Definition

HRC fuses, known as High Rapturing Capacity, are vital in electrical systems. They prevent catastrophic damage caused by excessive current. Fuses contain a fusible element in a heat-resistant housing. This element, usually silver, melts under high currents, breaking the circuit and preventing damage to connected equipment.

Construction of HRC Fuses

HRC fuses are made of. This ceramic body is fitted with metal end caps that are securely welded to the element that carries the silver-based current. The interior of the fuse body is filled with a powdered material, usually consisting of quartz, calcined gypsum, dust, marble and similar substances. This filler material is used to regulate the current and prevent overheating. Any heat generated causes the melted element to evaporate, which triggers a chemical reaction between the filler powder and the silver vapour, resulting in a high resistance material that helps to reduce arcing within the fuse.

Typically, copper or silver is used as the fuse element due to its lower resistivity. The element usually consists of two or more parts connected by a tin connector. Tin has a melting point of 2400°C, which is lower than the 980°C of silver. The tin connector therefore acts as a temperature protector, preventing the fuse from reaching too high a temperature in the event of short circuits and overloads.

Principle of operation of HRC fuses

Under typical operating conditions, the current flowing through a fuse lacks the energy required to cause deformation of the fuse element. However, when a large amount of current exceeds the fuse, it causes the fuse element to melt before reaching peak fault current.

Under overload conditions, the fuse element does not melt immediately. However, prolonged exposure to overload conditions may cause the fuse element to dissolve and fracture, especially in materials such as eutectic.

In the event of a short circuit, the thinner portion of the fuse element, which has a smaller area, will quickly dissolve and break before the eutectic material does. This emphasises the need to impose limits on the fuse elements in high Rapturing capacity (HRC) fuse designs.