The best solution is to have the cable prepared (stripped and trimmed length) so when it is in the terminal block the insulation is not too far out (i.e. it is not showing any exposed copper conductor).So could I wrap insulating tape around the copper wire, or how else could I fix this?
Some times the reason it won't go in properly is the other conductor in the block is too long and is protruding in to the half you are trying to insert the new cable in to.