What is an HRC fuse?
HRC fuse is a special type of electrical fuse that protects circuits against the effects of overcurrents. HRC fuse cannot be used individually in installations. It is either used with a carrier or placed in a fuse-switch disconnector.
Although it varies from brand to brand, HRC fuses are generally produced in sizes of 000, 00, 0, 1, 2, 3, 4, 5 up to 1600A.
Since the HRC fuse operates according to the heating principle method, its body must be made of durable materials. Steatite material, which is a derivative of porcelain, is used in its body to have high resistance against dynamic forces and heat. High purity and clean quartz sand are used in the fuse to extinguish the arc that will occur during the opening.
Other definitions of HRC fuse:
- High Rupturing Capacity Fuse (it is also the full form of HRC fuse)
- NH fuse
- Fuse link
- Knife type fuse
- HRC link
How does an HRC fuse work?
HRC fuse is designed to carry a specified amount of current continuously without opening. This is referred to as the rated current of the fuse. When an electric current flows through these element bridges or restrictions, heat is generated. Until there is a balance in heat transfer the fuse elements continue to carry the current as intended.
When there is an imbalance in heat transfer due to overcurrent conditions such as an overload or short-circuit, the amount of heat generated is greater than the heat dissipated. This causes a rise in temperature at the fusible element’s restrictions or weak points.
When this rise in temperature reaches the melting point of the fusible element, the element bridges start to melt and break, resulting in an interruption of current flow through the fuse to the circuit.
When current flows through HRC fuses, the conductor inside the fuse heats up. When the current rises above a certain level, the conductor melts and disconnects the load from the supply in just a few milliseconds. Yet during this time, an arc is generated within the fuse which in turn, is quenched or extinguished by the quartz silica sand filler material.
There are status indicators on HRCs to indicate the open or closed position of the fuse.
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Types of HRC fuses
HRC fuses have been developed over the years to suit a wide range of applications. They are available in a wide variety of opening speeds.
IEC / VDE operational classes
Full-range fuse for general use, primarily cable and line protection.
Partial-range switching device protection for electrical motor circuits.
Full-range fuses for protecting semiconductor components (faster acting than gS)
Full-range fuses for protecting semiconductor components, for increased line capacity.
Partial-range fuse for protecting semiconductor components.
VDE operational classes
Full-range fuse for equipment in the mining industry.
Full-range fuse for transformer protection rated according to apparent transformer power (kVA), not rated current (A)
Full-range fuse for cable and line protection.
Full-range fuse for cable and line protection.
Other operational classes
Full-range fuse for protecting electrical motor circuits with two rated currents. (widespread in Great Britain)
North American fuse for general use, primarily cable and line protection.
North American fuse with slow-acting characteristics for general use and motor protection.
Formerly IEC operational class (slow-acting), replaced by gG
Formerly IEC operational class (fast-acting), replaced by gG
Formerly VDE operational class, replaced by gG
Formerly VDE operational class (slow-acting), replaced by gG
Formerly VDE operational class (fast-acting), replaced by gG
Formerly VDE operational class (slow/fast-acting), replaced by gB
HRC fuse selection
When selecting an HRC fuse, these parameters should be considered:
- Type of the application. (cable protection/motor protection)
- System voltage.
- Full load current.
- Non-fault overload current. (motor inrush current etc)
- Possible fault conditions and maximum short-circuit current.
- Time-current curve.
- Cut-off curve.
Applications of HRC fuse
Some of the important applications of HRC fuses are:
- In radial and ring networks with high selectivity.
- For backup protection of MCBs.
- For the protection of motor circuits in which operational short-term overloads and short-circuits occur.
- Short circuit protection for switching devices such as contactors and circuit-breakers.
The field of application for HRC fuses includes industrial installations, power supply utilities, equipment manufacturers, switchboards, and control panels.
If you want to learn more about fuses you can check the book "Electric Fuses by A. Wright and P.G. Newbery"