You both may be talking about different impact drivers. One is a hand held tool you smack with a hammer to loosen tight screws, the other is a cordless screwdriver with a ratchet action.
Yes I am referring to portable 18V impact screwdrivers that look like a drill that vibrates the screw in to the material being fixed to and serves as a super fast unscrewing tool when undoing screws. (Cordless tool with a ratchet action).
Ok UP, yes that's where the confusion came from, but again although I use a cordless i'd only use it for screwing into or out of wood or brickwork etc, not for electrical connections into accessories.
Electrical Impact Drivers were primarily developed for inserting screws, not undoing them. Initially for big wood screws in construction First Fix etc The fact they undo stuff quite well is just a useful by-product!
They really can be quite useful, how many times have you tried to tighten a cheap main switch terminal and virtually twisted it out of the plastic with the switch nearly splitting in two? an Impact driver if used delicately will concentrate the torque onto the screw itself without twisting round the whole connection, its a much better way of tightening and undoing some screws without the collateral damage. Quick too. Dont use it live though I doubt they are VDE rated.
My 10.8V Makita ratchet does the job nicely on busbars on CUs, just have to know to go steady on the trigger
I will guess cable is too thin. If the terminal binds before it is tight then a torque screw driver will tighten the screw but the wire is still not clamped. I have had this with a flex where one strand has got into the threads so screw feels tight but wire is loose. Also poorly taped terminals. With the latter once they heat up it expands the thread so when checking it seems as if never tightened up. I always test the screw will actually tighten up. If the cable was doubled up in the terminal likely it would be OK. Also simply not twisting cable can mean it will not be tight. I have had it with small flex cables where although screw is very tight slight tug and cable comes out.