why do subway trains need only one electrified third rail? I thought electricity needs a negative and positive? shouldn’t we need two electrified rails?

Question

why do subway trains need only one electrified third rail? I thought electricity needs a negative and positive? shouldn’t we need two electrified rails?

In: 2

Answer 1

DC has two wires for negative and positive electricity.

AC has two wires – one has the zap, the other one goes to ‘ground’ or neutral.

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EDIT: Depending on style of train, they either run on DC or AC, although i believe all trains that dont use diesel generators and get electricity from the rails are AC.