*Back for the components in a fixed network cabinets, compare common arrangement is  PLC + power relay fuse + terminal; These devices will be arranged on the back, so that when they work in transportation and more stable, at the same time, also facilitate wiring.*Fixed when need drill hole on the back, PLC/power can be directly to the backplane, other basic is first fixed guide rail on the back, then your card on the device onto the guide rail.