Third rail only carries 750 volts, whereas Catenary carries 25,000 volts
Underground trains run on third rail, Normal electric trains run on 25,000 volts
The reason they are overhead is quite simple, go within 2 feet of them and you`ll have a hole where the electricity enters your body and a hole where it exits, every part of your body in between that will be burnt to a pulp
Thank you both. The old Southern Railway has managed for 70 ?odd years on third rail ,so it must be reasonably efficient but perhaps not suitable for high speeds? Best wishes,Paul.