In most cases you use solid wire. In case you use stranded you should crimp the ends anyway, and crimping does exactly opposite, crushes wires so tightly they form practically solid metal.
Strands only break when wire moves and that would be the fault of bad stress relief, not "screwing it too hard"
I have seen lots of near-fires/melted things from under-tightening, but I have never seen a single near-fire from overtightening. I suspect it's a myth - I don't think you could overtighten any connector sufficiently to make it be a fire risk without the screw shearing first.
I'd be interested to see tests demonstrating otherwise though.
Obviously if you are doing it to the standards, you crimp the wire first and use a torque screwdriver to tighten to the exact correct torque.
> I have seen lots of near-fires/melted things from under-tightening, but I have never seen a single near-fire from overtightening.
That depends what you see as near-fire ;) I recently helped out a friend whose lights had issues after she installed a more powerful fixture, turns out that the person installing it overtorqued the wire in the switch so much it nearly sheared off probably already during installation, and came completely apart when I took the switch out of the wall.
