The COM-72 frame used a pair of PS-72 plug in PSU modules.  The main and redundant power-supply modules, with separate AC inputs, come standard with the Compact 72. Changeover between power supplies is completely transparent to the system, for fail-safe operation. The unit has both an audible failure alarm and failure relay contacts to activate a remote signal. An over-temperature sensor is connected to both an audible alarm and a warning LED, allowing the system operator to diagnose and correct any power anomalies while the system remains operational.