Abstract: A method and apparatus for detecting partial discharges in cables and accessories. An electrical interruption is created in, for example, the sheath conductor of a cable, and the voltage of high frequency signal components, created by a partial discharge, is measured across the interruption. The interruption is short-circuited to allow low frequency signals to pass across the interruption, thus preventing low frequency signals from being measured. This is useful because the signal/noise ratio of the frequency range measured according to this invention is more favourable. Also, in order to properly and accurately measure a partial discharge, it is important to relate measurements to the main supply voltage of the cable. The present invention also provides a method wherein prior to display the signal is combined with a signal representing the main supply voltage.