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The time and current operating characteristics of fuses are chosen to provide adequate protection without needless interruption. Wiring regulations usually define a maximum fuse current rating for particular circuits. A fuse can be used to mitigate short circuits, overloading, mismatched loads, or device failure. When a damaged live wire makes ...
IEC 60269 unifies the electrical characteristics of fuses that are dimensionally interchangeable with fuses built to earlier British, German, French or Italian standards. [2] The standard identifies application categories which classify the time-current characteristic of each type of fuse. The application category is a two-digit code.
For low-voltage distribution circuit breakers an international standard, IEC 60898-1, defines rated current as the maximum current that a breaker is designed to carry continuously. The commonly available preferred values for rated current are 1 A, 2 A, 4 A, 6 A, 10 A, 13 A, 16 A, 20 A, 25 A, 32 A, 40 A, 50 A, 63 A, 80 A, 100 A, [ 6 ] and 125 A.
Breaking current may be stated in terms of the total current or just in terms of the alternating-current (symmetrical) component. Since the time of opening of a fuse or switch is not coordinated with the reversal of the alternating current, in some circuits the total current may be offset and can be larger than the alternating current component ...
Instantaneous overcurrent requires that the current exceeds a predetermined level for the circuit breaker to operate. Time overcurrent protection operates based on a current vs time curve. Based on this curve, if the measured current exceeds a given level for the preset amount of time, the circuit breaker or fuse will operate.
An inverse-time over-current (ITOC) relay is an overcurrent relay which operates only when the magnitude of their operating current is inversely proportional to the magnitude of the energize quantities. The operating time of relay decreases with the increases in the current. The operation of the relay depends on the magnitude of the current. [33]
AFCI circuit breakers include a standard inverse-time circuit breaker but provide no specific protection against "glowing" connections (also known as a high resistance connection), high line voltages, or low line voltages. An AFCI does not detect high line voltage caused by an open neutral in a multiwire branch circuit.
Current interruption in a high-voltage circuit breaker is obtained by separating two contacts in a medium, such as sulfur hexafluoride (SF 6), having excellent dielectric and arc-quenching properties. After contact separation, current is carried through an arc and is interrupted when this arc is cooled by a gas blast of sufficient intensity. [1]