AN MD88 WHILE PERFORMING THE PREFLT CHK THE FO NOTED THE OPEN #3 COM TRANSCEIVER CIRCUIT BREAKER AND RESET THE BREAKER UNAWARE THE ANTENNA WAS BEING REPLACED. THE CIRCUIT BREAKER WAS NOT TAGGED OR PLACARDED.

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APCHED ACFT COCKPIT FOR PREFLT. NOTICED THE USUAL: NO 'ACFT OUT OF SVC' TAG ON THROTTLES; LOGBOOK CHKS GOOD; FLUIDS GOOD; OXYGEN MASKS GOOD; ETC. RESET THE RED CIRCUIT BREAKER THAT WE ROUTINELY PULL ON EVERY ARR. HOWEVER; I NOTICED THE VHF COM #3 CIRCUIT BREAKER POPPED. I ADVISED THE CAPT I WAS GOING TO RESET IT. HE AGREED. I GOT MY UMBRELLA AND DID MY WALKAROUND. UPON MY RETURN; I FOUND 2 MECHS IN THE JETWAY MAKING AN ENTRY IN THE LOGBOOK. I HEARD ONE SAY 'I WONDER OF THE SELCAL IS WORKING?' I TOLD THEM I HAD RESET THE VHF COM #3 CIRCUIT BREAKER. (VHF COM #3 PWRS ACARS; OUR NORMAL SELCAL COM.) ONE MECH TURNED TO ME AND SAID 'GREAT...I WAS CHANGING THE #3 ANTENNA...I COULD HAVE BEEN ELECTROCUTED.' I SMILED AND WENT INTO THE COCKPIT; ASSUMING HE WAS JOKING WITH ME. LATER; THEY HANDED ME THE LOGBOOK; AND SURE ENOUGH; THERE WAS AN ENTRY FOR VHF COM #3 ANTENNA CHANGE. I IMMEDIATELY TOLD THE CAPT THE STORY. AFTER THE TRIP; I RPTED THE EVENT TO OUR COMPANY'S SAFETY HOTLINE. USUALLY MAINT ARE CONSERVATIVE AND PUT THE 'ACFT OTS' TAG UP EVEN FOR THE LITTLE THINGS. WE PLTS TRULY HONOR THE 'WARNING' THE TAG IMPLIES -- IN FACT; WE NORMALLY DROP OUR BAGS IN THE JETWAY AND ASK MAINT TO CALL US WHEN THEY'RE DONE. WE DON'T EVEN ENTER THE FLT DECK.