How to use a multimeter to measure whether the circuit is short-circuited or grounded
A multimeter measures the current on the ground wire. If there is current on the ground wire, it indicates that the phase wire is grounded. If there is no obvious current value detected in the ground wire, check whether there is current in the neutral wire after confirming that there is no electrical equipment working. If there is current, 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 range of a multimeter to check the resistance between the neutral and live wires, the resistance between the neutral and ground wires, and the resistance between the live and neutral wires. 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, the conclusions drawn from inspections vary depending on the power supply method. In the TT power supply system, the neutral wire needs to be grounded separately before entering the household, and the metal casing of electrical equipment also needs to be grounded separately. At this time, measuring the resistance value between the neutral wire and the ground wire is normally relatively low, which means that the resistance between the neutral wire and the ground wire and the live wire is short circuited. The result of your inspection is that the resistance between the neutral wire and the live wire, as well as between the ground wire and the live wire, is relatively low. You can remove the grounding of the neutral wire when entering the household and conduct the inspection again.
In the TN-S power supply system, there is a three-phase five wire system with three live wires, ground wires, and neutral wires. At this time, there will be a certain resistance value between the neutral wire and the ground wire. When using the same method of inspection, it is necessary to cut off the ground wire or neutral wire, and then use a multimeter to check the resistance value between the neutral wire and live wire, ground wire and live wire, and between live wires to determine where the short circuit is.
If it is a TN-C system, it is relatively simple. The neutral and ground wires are one wire PEN, and only the resistance between the live wires and between the PEN wire and the live wire needs to be checked.
Additionally, it should be noted that the most effective tool for checking short circuits is not a multimeter. Instead, a corresponding voltage level shaking table should be used for inspection.
