faulty breaker will not work all the way ON

[Robert D.]

this is a condo building. each apartment has its own meter in the basement. one of the breakers works only when it is 3/4 way ON. it does not work when it is in ON position all the way. what would be the safest way to replace the breaker ? I was thinking shutting off power to the unit in the basement but I dont find any switch and looks like there is a seal on the meter. so assuming I cannot switch off the power to the box...I flip all the breakers in the OFF position, this will shut off the power to all the lines, then just untie the screw, take out the breaker, put a new one, tie the screw and we back in business ? the main bar that touches the breakers is still hot though...