We were having a new refrigerant monitor system installed in the plant and the service tech asked where the breakers were located for the two areas he was was installing the equipment. Locating the one for the main monitor was easy, everything was marked. The remote monitor wasn’t that clear cut. After locating a panel I saw a breaker marked flow meter. We used to have a city water pressure monitor installed where the new remote monitor was being mounted, so I switched it off. Bad idea. it shutdown the boilers! While I was trying to get the boilers back online, the service tech come by and said he didn’t need the breaker off, he installed while the circuit was live. A plant shutdown, switching a 20 amp breaker off, wasn’t required. I hate when these incidents are self induced. Oh, the breaker was for the steam flow indicators.
Make sure your MCC breakers are clearly marked before experimenting to find the right one.