Abstract: The invention provides a system (1) for providing power measurements using a current sensing element (2) located at a supply line and a voltage sensing element (3) located remotely from said supply line location. Power measurement is enabled by using a communications link (4) to correlate current and voltage measurements.

Abstract: A method of inference of appliance usage from a point measurement on a supply line, said supply line being common to multiple appliances and/or components of appliances comprises the steps of: obtaining data from said measurement point; sampling power and reactive power at intervals substantially throughout periods of operation of said appliances or components of appliances corresponding to appliances or components of appliances being in ON and/or OFF modes of use; identifying characteristics of events by assessing power and reactive power change during an event; and by assessing one or more additional characteristics derivable from said power and reactive power to characterise an appliance; grouping events and/or cycles of events into clusters of similar characteristics; and inferring appliance usage based on said grouping.

Abstract: Apparatus for monitoring the voltage of electricity supplied on a cable (121) are described. The apparatus includes a sense electrode housed in an electrically-insulative housing to form a capacitive coupling (127) between the sense electrode and the cable. The housing may be of the clamp-on type. A sense capacitor (128) of known capacitance is included, which is electrically coupled to the sense electrode and a local ground. Suitable voltage measurement circuitry (126) is connected to the sense capacitor and is responsive to voltage produced across the sense capacitor to provide an output signal representative of the voltage on the cable. The measured voltage waveform can be filtered to give the fundamental of the supply voltage, which can eliminate or reduce the effects of changes in capacitance within one cycle. A secondary capacitive (130) coupling can be formed with a related neutral wire (122) to improve stability of the voltage waveform measurement.