PowerMark PRO main breaker plug-on neutral load centers arrive with a main circuit breaker installed for a convenient and swift install. Main circuit breakers allow for the user to stop the flow of electricity in the load center, shutting off all the power in the residence. The PM1212C features spaces for 12 - 1" circuit breakers and 24 circuits, a 125-ampere bus rating, copper bus bars, and a gray combination/flush enclosure.