How to measure short circuit and ground with a multimeter

Use a multimeter to measure short circuit and grounding. What we are talking about here is basically strong electricity. In fact, weak electricity can also have short circuit and leakage.

Let's take a strong current as an example. The 380v/220v circuit is explained using 220v:

1. Live operation

Set the multimeter to AC 400V or higher (higher than 230V will be fine), and measure the voltage between the live wire and the ground. If the voltage is lower than 220V, it means that there is a leakage between the live wire and the ground wire. If you are still worried, measure the voltage between the neutral wire and the ground. Generally speaking, if the three-phase imbalance is not large, the neutral wire and the ground wire have the same potential, and there is no voltage between them, which should be 0V. However, in the case of a live wire leakage, the measured voltage must be around 180V. Therefore, if there is a leakage between the live wire and the ground wire, the live wire leakage is relatively large, and generally the leakage protection cannot be activated.

If the neutral line is leaking to the ground, disconnect all loads, push on the leakage protector, the neutral line current is zero, even if it touches the ground, it is difficult to trip the leakage protector. In this case, the tripping usually occurs only after the electrical appliances are used. The current passes through the loop to make the neutral line energized, and then connected to the ground. If the current exceeds 30ma, the leakage protector will inevitably trip.

The above is a ground fault

If there is a short circuit, it means that the live wire and the neutral wire touch each other without passing through the electrical appliances, or the live wire leaks to the ground and the neutral wire also leaks to the ground. In this case, the air switch at home will directly trip and cannot be closed. Then there is no power under the circuit breaker. Use the multimeter resistance block to measure the live wire and the neutral wire. If there is resistance, it means a short circuit. If there is no resistance, it means that there are too many electrical appliances and the overload protection circuit breaker trips, or the contact resistance caused by the virtual connection of the wire ends is too large to cause overheating and overload protection.

2. Operation without power supply

Set the multimeter to the resistance range, and measure the lower end of the circuit breaker to be tested. Use the red and black test leads to directly measure the live wire to ground and the neutral wire to ground. If there is a buzzer or resistance value, it means that the live wire and the neutral wire are leaking to the ground. If there is resistance between the live wire and the neutral wire, it means a short circuit! The best way is to use a megohmmeter to measure the insulation between the phases and the ground, provided that the load and the main switch are disconnected, because some slight leakage or moisture cannot be detected by the multimeter, and it is difficult to check if the power trips at irregular intervals.