The APM800 is an MZX addressable power supply monitoring module which is usually used with the PSM800 power supply module to make an addressable power supply.
The APM800 is designed to fix to studs on the top of the PSM800.
The APM800 monitors the PSM800 for mains failure, earth fault, battery charger fault and battery fault. It can reset the PSM800 resettable 24Vd.c. output and initiate a battery test which then reports battery voltage and current to the controller.