Abstract: A monitoring system for an electric vehicle that draws current from a conductor by means of a current collector (3, 7) that contacts a conductor (13) in operation of the vehicle, the system comprising: a plurality of sensor modules distributed at spaced intervals throughout the current collector, wherein each sensor module comprises a plurality of FBG (Fibre Bragg Grating) sensors orientated so as to be at least generally co-planar with a surface of the current collector that conducts the conductor in operation of the vehicle, the sensors of each said module being arranged in a geometric pattern that compensates for temperature induced wavelength changes in the FBG sensors of each module; an optical source (15) for illuminating each said sensor module; means (19) for optically coupling said optical source to each said sensor module; and an optical signal interpretation module (17) configured to receive optical signals from each said sensor module via said optical coupling means, said optical signals being gen