Some of the “plug in” MCBs are relatively a very loose fit when you consider that some MCB terminal screws need torquing up to 2.8 newton metres.
Needless to say, the screw to this terminal could have been torqued up, unlikely though it was installed before we were told to buy torque screwdrivers, but I bet it was tight.
That's the problem with some designs of box. You couldn't check if the bussbar was actually the right side of the terminal.as the mcb was clipped in before connection. I used to use one where you could fix the mcb then pull up to check if attached. Easily done if you cannot see to bottom terminal and not able to give a little tug.
