Square D MB250 Main Breaker

Square D MB250 Main Breaker is a 250-amp main circuit-breaker kit designed for Square D NF panelboards, providing the primary overcurrent protection for the service. Specifically labeled MB250, it is intended for NF panel interiors and uses a W-frame breaker arrangement to fit the Square D NF architecture. As a main-breaker kit, it functions as the primary disconnect and protection device for compatible NF panel systems, supporting service entrances and downstream branch circuits within the panel's rated capacity. The NF panel family supports mains up to 250 A, aligning with the MB250 rating and the kit's purpose in configuring a complete NF panel interior with a main breaker. This part is cataloged as a 250 A main-breaker option within Square D's NF lineup, and is used in installations that require a code-compliant main protection device integrated with the panel’s field-configurable interior. When paired with the correct NF interior, the MB250 kit enables a compliant, centralized main protection solution for commercial or residential electrical service.