A method of measuring the length of an electric cable, the method comprising: providing an electric cable (1; 30; 40; 73) having a cable length and a central longitudinal axis (Z) defining a cable neutral axis which, upon cable bending, is not subject to elongation or compression strain and, the cable including: - a longitudinal structural element (2, 7; 43, 44) including at least one electric conductor (12, 7; 45), and - a fibre unit longitudinally extending along the cable and including an optical fibre (9; 71) having a fibre length and arranged substantially along the central longitudinal axis (Z), wherein the optical fibre (9; 71) is mechanically coupled with the cable; injecting an optical signal into the optical fibre (9; 71); detecting back-scattered light from the optical fibre (9; 71) responsive to said optical signal; analysing the detected back-scattered light as a function of time so as to determine the fibre length, and deriving the cable length from the fibre length, characterised in that the optical fibre unit is embedded in a mechanically-coupling filler (6; 25; 47) that mechanically couples the optical fibre unit with the longitudinal structural element (2, 7; 43, 44), the optical fibre unit being congruent with the longitudinal structural element (2, 7; 43, 44) in such a way that the optical fibre unit remains in coaxial alignment with the central longitudinal axis (Z) and a substantially constant relationship between the cable length and the fibre length is maintained. providing an electric cable (1; 30; 40; 73) having a cable length and a central longitudinal axis (Z) defining a cable neutral axis which, upon cable bending, is not subject to elongation or compression strain and, the cable including: - a longitudinal structural element (2, 7; 43, 44) including at least one electric conductor (12, 7; 45), and - a fibre unit longitudinally extending along the cable and including an optical fibre (9; 71) having a fibre length and arranged substantially along the central longitudinal axis (Z), wherein the optical fibre (9; 71) is mechanically coupled with the cable; - a longitudinal structural element (2, 7; 43, 44) including at least one electric conductor (12, 7; 45), and - a fibre unit longitudinally extending along the cable and including an optical fibre (9; 71) having a fibre length and arranged substantially along the central longitudinal axis (Z), wherein the optical fibre (9; 71) is mechanically coupled with the cable; injecting an optical signal into the optical fibre (9; 71); detecting back-scattered light from the optical fibre (9; 71) responsive to said optical signal; analysing the detected back-scattered light as a function of time so as to determine the fibre length, and deriving the cable length from the fibre length, characterised in that the optical fibre unit is embedded in a mechanically-coupling filler (6; 25; 47) that mechanically couples the optical fibre unit with the longitudinal structural element (2, 7; 43, 44), the optical fibre unit being congruent with the longitudinal structural element (2, 7; 43, 44) in such a way that the optical fibre unit remains in coaxial alignment with the central longitudinal axis (Z) and a substantially constant relationship between the cable length and the fibre length is maintained. <EOS>