If the junction box (connector box) is all sooted up then that's where the fault occurred and for a guess a dead short inside the junction box directly connected live to neutral - there was a very brief flow of much current - great heat and then the external protective fuse blew - as it should.
If it were mine I would clean it up to remove as much soot as possible - give the enclosure and the wiring a very close inspection - concentrate of the bits where you see molten metal.
As long as there's no longer the rogue piece of metal that caused the short and as long as there's no carbon debris from the small explosion then you should be "good to go".
Your fuse sacrificed its life and died to protect the wiring - your pump should have been unaware of it all.
If by some chance the pump has been damaged (I very much doubt it) then you've nothing to lose by assuming it still good and trying it.
I would guess the fault to have been confined to the junction box and to have been caused by a small piece of metal - strand of wire - dropped connector screw or even an untightened screw that worked lose over time shaken by the vibration of the pump.
This is all guesswork...
Good luck...
Peccavi
June 2013
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