Single- and Double-pole Usage
When used on a trolley car or tram, i.e., a railway vehicle, a single trolley pole usually 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 positive "live" current, the other for the negative or neutral return. The tramway system in Havana, Cuba also utilised the dual wire system, as did the Cincinnati (Ohio) streetcar system. To reduce electrolytic damage to underground pipes and metallic structures, most tram lines operated with the wire positive with respect to the rails. Toronto's streetcars use a single pole and used since electrification in 1890s, while the city's now defunct trolleybuses used double poles.
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