K— circuit breakers with this tripping characteristic are designed for circuits with an exclusively inductive load — that is, the power supply of electric motors, transformers, some types of powerful lamps and other similar devices, a characteristic feature of which is a high (several times more than the rated) starting current.
Thus, the protective characteristic K provides rather specific tripping rules. So, the electromagnetic release (which is responsible for the instantaneous shutdown of the machine) in such devices works differently: in AC circuits — when exceeded by 12 times, constant — by 18 times. In turn, the thermal release, which has a relatively long response time, opens the circuit when the rated current is exceeded by only 5%. The idea of this format of work is that the usual inrush current flows through the circuit in literally a fraction of a second; if the current strength exceeds the rated current for a longer time (sufficient for the thermal release to operate), then this, usually, is no longer the starting current, but a sign of a malfunction that requires turning off the power.
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