What was found
THE CREW REPORTED THAT PRIOR TO TOP OF DESCENT THAT A LEVEL 2 ALERT FOR GEN BUSS 3 FAULT WAS DISPLAYED IN THE EAD. FOLLOWED THE QRH PROCEDURES, DEPLOYED THE ADG AND NO FUEL DUMP WAS PERFORMED. LANDED WITHOUT FURTHER INCIDENT OR DELAY. PERFORMED FIM 24-20-17, STEPS 1-5, CHECKED T1-T3 FOR IDG TO GROUND. CHECKED CONNECTIONS P1-8559A & P1-8559B. CHECKED 53-393. GR-3 TO BTR-3, B7-7, B7-8 & B7-9 WITH GROUND = 250 OHMS. CHECKED GENERATOR RELAY & BUSS TIE RELAY. FOUND ALL NORMAL. FOUND RCCB B1-138 DIFFERENTIAL FAULT DEFECTIVE, R & R RCCB AND OPERATIONALLY CHECKED NORMAL.