The 250V is the limit where the fuse will not arc across itself (ie voltage over 250 V could get by a blown fuse)
Current is current.... a fuse will blow at its amp rating regardless of how much voltage is involved.
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)
1984 Fast/Nicholson 345 "FastForward"