Question about London subway and commuter rail

Hello Big Kid

The OUTSIDE third rail provides the 600 VDC (or whatever they use between 600 & 700) for powering the motors, lights and other electric accessories of the train.   The INSIDE (center) third rail is a NEGATIVE rail for RETURN current --- the 2 running rails the wheels run on are not used for return current to the power plant.  The London Underground started their electric operation using that method .

LIONEL TRACK is perfect for modeling London Underground Trains in O Scale --- easy -- just install an outside 3rd rail for appearances and you have your 4-rail track !

Regards - Joe F

They use both systems. If you check the "Four Rail" section here, it explains the reasons for its existence.  https://en.wikipedia.org/wiki/...ectrification_system

@firewood-

Thanks for the link (should of thought of Wiki), it is interesting they used the 4 rail system to keep electrolytic corrosion from  happening,  because of current seep if they used the running rails as the return, never would of thought of that. It is interesting that they get the 630 volts by having +420 on the outside rail and -210 on the center (which confuses the crap out of people who don't understand that voltage is the potential between two surfaces, not an absolute), and that on dual service track they have the running rails wired to the inside third so the running rails are -210, giving the same 630 volts.