Method for measuring the length of an electric cable that uses an optical fibre element as a sensor

The present invention relates to a method of measuring the length of an electric cable, the method comprising: providing an electric cable having a cable length and including a cable neutral axis, and a fibre unit longitudinally extending along the cable and including an optical fibre arranged substantially along the neutral axis, wherein the optical fibre is mechanically coupled with the cable; injecting an optical signal into the optical fibre; detecting back-scattered light from the optical fibre responsive to said injected optical signal; analysing the detected back-scattered light as a function of time so as to determine the length of the optical fibre, and deriving the cable length from the length of the optical fibre.