This article presents the use of a sensor with fiber Bragg grating along with an interrogation system used for monitoring the overhead lines’ wire elongation. The possible interrogation methods based on adjusted filters were considered. In the experimental part, three types of fiber Bragg grating pairs, characterized by a small shift in spectra in pairs and gratings with exact matching, were examined. The study showed that, by choosing the appropriate mechanical parameters of the elongation transformer with the optical parameters of the sensor and dedicated filter, the optomechanical system can be adjusted to the required range of overhead line wire sag observation. The range of sag depends on the distance between the poles, the wire type, and its real length in the span, which effectively determines the sag.
