EMB120 CREW HAS ELECTRICAL FAILURE ON FINAL APCH AND DIVERTS.

Narrative

ON ARR INTO ZZZ ARPT; WE WERE GIVEN AN ILS (DAY; 400 FT OVCST). WE WERE ESTABLISHED ON THE ILS AND FULLY CONFIGURED FOR LNDG; JUST BEFORE ENTERING IFR CONDITIONS WE EXPERIENCED AN ELECTRICAL EMER DC BUS FAILURE; WHICH IN TURN FAILED THE ENTIRE L SIDE OF PANEL IN COCKPIT. ONCE THE COPLT AND I FIGURED OUT WHAT WAS HAPPENING; WE LEVELED OFF FOR A MISSED APCH. IT TOOK AWHILE TO VERIFY ALL FAILURES; SO WENT ON RWY HDG AND CLBED TO 12000 FT. WHILE WE TRIED TO FIGURE OUT WHAT ALL HAD FAILED; WE SQUAWKED 7600 AND IDENT BECAUSE INITIALLY WE HAD THOUGHT WE LOST ALL COMS: NAVS. UPON FURTHER INSPECTION WE HAD ONLY LOST ALL #1 SIDE (#1 COM; #1 AIRSPD INDICATOR; #1 ALTIMETER INDICATOR; #1 VSI; #1 NAV; #1 TUBES; L SIDE ENG GAUGES). WE SPOKE WITHOUT HEADSETS ABOUT THE WX: WHERE TO PROCEED. WE DECIDED TO PROCEED TO A VFR ARPT IN CASE THE #2 SIDE INSTS WERE ERRONEOUS. WE PROCEEDED TOWARDS ZZZ1. WE RAN THE MOST IMPORTANT (EMER) CHKLISTS AND WE THEN SAW #2 COM MAY BE WORKING. THE COPLT TRIED TO REACH SOMEONE (FIRST TIME WAS ONLY STATIC). HE WAS ABLE TO HEAR OUR FLT OPS; WE TOLD THEM WE HAD MULTIPLE FAILURES IN COCKPIT; WE WENT AROUND AND NOW PROCEEDING TO ZZZ1. PLEASE CALL TWR. THEY WERE ON THE PHONE WITH THEM ALREADY. WE THEN ADVISED THEM WE HAD TO SWITCH TO ZZZ1 APCH (WE WERE APPROX 50 MI S OF ZZZ1). WE ADVISED THE FLT ATTENDANT AND PAX THAT WE WOULD DIVERT TO ZZZ1. PLEASE PREPARE CABIN FOR AN EMER LNDG. WE LANDED SAFELY IN ZZZ1 AND WE WERE TOWED OFF THE RWY DUE TO NO STEERING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THAT THE EMER DC BUS #1 HAD SHORTED OUT AND CAUSED OTHER BUSES TO FAIL. THIS BUS IS SUPPOSED TO REMAIN POWERED WHEN ALL OTHERS HAVE FAILED. THIS EMB120 IS A VERY EARLY EXAMPLE WITH A SOMEWHAT UNIQUE ELECTRICAL SYS AND MAY HAVE HAD THIS PROB BEFORE.