Abstract: A power rail is mounted on the face of storage system support columns. The power from the rail is transmitted to the equipment using a right angle, low clearance power rail trolley. The towing device is mounted to the side of the moving equipment. The device incorporates a new low profile trolley and towing arm attachment to permit mounting inches from the floor surface. The towing device includes a pair of pin engagement guide fingers that provide tolerance for traveling misalignments between the moving equipment and the stationary power rail. When an obstruction is encountered, power to drive the traveling stacker-retriever is cut off. The trolley engagement unit is mounted on a lateral swivel arm, the towing arm. The swivel arm mount has a mechanical overload spring pin detent. If a mechanical overload is detected, the swivel arm disengages from the spring pin detent, causing a limit switch to signal an emergency stop condition to disconnect motive power and to stop the moving equipment.