serpentine belt keeps popping off

Hi Guys, I have a 92 s-15 jimmy I just replaced the alternator, serpentinr belt, and tensioner on. My problem is that the belt keeps popping off soon as I start the truck. I check the routing and it was good. I do remember reinstalling the alternator with the negative battery conection still on and a spark happened. Could I have damaged the alternator and caused my problem? Please help!

You damaged nothing when you had the spark, as far as the belt goes check all the pullies to see if they trun freely with the twist of a hand, except for the crank of course. while u are at it check all the pullies to see if any of them woble if any of them do that is the problem fix that and u shouldnt have any problem also check and recheck the placement of the belt of all the pullies to make sure that the belt is in the right place when u put it on