetes, despite the latter being the cause ofmore suffering and a greater drain on NHS resources.

"Man suffers permanent paralysis of leg" doesn't sell as many papers as "Boy killed in rail depot" despite the former happening more often than the latter.

TheEdge · 28 Jun 2017

Camden said:
And yet, time after time, the stories in the news are about people being electrocuted by OHLE, not the third rail...

Based on the facts on the ground, your theory seems to be up in the air.

Because its quite possible to "walk away" from a third rail shock, which means no news story for some idiot in hospital. 25kV will almost always cook anyone who comes in contact with it, and thats a news story when a kid gets killed.

But as najaB says that's irrelevent. Stay off the bloody railway.

TractiveEffort · 28 Jun 2017

HLE said:
Horrible to read. Just shows that the railway will never be a playground and why. Feel for the family.

Wish they'd also teach people, particuarly journalists that high voltage alone isn't dangerous - if the 25kv OLE only had a few mA as the current, then it wouldn't harm you in the slightest. Unless the physics lectures back in the day were wrong...

Anyone know the power output for both DC and AC electrification? Or what the current level is. Rather than simply using voltage as a gauge of which one is safer - although personally I wouldn't go near either as it's prettt obvious the current and therefore the power output will be a lot higher than what my organs can stand!!

25KV OHL current draw potential is for all intents and purposes, unlimited, 750dc current draw is max 64kA for 20ms.

najaB · 28 Jun 2017

TractiveEffort said:
25KV OHL current draw potential is for all intents and purposes, unlimited...

I'm not 100% convinced that is the case. If it was then grounding the OHLE when it's switched off for maintenance would produce some long lasting pretty fireworks if it was accidentally re-energised.

GB · 29 Jun 2017

XDM said:
Sadly another statistic showing 25kv is more of a killer than the much vilified but simple third rail. Very few survive 25 kv contact or even being within centimetres of the line, 750v dc is often survivable, but do not try it. And third rail is so much cheaper & less disruptive to instal & perfect for passenger trains up to 100 mph.

No system is perfect, and that includes third rail.

Juniper Driver · 29 Jun 2017

al78 said:
More vulnerable to windstorms?

Happens but we've been running overheads since the year dot.Other circumstances bring the wires down.(also)

Think they could get them up faster than third rail but I'm no expert on this and I guess it depends on circumstances also.

I've worked with overheads and I think I prefer these to third rail.

SpacePhoenix · 29 Jun 2017

For both AC and DC to they use rail shorting bars (for AC whatever the equivalent is) at each end of a engineering possession to guard against the power accidentally being switched back on?

al78 · 29 Jun 2017

Juniper Driver said:
Happens but we've been running overheads since the year dot.Other circumstances bring the wires down.(also)

Think they could get them up faster than third rail but I'm no expert on this and I guess it depends on circumstances also.

I've worked with overheads and I think I prefer these to third rail.

Out of interest, during high winds, is it the wind itself that damages the OHL or is it airbourne debris or trees coming down that cause most damage?

Juniper Driver · 29 Jun 2017

al78 said:
Out of interest, during high winds, is it the wind itself that damages the OHL or is it airbourne debris or trees coming down that cause most damage?

I can only say that I'm no expert on this as I have been on third rail territory for nearly 29 years and OHLE almost seven years...I do remember the 1987 storm which had the wires down and they were using class 47 locos and MK 1 stock on locals but there are other factors bring the wires down to which i don't really want to go into.

To your question I would guess trees would damage the overhead wires.

SpacePhoenix · 29 Jun 2017

What current does DC typically run at? I remember that Mythbusters done a myth on peeing on the 3rd rail, can't remember if they deemed to to be lethal, but the current they were using is probably a fair bit less then whatever DC runs at

A Challenge · 29 Jun 2017

SpacePhoenix said:
What current does DC typically run at? I remember that Mythbusters done a myth on peeing on the 3rd rail, can't remember if they deemed to to be lethal, but the current they were using is probably a fair bit less then whatever DC runs at

Interestingly it doesn't say on the Third Rail Wikipedia article!

najaB · 29 Jun 2017

SpacePhoenix said:
What current does DC typically run at?

A fully loaded EMU can pull 2000A easily.

bb21 · 29 Jun 2017

Camden said:
And yet, time after time, the stories in the news are about people being electrocuted by OHLE, not the third rail...

Based on the facts on the ground, your theory seems to be up in the air.

Incidents don't always get reported in the papers.

I have one from this week when a teenager got electrocuted at Sunningdale. She did survive although was in a very bad shape. Last year a graffiti artist was fatally electrocuted at Bournemouth.

Plenty of trespass incidents in third rail land, and every single one runs a very high risk of electrocution.

Paul180 · 29 Jun 2017

SpacePhoenix said:
What current does DC typically run at? I remember that Mythbusters done a myth on peeing on the 3rd rail, can't remember if they deemed to to be lethal, but the current they were using is probably a fair bit less then whatever DC runs at

Personally I take some of what the Mythbusters do with a pinch of salt.

Like peeing on the 3rd rail to start with!

Anyway I will let people make their own conclusions If after watching this video you think it is ok your more than welcome to try it personally I won't be because I know what the outcome would be.

https://www.discovery.com/tv-shows/mythbusters/videos/peeing-on-third-rail-minimyth

cjmillsnun · 30 Jun 2017

XDM said:
Sadly another statistic showing 25kv is more of a killer than the much vilified but simple third rail. Very few survive 25 kv contact or even being within centimetres of the line, 750v dc is often survivable, but do not try it. And third rail is so much cheaper & less disruptive to instal & perfect for passenger trains up to 100 mph.

Twaddle.

With both systems, if you come into contact with them (ie complete a circuit), more often than not there is one outcome.

SpacePhoenix · 30 Jun 2017

Is it AC or DC where the current makes the muscles contract and so making someone grip the cable or rail even tighter?

SPADTrap · 30 Jun 2017

SpacePhoenix said:
Is it AC or DC where the current makes the muscles contract and so making someone grip the cable or rail even tighter?

That's DC.

Smudger105e · 1 Jul 2017

XDM said:
And third rail is so much cheaper & less disruptive to install & perfect for passenger trains up to 100 mph.

I was always told that because 3rd rail needs a substation every 3 miles, it is actually more expensive to install than 25Kv overhead. I also read that 3rd rail is better at higher speeds than overhead because contact is easier to maintain.

And it is not as lethal as you might think, I have had 7 or 8 750v belts in my time. But fall on it and you are in big trouble. No second chances with 25Kv.

I am in no way suggesting that anyone tries touching 750v.

And mills is what kills, that's why RCD breakers are set to trip at 30mA,

AM9 · 1 Jul 2017

Smudger105e said:
I was always told that because 3rd rail needs a substation every 3 miles, it is actually more expensive to install than 25Kv overhead.

It can be depending on the needs of traffic using it, (e.g. density, gradients, train length/weight, no. of stops and speed).

Smudger105e said:
I also read that 3rd rail is better at higher speeds than overhead because contact is easier to maintain.

Quite the opposite, third rail falls down and maintenance costs rise as speeds approach 100mph, which is a common mainline speed these days. OLE is good for speeds over 200mph, - see HS1 and high speeds across the world.

Smudger105e said:
And it is not as lethal as you might think, I have had 7 or 8 750v belts in my time. But fall on it and you are in big trouble. No second chances with 25Kv.

Just because you may have had shocks from a nominal 750VDC conductor, it doesn't mean that much current flowed through your body, especially if you were wearing shoes and the environment was dry. 25Kv however is safe almost all the time except to those who are tall enough to reach a 4.5m high cable. People that tall should know better.

XDM · 28 Jun 2017

Split from Boy (11) dies after sustaining 'serious electrical burns' at rail depot

Sadly another statistic showing 25kv is more of a killer than the much vilified but simple third rail. Very few survive 25 kv contact or even being within centimetres of the line, 750v dc is often survivable, but do not try it. And third rail is so much cheaper & less disruptive to instal & perfect for passenger trains up to 100 mph.

HLE · 28 Jun 2017

Anyone know the power output for both DC and AC electrification? Or what the current level is. Rather than simply using voltage as a gauge of which one is safer - although personally I wouldn't go near either as it's pretty obvious the current and therefore the power output will be a lot higher than what my organs can stand!!

thecrofter · 2 Jul 2017

najaB said:
I'm not 100% convinced that is the case. If it was then grounding the OHLE when it's switched off for maintenance would produce some long lasting pretty fireworks if it was accidentally re-energised.

Generally the U.K. 25 kV system is limited to a maximum fault current of 6 kA. Apart from where Auto-Transformer systems have been installed that have (or plan to be) uprated to 12 kA.

HSTEd · 2 Jul 2017

I claim Fair Dealing on the following for educational and research reasons:

I made an FoI request for documentation from "Electrical Power Asset Policy Section 2 - Historical Analysis".
Total risk for third rail according to Network Rail's own analysis is roughly 8 Fatality Weighted Injuries on third rail, and 1 FWI for 25kV systems.

Roughly 1620km of third rail electrification route, 3250km of 25kV electrification route.
Which makes:
0.000308 FWI/km-year for 25kV electrification
0.004938 FWI/km-year for third rail electrification

So about 0.0046 FWI/km-year excess deaths on third rail electrification.
The value of prevented fatalty is something on order of £1.6m - whch means the excess safety costs of third rail electrification is ~£7,360/ route km-year

£7360/route km-year sounds like a lot
But at current costs of 25kV electrification it is effectively negligible.

swrailuser · 2 Jul 2017

max speed on third rail 110 if your lucky

OHLE 325 KM in europe 140 mph here

transformer 3rd rail 1 per mile

ole 5 miles or more

economics power transfer and speed

Comparison of safety between overhead line vs third rail electrification systems

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