How to use a multimeter to test the quality of the grounding wire of a household socket?
Set the multimeter to the 250V~ AC voltage range or the range closest to and greater than 220V, and measure the voltages between the live wire and the neutral wire, as well as between the live wire and the ground wire respectively.
If the difference between the two sets of voltages is less than 5V, it proves that the ground wire is well - grounded. Moreover, the smaller the difference, the better the grounding quality.
Bulb Test
Take a light bulb. Connect one end to the live wire and the other end to the neutral wire and the ground wire respectively, and compare the brightness of the bulb in the two cases.
If the brightness is the same in both cases, or the bulb is slightly dimmer when connected to the ground wire, it indicates that the ground wire is well - grounded. If the bulb does not light up when connected to the ground wire, it means there is a fault with the ground wire.
Note: When using this method for testing, there should be no residual current device (RCD) in the circuit. Otherwise, the RCD will trip when testing the ground wire, making the comparison impossible. This device is even cheaper than a multimeter, costing about 10 yuan. Many brands produce it, and ordinary households should keep one on hand.
It is also quite convenient to use. Simply plug it into the socket, observe the sequence of the three lights on the detector, and refer to the examples to know whether the ground wire is normal (it can also detect faults in the live and neutral wires). Of course, like the previous two methods, it can only tell whether the ground is connected, and the specific grounding quality cannot be determined.
The resistance value of a well - grounded wire is about 4 ohms.
First, press the test button on the RCD to check if it works properly.
When the power is on, I used a pointer multimeter to measure the voltage difference between the neutral wire and the ground wire. Only when the multimeter was set to the 10V AC range could I measure a voltage of 3 to 5V. Therefore, to measure whether the ground wire is well - grounded, you can use a multimeter to detect these two wires. If there is no small voltage, it indicates that the ground wire is broken.
If there is a grounded metal water pipe at home, after turning off the power, use the ohm range of the multimeter to measure the resistance between the neutral wire and the ground wire. Since the age of water pipes varies from household to household, the resistance values also differ. However, if the measured resistance between the water pipe and the ground wire is within 6 ohms, it can be used. Measuring the resistance between the neutral wire and the ground wire when there is no power can best reflect whether the ground wire is qualified. The larger the resistance, the more unsafe it is!
Set the multimeter to the 50mA current range. When the power is switched on, connect one test lead of the multimeter to the neutral wire and touch the other test lead to the ground wire. If the RCD trips instantly, it means the grounding is good.
Since the minimum sensitivity of an RCD is 15mA, if it can trip in this small - current range and the current flows from the neutral wire to the ground, it means the household ground wire is qualified.
