Question about the third rail on trains.?

Question

Trains that operate on power from the third rail: My question is, is there a CONSTANT power running through the third rail (meaning all the time) or does the third rail power up a mile or a specified distance before the train goes over the tracks.

My point is, it would be wasteful and dangerous to be powered constantly, instead of when the train is about to go over said tracks. Anyone know the real deal about this? Is it constant power or segmental?

Answer 1

the two rails are (+) and (-). the middle rail is ground.

Answer 2

The tracks are powered constantly. It is not wasteful for, whilst there may be a small amount of earth leakage, electricity is not 'used' until it is 'consumed'. The live rail is only dangerous if some fool goes and touches it. Further, electrification on the third rail system is normal used for high capacity metro operations with trains running fairly closely together. It would probably be more expensive and wasteful to install devices to have a 'rolling' power supply (even if that were possible - I'm no electrical engineer so don't know the answer to that one)

Answer 3

The line is powered all the time. This type of system works best on a rail network like the London suburban, where there is a very intensive train service.

On the London Underground the conductor rails are switched off a night for safety while the maintenance shift are working. They use battery-powered trains which are charged up at the stabling point during the daytime.

Answer 4

On most 3rd-rail-systems the rail is powerd constantly, as others have said before. There is however a tram-system in Bordeaux/France where about 2km of the track (when passing through the most beautiful historic part of the city) is powered by 3rd rail in the street, where only a short section (only underneath the vehicle) is powered.

But this is rather expensive to build and I hear there were lots of problems with the electronic switching in the beginning. Most of the system still uses 'classic' overhead wire.

Answer 5

The third rail is energised at all times, regardless of whether a train is drawing power from it or not. It's not particularly wasteful, the electricity is present but is not being used all the time. It's not dangerous either, as long as you keep away from the tracks.

Track maintenance staff have set procedures to follow when working in electrified areas to ensure their safety; the problem lies with trespassers who have no regard for the law or their own safety by wandering onto the track and getting themselves fried.

Answer 6

The third rail carries current at all times, unless isolated for maintenance work. Yes it is dangerous, because if you touch it the current will pass through your body to ground and you will probably not survive. That is why walking or playing on the tracks is discouraged. Its not wasteful as the current is only used when the engine is moving i.e. driving its motors.

Answer 7

THE POWER IS THERE ALL THE TIME,IT COULDNT WORK ANY OTHER WAY.