In case of a “main power” failure, the “power output” will immediately switch to the “backup EM power”. This will ensure that attached devices at the power output keep operating. During a failure, the alarm contact switches and the status indicator LED (“Main OK”) goes off. Power supplies (main/backup) remain galvanically separated from each other. During normal operation, the alarm contact NO is closed, both power indicators (LEDs) are green and the “power out” is routed from the “main power”. Thanks to the high capacity capacitors mounted on this device, the output power will have a minimal voltage dip during the switchover from “Main power” to “backup EM power”. Please note that if the EM power falls off, and the main power is still in good condition, the alarm contact will be raised after approximately 35 seconds. These devices handle a maximum continuous current of 5 amps at 24v DC. The output power supply is reverse polarity protected  to make sure that devices connected to the power output will not be damaged from reversed power connections. With the onboard potentiometers, the threshold of the power OK can be adjusted. Rotate the potentiometer clockwise to increase the threshold. For main power OK the threshold range is between 18..22v DC, for EM power OK the threshold range is between 15…30v DC.