What is a flashover? What causes a flashover?
A flashover occurs when the brushes in the commutators of DC traction motors touch each other because of a unusual movement or bump, such as when a locomotive goes over a grade crossing. If the brushes touch each other, an electrical short can occur almost like a lightning strike. Obviously, this can severely damage the traction motors. Locomotives with DC traction motors must have the throttle reduced slightly when going over a grade crossing to reduce the risk of a flashover. Newer locomotives with AC traction motors have no commutator brushes and therefore do not have to be throttled down at grade crossings.
