Trolley Pole - Description of The Device

Description of The Device

A trolley pole is not "attached" to the overhead wire. The pole sits atop a sprung base on the roof of the vehicle, with springs providing the pressure 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.

On systems with double-ended railway cars capable of running in both directions, the trolley pole must always be pulled behind the car and not pushed, or dewiring is very likely, which can cause damage to the overhead wires. At terminus points, the conductor must turn the trolley pole around to face the correct direction, pulling it off the wire either with a rope or a pole and walking it around to the other end. In some cases, two trolley poles are provided, one for each direction: in this case it is a matter of raising one and lowering the other. Since the operator could raise the pole at one end whilst the conductor lowered the other, this saved time and was much easier for the conductor. Care must be taken to raise the downed pole first, to eliminate the damage caused by arcing between the pole and wire. In the US, the dual-pole system was the most common arrangement on double-ended vehicles. However, pushing of the pole (called "back-poling" in the US or "spear-poling" in Australia), was quite common where the trams were moving at slow speeds, such as at wye terminals (also known as reversers) and whilst backing into the sheds.

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 or "trolley retriever". 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. The similar looking retriever (see photo) adds a spring mechanism that yanks the pole downward if it should leave the wire, pulling it away from all overhead wire fittings. Catchers are commonly used on trams operating at lower speeds, as in a city, whilst retrievers are used on suburban and interurban lines to limit damage to the overhead at speed.

On some older systems, the poles were raised and lowered using a long pole with a metal hook. Where available, these may have been made of bamboo due to its length, natural straightness and strength, combined with its relative light weight and the fact that it is an insulator. Trolleybuses usually carried one with the vehicle, for use in the event of dewirement, but tram systems usually had them placed along the route at locations where the trolley pole would need reversing.

The poles used on trolleybuses are typically longer than those used on trams, to allow the bus to take fuller advantage of its not being restricted to a fixed path in the street (the rails), by giving a degree of lateral steerability, enabling the trolleybus to board passengers at curbside.

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