Water Heaters - Burnt hot wires top thermostat

Hi all, I have a 10 yr. old 50 gal electrict hot water heater. One of the two original (1988) 30 amp fuses (not breaker)in the disconect was blown 2 days ago. I was not sure why so I replaced it with 15 amp to be a little safer. Tonight I had alittle more time to look in to it. When I pulled the covers off I found both hot wires from upper and lower elements burnt at the contact on the upper thermostat. Both wires are conected to the same contact. The burnt wires were hot enough to melt the stryfome insulation next to the thermostat. I have killed power till tomorrow (no hot showers) but thanks to the person that invented fuses I sill have a house. Does any body have any thoughts as to what could have caused this or what to test for. Thanks in advance for your help.

Just so we will know, you said one of the fuses was blown. This is a double tubular fuse set up, right? It is possible someone installed time delay fuses. There should only be one wire under one screw. Another possibility is the looseness of the connection where the two wires were attached to the one screw incorrectly. Regardless, with the problems you are experiencing, the age of the water heater, you may be in the sunset year of the heater, and need to replace it anyway. That way, you are assured of getting a properly internally wired heater.