What was found
REAC BUS CB POPPED. FOLLOWED BY ALERTS FROM ITEMS PWRD BY BUS. IRU 2, ATC XPDR 2, GPWS FAULT, IRU ON BAT, PITOT HEAT, FO SEL FADEC ALT, RESET CB AND SYSTEM CAME BACK. CB POPPED AGAIN 1 HOUR LATER. CONTINUED WITH DEGRADED SYSTEMS TO KORD. REMOVED ALL POWER FROM AIRCRAFT FOR 20 MINUTES AND REMOVED R EMERGENCY AC BUS SENSING RELAY R2-5157. REINSTALLED RELAY AND POWERED AIRCRAFT PER 20-20-03 AND 20-00-09. ALL LATCHED FAULTS CLEARED AND ALL EPCU RETURN TO SERVICE AND OPERATIONAL TESTS NORMAL. OK FOR SERVICE.