Overview
Conduit current collection is a method for supplying electrical energy to street-running vehicles such as electric trams. Instead of an overhead wire, the system locates insulated conductor rails in a narrow channel beneath the roadway; the tram collects electric current through a contact that reaches down into the channel via a slot in the street surface rather than above it with overhead wires.
Design and components
Typical elements include a longitudinal slot in the road surface, twin conductor rails mounted inside the channel, insulation and drainage, and a movable contact mounted under the tram known as a plough, shoe or skate. These contacts are guided along the slot and press against the conductor rails to complete the circuit. The channel must be supported and kept clear of water and debris for reliable operation.
History and development
The conduit system emerged in the late 19th and early 20th centuries as cities electrified their street railways but wanted to avoid overhead wires in central or historic districts. Municipal authorities adopted conduit collection where aesthetics or regulations prohibited poles and wires. Over time the greater cost and complexity of installation and maintenance caused many operators to abandon conduit in favor of overhead wires or other solutions.
Operation, advantages and drawbacks
Advantages: it preserves the visual appearance of streets, reduces risk of overhead wire failures, and confines live conductors below street level. Drawbacks: higher initial construction cost, frequent maintenance to clear the channel, vulnerability to flooding, and more complex switching and trackwork. Modern ground-level power systems offer similar visual benefits with different technical approaches.
Comparison and legacy
Conduit collection differs from third-rail systems (which are generally at track level and fenced off) and from overhead collection (trolley poles or pantographs). While largely replaced in many cities, conduit systems influenced later innovations in discrete or surface-level power supply technology and remain an important chapter in urban transit history.