Use a multimeter to measure whether the circuit is shorted or grounded
The multimeter measures the current in the ground wire. If there is current in the ground wire, then the phase wire is grounded. If there is no obvious current value in the detection ground wire, check whether there is current in the neutral wire after confirming that there is no electrical equipment working. If there is current, then it is a phase-to-phase short circuit or a phase-to-neutral short circuit.
This measurement method is the most direct. If the power has been cut off and the current cannot be detected, you can consider using the resistance file of the multimeter to check the resistance between the neutral wire and the live wire, the resistance between the neutral wire and the ground wire, and the resistance between the neutral wire and the ground wire. The resistance between the live wire and the neutral wire, of course, if it is a 380V power supply, you also need to check the phase-to-phase resistance between the live wires.
Of course, different power supply methods lead to different conclusions. In the TT power supply system, the neutral line needs to be grounded separately before entering the home. The metal casing of the electrical equipment also needs to be grounded separately. At this time, measure the neutral line and ground. The resistance value between the wires is relatively low under normal circumstances, that is to say, the neutral wire, the ground wire and the live wire are short-circuited. The result of your inspection is that the resistance between the neutral wire and the live wire, and the ground wire and the live wire are relatively low. Remove the grounding when the neutral line enters the home and then check it.
In the TN-S power supply system, it is a three-phase five-wire system. There are three live wires, ground wires, and neutral wires. At this time, there will be a certain resistance between the neutral wire and the ground wire. The same method needs to be checked. Cut off the ground wire or the neutral wire, and then use a multimeter to check the resistance between the neutral wire and the live wire, the ground wire and the live wire, and the phase-to-phase of the live wire to determine where the short circuit is.
If it is a TN-C system, it is relatively simple. The neutral wire and the ground wire are one wire PEN. It is only necessary to check the resistance value between the phases of the live wires and between the PEN wire and the live wire.
In addition, it needs to be explained: the most effective tool for checking short circuits is not a multimeter, but a megger corresponding to the voltage level should be used to check.
