HRC Fuse (High Rupturing Capacity Fuse)

HRC means “High Rupture Capacity”. The rupture capacity is the maximum current that can safely be interrupted by the fuse.

A fuse is designed to melt and break the circuit if a preset “trip current” is exceeded. However, most fuses not designated HRC can only reliably break up to about 10 times the fuse trip current.

If you have so much current that the fuse is heated so fast that some of the metal is vaporised, then this metal can be deposited on the inside of the cartridge and the current can continue flowing through it. To prevent this, HRC fuses are filled with sand to increase the area (and therefore reduce the thickness) of this deposited metal.

So the answer is, if the source of power has a low internal impedance, and can therefore feed a large current into a fault, then you need an HRC fuse to protect from it and reliably break the circuit.

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HRC Fuse Construction

An HRC fuse is a type of cartridge fuse, in which the fuse element is enclosed within a transparent capsule, usually made up of steatite–a ceramic material having good mechanical strength. Manufacturers are now using epoxy resins instead of ceramic material. The capsule is provided with two end caps. The fuse element is connected between end caps within the body. The whole setup is designed such that it can withstand the high pressure developed under short circuit conditions. Powdered quartz, which acts as an arc extinguishing agent, fills the space between the fuse element and the envelope.

Fuse Element

Silver or copper is normally used as the fuse element due to its low specific resistance. The fuse element normally has two or more sections joint by means of tin joints. Tin has a lower melting point of 240' C that is three times lesser than the melting point of silver (980' C). Hence the melting of tin joints prevents the fuse from attaining high temperatures during overload and short circuit conditions.

Advantages of HRC fuses

1. When compared to other circuit interrupters of same capacity HRC fuses are the cheaper one.
2. Simple and easy to install.
3. No maintenance required.
4. High breaking capacity.
5. They are consistent in performance.
6. Their inverse time characteristic makes them much suited for overload protection.
7. They are capable of clearing high as well as low currents.
8. Quick operation.
9. They are capable clearing high as well as low currents.
10. During severe faults, an HRC fuse breaks the circuit before the peak current of the fault is reached.