Abstract: An automatic transfer switch for automatically switching an electrical load between two power sources that includes a switch module containing circuitry for facilitating the switching function, and having two attached input cables and one attached output receptacle. The switch module may be mounted directly on or adjacent to the back of a piece of rack-mounted equipment, thereby minimizing the probability of a power failure between the switch and the equipment. The switch is relatively small, requires no mounting space within a rack, and requires minimal cord lengths.