Abstract: An energy monitoring system for retrofitting a miniature circuit breaker load center 100, comprises energy monitoring module 120, data bus 140, and main controller 110. The energy monitoring module attaches onto miniature circuit breaker 130, forming a combined shape that fits into a branch circuit space of the load center. An attachment connector 320 electrically and mechanically connects the energy monitoring module to load terminal 318 of the circuit breaker. An energy sensing circuit 314 in the energy monitoring module senses energy passing through the circuit breaker and transmits data signals over the data bus to the main controller. The main controller has a shape that fits into another branch circuit space of the load center. The main controller wirelessly transmits to a network, information based on the data signals received on the data bus. The main controller provides operating power via the data bus, to the energy monitoring module.