CENTUM

The electricity flows through the coil of the motor(s) and eventually is grounded via the body of the locomotive and the wheels into the train tracks

A train gets the needed electricity from the overhead cables which allows it to function. The current then passes through the metallic body of the train into the rails through which it passes to the ground leading to the completion of the circuit.

(Reference: https://www.thehindu.com/sci-tech/electric-train/article2029223.ece#:~:text=The%20electrical%20circuit%20is%20completed,then%20connected%20to%20the%20rails.)

The current flows through the body of the train and then seeps into the ground via the tracks, exiting the train. Hence, the circuit is completed.