If Sensor racks are not mounted on a wall, there are keyholes on the rear of the rack which need to be covered. If these holes are left exposed, one could reach in and contact the bus bars.
There is a kit to cover these holes. The kit contains (3) plates and (6) screws. The P/N for the kit is 7051K1001. (there are not any in stock ETC may be able to build them up.)