Three sources are ready to provide power to the load , both relays are energize and one source provide the power . When the 1st source lost the PWR the related relay lost the PWR and the contacts change position to the 2nd PWR source , when the 2nd source lost the PWR the related relay lost the PWR and the contacts change position to the 3th PWR source.
If only one source PWR is available ,that source provide the PWR
The priority sequence of the sources are 1-2-3.
