What is the meaning of "K" in "ABB K25" air switch?

K in air switch refers to the K characteristic patented by ABB company, which is mainly used in motor systems with rated current below 40A.

Air switch c is the classification of circuit breakers. The trip characteristics (curves) commonly used in the world are: A, B, C and D trip characteristics.

A features: 2 times rated current, rarely used, generally used for semiconductor protection;

B characteristics: 2~3 times the rated current, generally used for transformer side secondary circuit protection;

C characteristics: 5~ 10 times the rated current, which is the most commonly used, generally used for building lighting electricity, etc.

D characteristics: 10~20 times the rated current, generally used for power distribution.