I recently go to visit London England.
I had to ride the tube (very enjoyable) just look at he map and you know where to go.
My question— What are all the rails for? I counted 5 and sometimes 6 rails down under.
I asked the staff and they just looked at me as if to say if you do not know then you should not know.
The “third rail” can be on either side of the running rails or between them…sometimes all at the same time. It’s so the shoes maintain constant contact to power as the trains pass over switches and crossovers.
Mark
Some parts of the London Underground Network (Subway) use 4 rails rather than the more common 3 rails. The 4th rail provides a more secure return path for the electric current, in a situation where stray currents and galvanic action can be a problem. Most electrified lines use one or both of the running rails for return current.
Beaulieu has it right. The London underground network has 4 rails throughout. The 3rd rail which runs very close to one of the running rails is the rail used to supply the current to the train. The 4th rail which runs directly down the middle of the running rails is the Negative Return Rail.
Sometimes it can appear there are more than 4 rails due the fact the pick-up rails switch sides in places and can overlap. There can also appear to be more rails in the vicinity of crossovers but if you look carefully you will clearly see it’s a simple 4-rail system throughout.
On many mainline tracks in London the 3rd rail system is used which doesn’t have the central return rail.
From a TV program on the tube I learned that the inner rail is at 200 Volts and the outer rail at 400 Volts (in the other direction) relative to the running rails. Can’t remember which is + and -.
It’s not safe to get in the middle of the tracks if you fall off the platform.
There’s a website about it at http://homepage.ntlworld.com/russelliott/3rd-4th.html
Ok I need to claify my question and observation.
I was on a platform waiting for a train underground or in tube.
There were no intersections just the through trackage.
There were the two running rails 4 ft 8 in apart. Out from the furtherest rail up on insulators about 8 inches is what I presume is the power supply rail.
Inbetween the two running rails were two to three additional rails. They were not clean rail heads. They were mounted and not waiting to be used as replacements.
I could not seen what was close to and below the platform edge.
I was to busy to notice what the track work was at the open elevated platforms.
The location may also have had check rails to keep a derailed train from hitting a platform. One of the middle rails was the return current rail.