(1) Residual current devices (RCDs) are suitable for low-voltage power distribution systems where the neutral point of the power supply is directly grounded or grounded through a resistor or reactance. RCDs are not suitable for systems where the neutral point is not grounded.
(2) The neutral line N of the circuit protected by the RCD must pass through a zero-sequence current transformer. Otherwise, an unbalanced current will cause the RCD to malfunction after connection.
(3) The protective earth (PE) conductor must not pass through a zero-sequence current transformer. When the PE conductor passes through the zero-sequence current transformer, the leakage current will flow back through the PE conductor and then through the zero-sequence current transformer, causing current cancellation, and the transformer will not detect the leakage current value. In the event of a fault, the RCD will not operate and will not provide protection.
(4) The neutral line of the control circuit must not be repeatedly grounded. On the one hand, with repeated grounding, under normal operating conditions, a portion of the operating current returns to the neutral point of the power supply through repeated grounding, resulting in an unbalanced current in the current transformer. When the unbalanced current reaches a certain value, the residual current device (RCD) will malfunction. On the other hand, during a fault leakage, the leakage current on the protective conductor may also flow through the current transformer's neutral conductor back to the power supply neutral point, canceling the transformer's leakage current and causing the RCD to fail to operate.
(5) The neutral conductor (N) and protective conductor (PE) after the RCD must not be combined. If they are combined, when a leakage fault occurs or a person is electrocuted, the leakage current will flow back through the current transformer, resulting in a situation similar to (3), causing the RCD to fail to operate.
(6) The wires between the protected electrical equipment and the RCD must not touch each other. If wires touch or neutral conductors cross, the zero-sequence balance current value will be immediately disrupted, causing the RCD to malfunction. Furthermore, the protected electrical equipment can only be installed in parallel after the RCD, ensuring correct wiring, and the equipment must not be connected to the test button's wiring terminal.
