Should I tin these wires?
Tinning wires for these terminals has a couple of disadvantages:


The contact will be more tangential to the cylindrical profile resulting in a smaller contact area than if the wires were untinned and allowed to squash into a more rectangular shape.
If, for any reason, the joint gets hot the solder can start to soften, flow slightly and terminal pressure will decrease leading to further exacerbation of the problem.


On many industrial installations the wires will be pin-crimped before insertion. This reduces the risk of stray strands left out of the terminals. Some crimpers result in a square cross-section on the crimp and these work well with the flats grips on the terminals.