GND PWR UNIT CONNECTED TO ACFT WITHOUT FLC KNOWLEDGE. NO MARSHALLER FOR START AND TAXI OUT. ACFT HIT GND PWR UNIT WITH L PROP WHEN STARTING TAXI.

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I WAS THE PIC OF FLT FROM CMH TO PIT. I REMAINED IN THE COCKPIT OF THE ACFT FROM THE TIME OF OUR ARR UNTIL THE INCIDENT. AT NO TIME WHILE WE WERE ON THE GND DID ANYONE ADVISE ME THAT GND PWR HAD BEEN CONNECTED TO THE ACFT. ONCE THE PREDEP PAPERWORK WAS COMPLETED AND THE APPROPRIATE CHKLISTS WERE COMPLETED; THE ENGS WERE CLRED AND STARTED. WE RECEIVED TAXI INSTRUCTIONS FROM ATC. MOMENTS AFTER THE TAXI COMMENCED; IT BECAME EVIDENT THAT AN EXTERNAL PWR RECTIFIER WAS STILL ATTACHED TO THE ACFT. I INITIATED AN IMMEDIATE SHUTDOWN OF THE ACFT AND ORDERED THE DEPLANING OF ALL PAX. SUPPLEMENTAL INFO FROM ACN 323647: I RETURNED TO THE ACFT AND PERFORMED A PREFLT WALKAROUND; WHICH DID NOT REVEAL THE PRESENCE OF A PWR CART. I WENT INSIDE THE CABIN TO COLLECT ANY CARRY-ONS THAT WOULD NOT FIT UNDER THE SEATS. I THEN TOOK MY SEAT AND THE CAPT SAID THAT THE LUGGAGE HANDLER LEFT AND CALLED FOR THE BEFORE START ENG CHKS. I RECEIVED CLRNC FROM ATC TO TAXI AND JUST AS WE MOVED FORWARD THERE WAS A LOUD BANG AND VIBRATION. IT WAS APPARENT WE HIT SOMETHING WITH THE PROP. THE CAPT SAID 'WHAT WAS THAT' AND I SAID 'FEATHER THE ENGS.' HE FEATHERED THE L ENG AND I FEATHERED THE R ENG. THE PAX WERE DEPLANED AND NO ONE PANICKED OR WAS INJURED. AFTER EVERYONE WAS SAFELY INSIDE IT WAS APPARENT THAT WE HAD HIT THE PWR CART. THE PWR CART WAS IN A BLIND SPOT ON THE CAPT'S SIDE OF THE ACFT. IF THE ACFT WAS CHOCKED AND A GND MARSHALLER WAS PRESENT THIS MAY NOT HAVE OCCURRED.