posted
Hi there, I have a query and was wondering if you guys could help?
A couple of weeks back i was waiting at a South East London (UK) station when i saw a guy jump down onto the track and walk across the lines.
The thing is the lines use the 'third rail' type system to power the trains by electricity. This guy clearly stood on the electric rail yet did not get electricuted! How so?
I have been told that a 3000v current runs through this tracks so surely the man should have died? Does anyone know how these things work? The only thing i can assume is that the track is only turned on when a train is going over it. Either that or i imagined it all!
Any answers appreciated.
Posts: 1 | Registered: Oct 2005
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posted
The former BR Southern Region current is nominally 750 volts. Probably a little higher if you are near a substation probably less down to about 600 v if you are a goodly distance from a substation and there is a train or two drawing power heavily. It is a direct current system, as are most (all so far as I know) third rail systems. The return side of the circuit is the running rail, except in London Underground where there is a fourth rail between the two running rails for the return circuit.
The rail should be regarded as ALWAYS ON. That is the normal reality. The amperage is huge. That is the reason for the large cross section of the rail. Because the voltage is relatively low, it will not make a long arc, so you have to be very close to it to get shocked. If you touch it and are reasonably well grounded you will be very dead. Trying experimentally to see how close is too close will get you a posthumous Darwin Award.
People that work on these systems do step over these rails, and it can be done safely. However, getting it wrong will be the last mistake you ever make.
So far as I know, the normal range of voltages in the world for third rail systems is between 600 volts and 1000 volts.
George
Posts: 2810 | From: Olive Branch MS | Registered: Nov 2002
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