As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ELECTRICAL UTILITY BUSS PROBLEM. LT AND RT UTILITY BUSS TRIPPED ABOUT 20 MINUTES OUT. UNABLE TO RESET AND THE AIRCRAFT RETURNED TO IAD. RELAYS K148 (SYS 1 AIR/GND) AND K10109 (UTIL/GALLEY PWR FLT RESET) WERE REPLACED AS A PRECAUTION. M116 BUSS POWER CONTROL UNIT (BPCU) ALSO REPLACED. THE DIRECT CAUSE OF THEN ANOMALY IS UNKNOWN; HOWEVER, IT HAS NOT RECURRED SINCE REPLACEMENT OF COMPONENTS.