How can a multimeter be used to measure whether there is a leakage current in a circuit?
The safety tripping value set for the residual current circuit breaker is 30 mA. Considering such a relatively high current value, whether you use the AC range of a digital multimeter or the 10K resistance range, it is easy to detect the indication of leakage current.
When the circuit is live, first use a digital voltage tester to test the outer side of the wire. If it only shows "N", it is normal. If it shows a certain voltage value, it indicates that the wire is of poor quality or has aged, and there is a possibility of leakage current.
Turn on the AC 250V range of the multimeter. The voltage between the live wire and the neutral wire should be around 220V (with a certain tolerance), the voltage between the live wire and the ground should also be around 220V (with a certain tolerance), and there is also a voltage between the neutral wire and the ground. Depending on the power of the electrical appliances in the house, a voltage ranging from 5V to dozens of volts can be measured. This is due to the loop impedance generated by the small diameter of the neutral wire, which makes the neutral wire live. If the voltage shown between the neutral wire and the ground is high, it means that the neutral wire has a small diameter, generates heat, and is not suitable for the power of the electrical appliances in the house. High-power electrical appliances in the house should be used at staggered times.
Turn off the main circuit breaker and the branch circuit breakers, pull out all the plugs, including the indicator lights (if not disconnected, it is easy to cause misjudgment). Turn on an analog multimeter, and use the 10K ohm range to measure the resistance between the live wire and the neutral wire. It is normal if the pointer does not move.
Then measure the resistance between the live wire and the ground. It is normal if the pointer does not move.
Finally, measure the resistance between the neutral wire and the ground. It is normal if the pointer does not move.
If the pointer moves slightly during the above measurements, it proves that there is leakage current. This phenomenon is usually caused by water seepage in the walls of the kitchen and bathroom, which makes the wire joints have a slight leakage current due to humidity. When checking the circuit, first turn off the circuit breakers of the kitchen and bathroom, and then measure whether there is leakage current.
Strictly speaking, using a megohmmeter is the most accurate way to measure the leakage current of wires. However, for leakage currents within 30 mA, the 10K ohm range of an analog multimeter can detect it, and a digital multimeter will be even more sensitive.
