Two optical fiber units over the semi-conducting swellable tape(s) shall be applied as distributed temperature sensor. An optical fiber unit shall consist of three multi-mode optical fibers enclosed with a stainless steel tube and the interstices between the tube and the optical fibers shall be filled with suitable jelly. Additional optical fiber(s) maybe enclosed in the optical fiber unit at manufacture's option.

These types of power cable are very useful to measure distributed temperature. The sensing fiber located close to the cable core, provides a better indication of conductor temperature.