A motor control center is a purpose-built concentration of electrical fault opportunities. Each bucket contains a disconnect, a contactor, an overload relay, and the terminations feeding a motor branch circuit, and a substantial MCC holds dozens of them sharing a common vertical and horizontal bus. The equipment is well designed and highly reliable per device, but the number of connections and switching contacts in one enclosure means the aggregate probability of a developing fault is considerably higher than for a comparable volume of static distribution gear.
Contactors are the specific difference. A motor starter makes and breaks load current every time the motor cycles, which produces contact erosion and, over enough operations, pitting and increased resistance. In an application that starts frequently, that wear accumulates fast. Combined with the vibration typical of industrial environments loosening terminations, the result is localized heating that progresses from a warm connection to a carbonized insulator to a tracking path to an arcing fault.
The contamination environment accelerates all of it. MCCs in industrial settings accumulate conductive process dust, and in coastal South Florida they accumulate salt-laden humidity that leaves hygroscopic deposits on insulating surfaces. Both provide the surface tracking path that turns a marginal condition into a fault. This is why NFPA 70B maintenance, and infrared thermography in particular, prevents far more MCC fires than any suppression system controls.