Breaking capacity of fuses

Breaking capacity of fuses

The breaking capacity gives the current that a fuse is able to interrupt without being destroyed or causing an electric arc with unacceptable duration. The maximum short circuit current which can occur under fault conditions should not exceed the rated breaking capacity of the fuse. Otherwise breaking of the fault current cannot be guaranteed.

Choosing breaking capacity

Calculating a suitable breaking capacity involves determining the supply impedance and voltage. Supply impedance may be found by
* measurement
* reading datasheet
* or the PSCC value requested from utility supply company

Importance of breaking capacity

Some applications have inherently limited and low PSCC, and in these cases often all available fault current protectors will suffice. This is typical for supplies from small & miniature transformers, which can have anything up to 33% regulation.

On the other hand some applications may tend to have high PSCCs, with fault currents able to do extensive damage and endanger human life. Breaking capacity is highly important in these cases. Examples include electrical substations.

Common Breaking Capacities

* 20mm glass fuse: 35A or 10x rated current value
* 20mm sand filled ceramic fuse:
* 1.25" sand filled ceramic fuse:
* Thermal mcb, 240v: 3kA
* thermal & magnetic mcb, 240v: 6kA
* 100A incomer fuse, UK:

See also

* Maximum prospective short circuit current

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