Condition monitoring is playing an increasingly important role within electrical power networks, where its use can help to reduce maintenance costs, improve supply reliability and permit increased utilization of equipment capacity by providing a measure of actual operating conditions as an alternative to relying on more stringent worst case scenarioassumptions.In this context, energy harvesting may have a role to play in that it offers the possibility of realizing autonomous, self-powering sensors that communicate their data wirelessly.In the vicinity of electrical transmission and distribution equipment,alternating electromagnetic fields at the pewer frequency offer a potential source of energy that does not require hard-wiring or batteries.There are many potentially useful locations for sensors where electromagnetic fields may be sufficient to supply a low-power wireless sensor node.This paper describes free-standingmagnetic and electric field harvesters, both for use in positions where there is ambient electromagetic field due to conductors that are remote and/or inaccessible.Using data from surveys of magnetic flux density levels at two substations, techniques for optimizing the harvester designs were obtained through theoretical analysis and experiment.A demonstrator was then constructed in which a wireless sensor becomes self-powering when immersed in a 50 Hz magnetic field.Laboratory results show that this system can deliver a useful average power of 300 μW when placed in a magnetic flux density of 18 μTrms· A similar electric field demonstrator briefly powered a temperature sensor and LCD display after exposure for 45 minutes to an electric field of 23 kV/m.