The reason why the residual current transformer can have a protection function during operation is that it can make the sum of the complex current flowing to any node in the circuit be zero. If the entire line is normal, the current transformer will not have a corresponding Signal output, then of course the various actuators in the circuit will not have any action.
Once a fault occurs in the circuit, the total current of each phase cannot be zero. The remaining current will generate magnetic flux in the ring core of the transformer, which will drive the actuator to act and finally achieve the purpose of protective grounding. Its wiring method is actually very difficult, as long as a current transformer is installed on each of the three-phase lines, or the three-phase wires are passed through the residual current transformer together, and the result will be the same.