While the ERM-DA is receiving power it will transmit an occupied telegram every 100 seconds. All linked power controllers will fire there occupied event when they receive the occupied telegram.
When the ERM-DA loses power it will no longer transmit the occupied telegram. Once the linked power controllers no longer receive the occupied telegram from the ERM-DA a timer will count down within the power controller locally. Once the timer expires, the linked power controllers will fire there unoccupied event (provided they were setup to do so).