Monitoring arrangement

A monitoring arrangement 10 for monitoring a parameter value associated with an AC supply or an AC component of a supply in a distribution network, the monitoring arrangement comprising a sensor arrangement 14 electrically connected, in use, to the network or otherwise monitoring the network, and a control unit 16 operable to use the output of the sensor arrangement to determine, for a voltage, an amplitude value for a selected frequency. The method allows the operation of the device 20 to be controlled depending on the supply from the network, without relying on signal components from rotating power converters. The device may be an electrical storage device, a smart electrical device or an electrical heating device such as a storage heater or water heater. The arrangement may conduct spectral analysis of the waveform to derive the amplitude value.