The present invention discloses a cable tray assembly for a drilling rig or other vertical structure. In one embodiment, an extendable cable tray assembly is provided for retractable attachment to a section of a mast of a drilling rig. The cable tray assembly includes an upper tray connected to the mast in a stationary relationship. A center tray has a pivot end pivotally connected to the mast, and an articulating end rotatable between a stowed position and a deployed position below, and offset to, the upper tray. A lower tray has an upper end and a lower end. The upper end is pivotally connected to the articulating end of the center tray. The lower tray is movable between a stowed position and a deployed position below, and offset to, the center tray. An actuator is provided such that extension and retraction of the actuator results in deployment and retraction of the cable tray assembly.