High-voltage current limiting fuse-links are widely used for the protection of distribution cables and transformers. They commonly form part of fuse-switch combination units, or in some cases they are used as stand-alone devices to provide the sole protection of equipment. Their particular advantages are their low first cost, their small dimensions and their ability to limit the peak fault current and let-through energy of a short-circuit fault to a small fraction of the prospective value. Well-designed fuse-links can limit the fault energy to around one 500th of what a conventional circuit breaker would let through. High rupturing capacity (HRC) fuse-links, therefore, give the applications engineer the opportunity to limit the damage which would otherwise result in the event of a short-circuit fault. The disadvantages of the HRC fuse-link include the necessity of stocking and carrying spare fuses and the need for manual intervention to replace a fuse, or fuses, in the event of a fault. In addition, unlike a circuit breaker, they are unable to detect zero sequence currents and, therefore, they will not operate on an earth fault that has a magnitude which is less than the rating of the controlling fuse-link. However, many of the applications for controlling transformers and cables in secondary electrical distribution circuits successfully employ HRC fuse-links.