Cables and conductors protection, part I: cables

The objective of the work is to show the requirements of the protection of cables against overcurrents, proposing an application guide, maximising the use of its load capability. It is analysed the behaviour of the cables in front of short circuits and overcurrents, explaining the thermal and electrodynamical limitations. The operation of the current limiting and expulsion fuses is studied. The methodology is presented to specify the curves current-time of the cables. It is considered the heating by the overcurrents in the conductor, screen and shield, calculating the life loss following the Arrhenius law. As a result it is in detail indicated the procedure of coordination of the characteristic curves of the cable and fuses, pointing out the best fuse. It is concluded that the low voltage high breaking capacity (HBC) and expulsion fuses possess appropriate characteristic curves for cable protection.