The present disclosure relates to the determination of impedances in an electrical network. Methods and apparatuses for determining one or more impedances within a root and branch network are disclosed. The impedance of a common root part and the impedance of a branch of the electrical network may be determined based on the current in the common root part, the current in a branch of the electrical network and the voltage across the common root part and the branch. By determining the impedance of different parts of the electrical network in this way, the network may be monitored over time and the location of any faults or impending faults in the network may be identified more exactly without requiring invasive network probing and testing.