When I wire-nut stranded to solid (often with fixture wires, and the fixture wires much smaller than the solid) I put a couple of small zig-zag bends in the solid before I spiral-wrap the stranded (stripped a little longer) around the solid. The tapered thread of the wire nut clamps the stranded to the solid and the bends prevent the solid from being pulled out.
I can reliably attach #16 or #18 fixture wires to #12 solid and never have them pull apart.
It's actually more around 370 degrees. If you have a poor solder joint, perhaps cold or weak, it could end up with enough resistance to heat it up.
Originally Posted by jadnashua