Methods of Using a Multimeter to Measure Whether a Circuit Is Short-circuited or Grounded
When using a multimeter to measure the current of the grounding wire, if there is current in the grounding wire, it means that the phase wire is grounded. If there is no obvious current value detected in the grounding wire, and after confirming that no electrical equipment is operating, check whether there is current in the neutral wire. If there is current, it means that there is a short circuit between the phase wires or a short circuit between the phase wire and the neutral wire.
This measurement method is the most straightforward. If the power has been cut off and it is impossible to detect the current, you can consider using the resistance range of the multimeter to check the resistance between the neutral wire and the live wire, the resistance between the neutral wire and the grounding wire, and 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 inter-phase resistance between the live wires.
Of course, for different power supply methods, the conclusions drawn from the inspection are different. In the TT power supply system, the neutral wire needs to be grounded separately before entering the house, and the metal casing of the electrical equipment also needs to be grounded separately. At this time, the measured resistance between the neutral wire and the grounding wire is normally relatively low. That is to say, if the neutral wire and the grounding wire are short-circuited with the live wire, the inspection results will show that the resistances between the neutral wire and the live wire, and between the grounding wire and the live wire are both relatively low. You can remove the grounding of the neutral wire when it enters the house and then conduct the inspection again.
In the TN-S power supply system, it is a three-phase five-wire system, including three live wires, a grounding wire, and a neutral wire. At this time, there will be a certain resistance value when checking between the neutral wire and the grounding wire. When using the same inspection method, you need to cut off the grounding wire or the neutral wire, and then use the multimeter to check the resistance values between the neutral wire and the live wire, between the grounding wire and the live wire, and between the live wires respectively to determine where the short circuit occurs. In the TN-C system, it is relatively simple. The neutral wire and the grounding wire are the same wire, the PEN wire. You only need to check the resistance values between the live wires and between the PEN wire and the live wires.
In addition, it should be noted that the most effective tool for checking short circuits is not a multimeter. Instead, a megohmmeter of the corresponding voltage level should be used for inspection.
