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will you get electrocuted widdling on the middle rail??

Wess said:
BTW..Voltage has little to do with it..it is the Amperage that kills you.
You can with stand high Voltages but not high amperage.

good Greif. AC or DC has nothing to do with whether you get pulled toward it or not. It's the muscle contraction.
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The bodies resistance is fairly constant so the current through it is directly proportional to the voltage. The higher the voltage the more current.


If you touch a DC supply the muscles will contract and stay contracted until the circuit is broken. With an AC supply the circuit is effectively broken 50 times a second with a 50Hz supply so there is more chance of being able to let go of the live supply.

Firemen use the back of their hands when searching smoke filled buildings so that if they do touch a live wire the fingers will bend away from the cable rather than clamping onto it.
 
If you touch a DC supply the muscles will contract and stay contracted until the circuit is broken. With an AC supply the circuit is effectively broken 50 times a second with a 50Hz supply so there is more chance of being able to let go of the live supply.
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I know .... Why are you telling me? Tell the poster above and perhaps focus more on the myths written in this thread?
Rather than trying to impress your knowledge on people that already know?

The previous poster somehow thinks (the way I read it) that with AC and Dc one attracts and one doesn't. (yet another urban myth)
 
Velouria said:
No... it's 630 in total and 200ish volts negative on one rail, and 400ish positive on the other. This is for bizarre electrical reasons... It was something along the lines of, if they had only a third rail and put 630 volts DC through it, you could get electrolysis effects and that could cause bits of the tube (wires, points, tripcock stops, etc) to stop working as they slowly dissolved away :D.
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Ah here it is. Seems the concerns were more abt other infrastructure rather than the Tube's infrastructure...
 
Wess said:
I know .... Why are you telling me? Tell the poster above and perhaps focus more on the myths written in this thread?
Rather than trying to impress your knowledge on people that already know?

The previous poster somehow thinks (the way I read it) that with AC and Dc one attracts and one doesn't. (yet another urban myth)
Click to expand...

Only the first part was aimed at you.

The bit you quoted was a general comment. :p
 
noodles said:
I wondered when someone would realise that the crucial bit is the current not the voltage.
Click to expand...

Ahem.

Me said:
The bodies resistance is fairly constant so the current through it is directly proportional to the voltage. The higher the voltage the more current.
Click to expand...
 
In stations the positive rail is always the one furthest from the platform, the one in the middle is the negative rail. Apparently it's to cut down on fatalities :confused: but I don't see that being zapped by 210v is an awful lot better than 420v

But hey, what do I know? I just drive the fuckers.
 
Oxpecker said:
I don't see that being zapped by 210v is an awful lot better than 420v
Click to expand...

Stupid or drunk-but-not-falling-over person steps down to pick up their dropped mobile (or the 1906 equivalent - a telegram they were reading?)

Not having 410V right there will save a few lives. Whether they deserve to be saved is another matter :)
 
Poi E said:
Live rails on trains are such a cheap-arse measure. I believe that in the EU train companies can no longer build new live rail lines. They must be overhead (as they used to be in the UK before the country went broke fighting wars.)
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is there a European Comission rule about that?
 
No idea where the rule comes from.

Nor exactly what it is. If National Rail decided to electrify, say, the Ashford-Hastings line it'd be daft to have an isolated stretch of overhead surrounded by third-rail... and whatever the rule is, they'd get an exception.

But they're building new metros all over Europe, with third rails. Some of them are upside-down third rails with insulating covers. But not all... so how's that work?
 
Not "absolute". I remember there being some rule - and for example I'd be very surprised if they got permission to put in 3rd rail Marylebone-Birmingham even if they wanted to. But it's far from clear what the rule is.
 
Poi E said:
Live rails on trains are such a cheap-arse measure. I believe that in the EU train companies can no longer build new live rail lines. They must be overhead (as they used to be in the UK before the country went broke fighting wars.)
Click to expand...

That's not actually true. The Southern Railway started using third-rail electrification in the 1930s, as a means of replacing steam-hauled suburban trains. After the war, AFAIK they did consider replacing third-rail electrification with catenary wiring, but decided against it on grounds of cost, so we're still stuck with it. But every other electrification project has used overhead catenaries.
 
3d rail aint dead - though limited in expansion terms now.

It makes sense as an add on to existing schemes - some coniideration is n being given to Bidston - Wrexham as an add on to the Merseyside system - Watford Jct - Croxley - Met line would also be 4th rail if its ever done. The economics of overhead versus 3d rail are important thought - u need a lot more substations and track sectioning cabins for DC compard to AC overhead.

Crewe - Kidsgrove in 2003 took no extra feeder stations at all - a great help in flexible routing for West Coast. We need to do more -
 
wiskey said:
do you get electrocuted if you piss on the middle rail of the tube line??

it carries a 210v DC current.

:confused:

edited to say its 630v
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OK, it's not quite as simple as that...

On surface 3rd rail systems, they use the running lines, regularly tied to earth, as the return for the traction supply. When they tried that on the Tube, the traction current return used to cause electrolytic corrosion of the (cast iron) tunnel liner, so the solution was to put in a 4th rail, which is the one between the tracks.

For some reason which escapes me, they keep this at a potential of a couple of hundred volts the other side of earth from the "live" supply.

So, if you piss on the middle rail and you get a shock, it'll be a smaller shock and at a lower potential than if you go for the live rail.

But I have no idea whether you'd get a shock, and I have no plans to conduct any tests (mainly because I'm about 200 miles away from the nearest Tube line and even I can't piss that far)
 
wiskey said:
do you get electrocuted if you piss on the middle rail of the tube line??

it carries a 210v DC current.

:confused:

edited to say its 630v
Click to expand...

I recall that I escaped scot-free pissing (while pissed) on some kind of substation a few years ago in Bristol :)

I think I was lucky :)
 
What is the benefit of overhead vs 3rd rail systems (other then in saving a few idiots running across the track)

From what I can see overhead powerlines are complicated, prone to failure, expensive to install and maintain and hideously ugly.

Please tell me there is something other then saving the stupid from themselves that leads us to use overhead. More capacity or something?

I am purely a layman so please excuse this post if I'm missing something glaringly obvious.
 
suzee blue cheese said:
Track maintenance workers?
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Possibly, but I suspect the procedures already in place establish a protocol for working with live rails, otherwise we'd be awash with dead rail workers in the SE. THe poor sods are out there rain or shine every day.

Third rail systems are a nightmare at complex track interchanges. I've been travelling on both mainline pendolino (sp?) and suburban rail this last week, and the power rail setup at some of the points interchanges on suburban rail would make your eyes bleed. Spaghetti junction has nothing on them.

However I suspect it's mainly an electrical thang.. Voltages are kept low due to the lack of clearance between the third rail and the ground. This means you need more sub-stations to power the system, making it more expensive. Also, due to the lower voltages, you have less power available for the train engines unless you increase the current, which brings a fresh set of problems.

Does the "leaves on the track" crap apply to power tracks too ? I suppose just because the leaf layer is enough to reduce friction on the traction, it doesn't necessarily lead to a reduction in conductivity but it might be another reason.
 
Radar said:
Does the "leaves on the track" crap apply to power tracks too ? I suppose just because the leaf layer is enough to reduce friction on the traction, it doesn't necessarily lead to a reduction in conductivity but it might be another reason.
Click to expand...

I don't think so. We all get training on scraping the ice of the third and fourth rails because that seriously reduces conductivity and often causes stalled trains. The leaves only cause a problem when they've been reduced to an almost invisible layer of slime by the pressure of metal wheels on metal running rails; there isn't that sort of contact between traction shoes and the juice rails.

Of course, ice forming on overhead cables brings its very own set of problems.
 
Radar said:
Third rail systems are a nightmare at complex track interchanges. I've been travelling on both mainline pendolino (sp?) and suburban rail this last week, and the power rail setup at some of the points interchanges on suburban rail would make your eyes bleed. Spaghetti junction has nothing on them.
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Not as bad as 4 rail systems ;)

Crossover%20at%20Ealing%20Bdy.JPG
 
Velouria said:
Not as bad as 4 rail systems ;)
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True, lots more opportunities for things to snag :(

Must be a pig if you get gapped in the guts of a series of those buggers :(

I wonder, in the tube's case would they try and use jump leads to get out of it (with all the dangers to the driver that would entail) or do they sit there until someone pushes them onto a live conductor ?
 
Certainly is - with the very rarely used connection to the Central line visible ..

Re gap jumpers - still in use I believe.

Now if you want a scary job - as I did once - ice scraping the juice rail on the District line outside Wimbledon after a gapped train stalled (tripped by frozen snow can you imagine) - in blowing snow and in the dark. I was younger then and keen to keep things moving - Winter 1987 -

On the same night cleared the points (after we fouund them in a snow drift) - at Motspur Park - it was so cold I felt I was in Tolstoys Anna Karenina - minus the suicide.....

And as for the deicer train stalled on the Wall of Death ....
 
The Wall of Death is the Wimbledon - Sutton line via St Helier.

It was built in the 1930s for electric trains - has steep gradients - circa 1 in 37 - and the service was Holborn Vdct - Sutton via Tulse Hill and West Croydon and back via St Helier - Wimbledon - Streatham - H Viaduct ----- in other words a circle line.

Coined by the drivers due to the similarities to the one time fairground stunt and its "back to where you came from" .......its now Luton to Luton via Streatham and Sutton on Thameslink.

Still an awkward route to run.

Even the dreadnought like de-icing train came to grief on it in the bad weather .... partkly cos there was only a train every 30 mins and its pretty exposed and on fairly high ground.

We gave up on it and waited for the thaw.....
 
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