Tinning wires that will be screwed in to a chocolate block/terminal strip
You MUST NOT fully tin the copper wires to be inserted into a screw down terminal block - that your days may be long on the face of the land.
It is permissible to tin the tip to maintain the wire shape.
The minimum possible amount of copper should be tinned.


Any competent regulatory authority will have this requirement as a rule in their system (see below)

The reason for the prohibition is that when you fully tin a multistrand wire fully, the solder wicks between the strands of copper and forms a solid block, part of whose volume is metallic solder. When you clamp the solder and copper bundle you tighten the screw or clamp against the solder block, and in time the solder metal "creeps" under the compressive forces and the join loses tension. The wire can then either pull out or cause a high resistance connection with heating. 

This is a genuine real-world issue and is covered by genuine real-world regulations in many countries.