When he tried to attach the new front cover it singed the screw and blew the fuse. What could be causing this?
Yep have had exactly that happen!It's not uncommon to have an RCD trip when cutting cable on a properly isolated circuit on a split load board from N-E bridging. If neutral in earth terminal, as soon as faceplate screws placed then current flows from N-E or N-general fabric of the building and can cause the rcd to trip? This is despite the circuit being properly isolated.
To the OP - if your husband is going to do such things, then a socket tester is a small but worthwhile investment. Helps to show the circuit is off and safe, shows (most) wiring faults. Good to have in any DIY toolkit.
cheaper ones exist if you google "socket tester'. Available in Screwfix, Toolstation, B&Q etc