Why is an introductory RCD triggered, not a group one?
The air conditioner is connected through a power outlet, automatic 25A, RCD 25A 30 mA. At the input is an RCD 100A 300mA. When you turn on the air conditioner, sometimes an introductory RCD is knocked out, and not a group one. Why?
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Hello! It means that the air conditioner “flows” somewhere on the case, and quite strongly, therefore the selectivity of the RCD operation is not ensured, also check the RCD of the group where the air conditioner is connected. A current leak can be in another place - in wires, on a connection and so on. For the sake of experiment, try connecting the air conditioner through an extension cord from an outlet that is connected to an automaton of another group, if any, or from an outlet that is closer to the input. If the situation is similar - 90% probability that the problem is in the air conditioner.
The next step is to at least check the resistance between the terminals of the plug and the air conditioner housing with a multimeter. Or between the power terminals of the plug and the grounding terminal. Although such measurements are carried out with a megger with a measurement voltage of at least equal to the rated voltage of the circuits being tested. The nominal resistance is conventionally taken at 1 MOhm per 1 kV, more details in PUE-7 1.8.34 onwards.
By the way, in the off condition of the air conditioner, such measurements may not give anything, because the engine chain will actually be broken. If you can do it yourself - check the engines themselves and the circuit elements with the disassembled unit, i.e. "On the wires."