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Here is one very lucky man....he was inches away from the live rail !
Here is one very lucky man....he was inches away from the live rail !
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Underground trains operate at 630 volts DC (750 volts on National Rail track). The positive rail (mounted outside the running rails, the rail furthest from the platform at stations) is at a potential of 420 volts above earth and the negative rail (mounted centrally between the two running rails) at 210 volts below earth. http://
At tube stations, there is a pit between the running rails so space around the negative rail.
At tube stations, there is a pit between the running rails so space around the negative rail.
Sorry, Jonathan. I don't understand any of that. :-(
It means that the current for the trains’ traction motors are supplied by current running through both the outside rail and the centre rail.
On the “third rail” system, widespread on the old BR Southern Region, the trains are powered at 750v DC. This is supplied at +750v via the Third rail (outside the running rails) and the return to complete the circuit is via the wheels of the train, through the running rails and to earth.
On the four rail system used on the London UndergrounD, the current is supplied from the outside rail at +420v but is (in simple but not strictly correct terms) “sucked out” of the traction motors by being returned to the centre rail, which has a potential of minus 210v. The voltage flowing through the traction motors is thus 630v. Unlike the three rail system, no high voltage current is flowing through earth. This system was adopted because it was thought that stray strong currents flowing through earth may cause electrolytic damage to pipes and cables buried near to the railway tunnels.
The upshot is that touching either of the current rails whilst simultaneously in contact with earth (the running rails being a very good source of earth) will cause electric shock almost certainly leading to electrocution. Being in contact with the outside rail and earth will cause a shock at 420v, whilst contact with the centre rail and earth will impose a shock at 210v. The start prize is received when in contact with the outside rail and the centre rail. This will impart a shock at 630v.
It means that the current for the trains’ traction motors are supplied by current running through both the outside rail and the centre rail.
On the “third rail” system, widespread on the old BR Southern Region, the trains are powered at 750v DC. This is supplied at +750v via the Third rail (outside the running rails) and the return to complete the circuit is via the wheels of the train, through the running rails and to earth.
On the four rail system used on the London UndergrounD, the current is supplied from the outside rail at +420v but is (in simple but not strictly correct terms) “sucked out” of the traction motors by being returned to the centre rail, which has a potential of minus 210v. The voltage flowing through the traction motors is thus 630v. Unlike the three rail system, no high voltage current is flowing through earth. This system was adopted because it was thought that stray strong currents flowing through earth may cause electrolytic damage to pipes and cables buried near to the railway tunnels.
The upshot is that touching either of the current rails whilst simultaneously in contact with earth (the running rails being a very good source of earth) will cause electric shock almost certainly leading to electrocution. Being in contact with the outside rail and earth will cause a shock at 420v, whilst contact with the centre rail and earth will impose a shock at 210v. The start prize is received when in contact with the outside rail and the centre rail. This will impart a shock at 630v.
// ... wouldn't having "live rails" be a danger in itself? Over here all electric trains run from overhead power cables. //
Third / fourth rail electrification was installed because it is much cheaper.
But now, in the UK, no new track can be built with live rails. However it would be too expensive to convert existing three / four rail to overhead. The Docklands Light Railway uses a side contact rail where contact with the live surface is unlikely.
Third / fourth rail electrification was installed because it is much cheaper.
But now, in the UK, no new track can be built with live rails. However it would be too expensive to convert existing three / four rail to overhead. The Docklands Light Railway uses a side contact rail where contact with the live surface is unlikely.
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