Optical method and apparatus for monitoring an electric conductor

A railway overhead power supply electrical cable (2, 21-25) optical monitoring procedure has Bragg grating fibre optical sensors (41-45, 51- 56) in cable components fed from the catenary (21-25) so that a light signal (LS) fed into the cable is modified to give temperature (M1,2) or strain measurements at the sensor location. Includes Independent claims for equipment using the procedure.