Alternator electrical connection burned

The electrial connection from the alternator on my 98 Windstar is all burnt. I can't loosen or tighten the nut for this connection because the bolt thats attached to the alternator keeps turning with the nut (the plastic that holds the bolt in place is all melted). The van still runs but the connection is loose.
I understand that the alternator will have to be replaced, but does any1 know why this could have happened? About 8 months ago the previous alternator had died. The shop that changed it said the connection was burnt too. Can this happen if the connection was not tightened correctly when the alternator was installed?

-Thanks for your help

It could just be that the connection at the alternator has some oxidation/corrosion causing it to heat up due to the resistance. Check if that cable gets hot after some normal run time. Seeing that this has happened twice now :banghead: , I would check that entire cable for any breaks or corrsion that would cause resistance and heat build-up. Clean and inspect the battery cables & connections as well.
G/luck
Joel