I need help from an electrician with a problem!
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Hello everyone: Today, I encountered a situation. The workshop is powered by a 380V supply, which is used regularly. Today, the residual current device in one of the distribution boxes tripped. I unplugged all electrical appliances connected to the outlets downstream of that box and then conducted tests. With power applied above the residual current device, the voltage between each phase was measured at 410V, which is normal; the voltage of each phase relative to ground was 230V, also normal; and the voltage of the neutral wire relative to ground was 2V, which is normal as well. The resistance between the neutral and ground wires was 130 ohms. After turning off the circuit breaker in the main distribution box, there was no electricity upstream of the circuit breaker in this sub-distribution box; the resistance between the neutral and ground wires was infinite in this case. After a while, this tripped RCD can be turned back on. I would like to ask why, when power is applied, there is resistance between the neutral and ground wires, and why this resistance is so low – it seems as though the wires are damaged. However, when the power is turned off, the resistance between them becomes infinite, and the buzzer function does not work; in this case, the wires aren’t damaged. What’s going on? Is there any master who knows about this? Please feel free to offer your advice. Thank you!
To measure resistance, a multimeter cannot be used; instead, a megohmmeter is required.
Based on your description, this situation might be caused by a wiring fault or a short circuit. After the residual current circuit breaker in the distribution box trips, when electrical appliances plugged into the sockets are unplugged, the resistance value between the neutral wire and the ground wire increases, indicating that there is no leakage or short-circuiting at this time. However, when the RCD on the main distribution box is turned off, the RCDs on the sub-distribution boxes can be turned back on, indicating that there is a leakage or short-circuit condition at this time. This may indicate a ground fault in the circuit, resulting in a low resistance between the neutral wire and the ground wire. Since it is not possible to detect specific faults remotely, it is recommended that you hire a professional electrician to conduct an on-site inspection and repair in order to ensure the safe operation of the electrical circuit. Please do not attempt to repair the circuitry yourself, as this may cause more serious problems. .