Abstract: A locking apparatus for electrically isolating a trolley-type electrical connector on the end of a conduit on an electrical mining machine or the like, to prevent an electrical connection from being made with the connector. The locking apparatus comprises an open-ended sheath made from an electrically insulating material, slidably mounted on the end of the conduit, to slide between an extended position in which the sheath surrounds the connector, and a retracted position in which the connector projects through the open end of the sheath. The sheath has aligned openings on opposite sides thereof, adjacent the open end of the sheath. A locking member is adapted to extend through the aligned openings and substantially block the open end of the sheath. A retaining cord tethers the locking member to the sheath. A lock can be used to secure the locking member in its position blocking the open end of the sheath.