Yea, the MK terminals accept 16mm - But you want to try squeezing in back into a backbox. I reckon the OP would get trough a couple trying!
And why is it all DIYers end up with the sheath stripped back above the ceiling? Because they dont form the cables - Just terminate and push home!
And why is it all DIYers end up with the sheath stripped back above the ceiling? Because they dont form the cables - Just terminate and push home!