Abstract: An electricity supply network has plural switching and transformer stations connected together by cables. Each cable has an inner conductor and an outer sheath connected to housings of the stations. A communication system has plural transducers coupled to the cables at the stations. Each of the transducers is located on a side of its respective cable remote from a sheath connection of the respective cable to its station housing. Each transducer is coupled to both the sheath and the conductor of its respective cable.

Abstract: A remote electricity metering system utilizes a central station (LC) to communicate with meters (U1-U13) over the mains (10-14), with messages to remote meters being relayed by intermediate meters and the route of a message being determined by the central station. The present invention provides alarm signalling whereby the meters can communicate directly with the central station. Each meter can generate a respective combination of alarm frequencies, preferably sequentially and inside the frequency band used for normal messaging, and the local controller monitors the mains for those frequencies. An error detecting and/or correcting code can be used for the alarm frequency combinations. The central station polls the meter or meters sending the alarm. The meters are microprocessor based, with the normal message signals and the alarm frequencies being synthesized from a sequence of digital values by a D/A converter.