50 Point Explanation
Interrupting Rating (I.R.)
N.E.C. 110.9 requires that the interrupting rating of fuses and
breakers not be less than the maximum available short circuit
current at their point-of-application.
Circuits where fuses and breakers are installed may
be capable of thousands of amperes of short circuit current
flow during a short circuit condition. When fuses or breakers
are installed where the value of short circuit current flow may
exceed the interrupting rating of the devices, a very serious
safety hazard may exist. A flow of short circuit current in
excess of the device interrupting rating may cause only a
mild device rupture during device opening or a violent explosion
depending on the value of excess short circuit current flow.