A system includes a transformer rectifier unit (TRU) (110) including a backfeed sense module (202). A contactor (114) is operatively connected to the TRU for selectively supplying DC power to a DC bus (112) from the TRU with the contactor closed and isolating the DC bus from the TRU with the contactor opened. A contactor driver (226) is operatively connected to receive a signal from the backfeed sense module and to control opening and closing of the contactor based on the signal. The contactor driver is configured to open the contactor upon receipt of the signal indicative of backfeed detected in the TRU.