@roger,
roger wrote:It may have been designed to only open when the switch is in the open position, or something like that.
That makes sense. I don't think the OP mentioned voltage (let me guess, 480?), but with 200 amps of 3-phase power, it sounds like it might be a Very Bad Idea to take apart the box when live current is running through it.
It might be time to summon a licensed electrician.