The Siemens P1E‑42MC400CT is a high-capacity, heavy-duty panelboard interior designed for demanding commercial and industrial electrical distribution systems. Built to handle up to 400 amps at 277/480 volts AC, this Type P1 panelboard features a robust tin-plated copper bus system for superior conductivity and corrosion resistance. It supports up to 42 circuits, providing flexible load distribution in three-phase, four-wire systems—ideal for lighting, HVAC, or motor control in large facilities. The compact interior is only 20 inches wide and 5.75 inches deep, yet it is engineered for maximum performance and space efficiency. The unit is convertible between main lug and main breaker configurations, making it highly adaptable to different installation requirements. It also allows for feed-through lugs or sub-feed breakers up to 400 A without increasing the box height, supporting future expansion or downstream panels. The Siemens P1E‑42 interior is UL-listed, factory-built to Siemens’ strict quality standards, and designed for straightforward integration with Siemens branch breakers, providing reliable overcurrent protection and system coordination. This panelboard is a core component in any advanced power distribution system where safety, scalability, and electrical performance are critical.