Abstract: A branch circuit monitor module for monitoring electrical properties of electrical branch circuits comprises one or more detectors, each detector for measuring an electrical property on a respective branch circuit and outputting a measurement signal; processing means for processing the measurement signal to generate digital output data based on the measurement signal; and means for outputting the output data. By using a modular approach to branch circuit monitoring, the user can tailor the selection of modules to his requirements; by providing digital processing means directly at the branch circuit monitor module instead of remotely, accuracy and reliability can be improved. The invention extends to a system comprising a plurality of branch circuit monitor modules. The invention also extends to a method of synchronising first and second measurement modules as well as a corresponding system.