A monitoring system for an electric vehicle that draws current from a conductor by means of a current collector that contacts a conductor in operation of the vehicle, the system comprising: a plurality of sensor modules configured to be distributed at spaced intervals throughout the current collector, wherein each sensor module comprises three FBG sensors, that is Fibre Bragg Grating sensors (FBG 1 to FBG 9), arranged in a common plane and configured to be laid flat on a pan head of a pantograph, each said module (FBG 1-3; FBG 4-6; FBG 7-9) being comprised only of FBG sensors that are responsive in use to both temperature and strain, wherein the sensors of each said module are in close proximity to one another so that temperature performance of the sensors is similar and are arranged in a triangular pattern with an angle of approximately 60 degrees between adjacent sensors so that temperature induced wavelength changes in the FBG sensors of each module can be compensated for; an optical source for illuminating each said sensor module; means for optically coupling said optical source to each said sensor module; and an optical signal interpretation module configured to receive optical signals from each said sensor module via said optical coupling means, said optical signals being generated by said sensor modules in response to illumination of said sensor modules by said optical source, said interpretation module being configured to be capable of mathematically correlating optical signals from at least two sensors in each sensor module to compensate for temperature induced wavelength changes in the FBG sensors of each module and thereby provide a temperature-independent strain measurement for each said sensor module. a plurality of sensor modules configured to be distributed at spaced intervals throughout the current collector, wherein each sensor module comprises three FBG sensors, that is Fibre Bragg Grating sensors (FBG 1 to FBG 9), arranged in a common plane and configured to be laid flat on a pan head of a pantograph, each said module (FBG 1-3; FBG 4-6; FBG 7-9) being comprised only of FBG sensors that are responsive in use to both temperature and strain, wherein the sensors of each said module are in close proximity to one another so that temperature performance of the sensors is similar and are arranged in a triangular pattern with an angle of approximately 60 degrees between adjacent sensors so that temperature induced wavelength changes in the FBG sensors of each module can be compensated for; an optical source for illuminating each said sensor module; means for optically coupling said optical source to each said sensor module; and an optical signal interpretation module configured to receive optical signals from each said sensor module via said optical coupling means, said optical signals being generated by said sensor modules in response to illumination of said sensor modules by said optical source, said interpretation module being configured to be capable of mathematically correlating optical signals from at least two sensors in each sensor module to compensate for temperature induced wavelength changes in the FBG sensors of each module and thereby provide a temperature-independent strain measurement for each said sensor module.