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Trolley PoleTrolley poles are usually tapered cylindrical poles of wood or metal, used to transfer electricity from a "live" overhead wire to the control and propulsion equipment of a trolley car, tram or trolley bus. This system of current collection was an invention of Frank J. Sprague. Origin of the term The term trolley to describe the pole or the passenger car using the trolley pole is derived from the grooved conductive wheel (trolley or troller) attached to the end of the pole that "trolls" the overhead wire. Modern "trolley cars" usually don't use the trolley wheel at all, but use a grooved sliding "shoe" containing a carbon insert. Description of the device The trolley pole sits atop a sprung base on the roof of the trolley vehicle, the springs maintaining the tension to keep the trolley wheel or shoe in contact with the wire. If the pole is made of wood, a cable brings the electrical current down to the vehicle. A metal pole may use such a cable, or may itself be electrically "live," requiring the base to be insulated from the vehicle body. Trolley poles are usually raised and lowered manually by a rope from the back of the vehicle. The rope feeds into a spring reel mechanism, called a trolley catcher. The trolley catcher contains a detent, like that in an automotive shoulder safety belt, which "catches" the rope to prevent the trolley pole from flying upward if the pole is dewired. Single and double pole usage When used on a trolley car or tram, i.e., a railway vehicle, a single trolley pole collects current from the overhead wire, and the steel rails on the tracks act as the electrical return. Trolleybuses, on the other hand, must use two trolley poles and dual overhead wires, one pole and wire for the negative "live" current, the other for the positive or neutral return. Decline in usage Trolley poles are still common on trolley buses, but on railway vehicles using overhead wire, the trolley pole has usually given way to the bow collector or the pantograph, a folding construction of metal that presses a wide contact pan against the overhead wire. While more complex than the trolley pole, the pantograph has the advantage of being almost free from dewiring, being more stable at high speed, and being easier to raise and lower automatically.
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