Recently renovated School building. Circular saw in woodworking class, dedicated 16A 3ph circuit. Teacher wondered why saw worked so poorly. Opens receptacle, phases swapped. lol!
Concerning loose screws: Take an old switch out of the box or open a plug, and chances are good at least one of the wires will immediately fall out of the screws. In the Villa I mentioned in the DC system post EVERY switch had at least one loose wire. [Linked Image]