A system to measure electrical energy of current in a secondary electrical conductor connected to a primary electrical conductor, the primary and secondary conductors having substantially same voltage. The system includes a primary module including an emitter and a unit for measuring voltage of the primary conductor, at least one secondary module including a receiver, an intensity sensor of current in the secondary conductor, and a unit for calculating energy of the current. The primary module compresses the measured voltage value and emits, to each secondary module, a first message containing the compressed measured voltage value. A time synchronization mechanism performs time synchronization of each intensity sensor with the voltage measuring unit. The calculating unit is connected to the receiver and can calculate energy from the measured voltage and intensity values.