Meter Main and Meter Load Center Combinations Siemens provides a full range of Meter Combination Load Centers and Meter Mains that are built for safety ease of installation and long-term quality. A Meter Main is a device that provides a meter socket and a main breaker, a meter combination load center provides a socket, main breaker and load center interior. Siemens has also introduced a line of solar ready Meter Combination Load Centers.