KA stands for intermediate relay.
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intermediate relay: Used in relay protection and automatic control systems to increase the number and capacity of contacts. It is used to transmit intermediate signals in the control circuit. The structure and principle of the intermediate relay is basically the same as that of the AC contactor, and the main difference with the contactor is that the main contact of the contactor can pass through a large current, while the contact of the intermediate relay can only pass through a small current. Therefore, it can only be used in control circuits. It generally has no main contact, because the overload capacity is relatively small. Therefore, it uses all auxiliary contacts, and the number is relatively large. The new national standard defines the intermediate relay as K, and the old national standard is KA. Generally, it is powered by DC power supply. A few use AC power.