Monitoring electrical systems with multiple ground connection points

A method for monitoring an electrical system having multiple electrical ground connection points comprises: receiving reflectometry data; determining a measured waveform from the reflectometry data, indicative of a state of the system during a measurement time period; obtaining a predetermined baseline waveform indicative of a baseline state of the system during a calibration time period; generating a difference waveform based on the measured waveform and the baseline waveform; and analysing the difference waveform to determine if there is a change of state in the electrical system between the calibration period and measurement period. The reflectometry data may be time domain reflectometry (TDR), sequence time domain reflectometry (STDR) or spread spectrum time domain reflectometry (SSTDR). A trained classifier may be used to analyse the difference waveform. The amplitude or the location of a peak of the difference waveform may be used to determine a change in state of a ground connection. The electrical system may include a permanently earthed section of an overhead line for a railway, tram or trolleybus.