A three-position front panel switch chooses automatic operation or may be used to manually select one of the two input sources. When the AUTO mode is selected the AUTO indicator will be illuminated and Input A will be used if it is available. Should Input A fail Input B will be chosen automatically. Indicators show the status of the inputs and which input has been selected.
Each of the twenty-four outputs is monitored for failure either internally or externally. Should one of the outputs fail, a group alarm Fault indicator will illuminate on the front panel. Rear panel input Fault Discrete signals allow external equipment to force the outputs to be derived from either input source in case of a source failure.