The usage method of using a digital multimeter to check whether the circuit is grounded.
Set the digital multimeter to the resistance range above 20K and measure the insulation between phases respectively.
To measure the grounding of the circuit, measure the circuit against the outer casing of the electrical equipment. If the grounded circuit touches the outer casing of the equipment, the resistance value is usually above several hundred ohms, or even zero.
This is exactly how I measured the control wires of the crane.
If you simply measure the resistance of the circuit to the ground, it is not easy to measure with a multimeter. It is recommended to use a resistance meter for measurement.
Method 1 for judging whether the ground socket is grounded:
1. First, distinguish the live wire, neutral wire and ground wire. Set the multimeter to the AC voltage range, and the range should be higher than 220V. Insert the red test lead into the voltage hole, and don't insert the black test lead. Then insert the red test lead into one of the sockets and observe the reading. The socket with the largest reading is the live wire, the one with a smaller reading is the neutral wire, and the one with almost no change in reading is the ground wire. If there are two readings that are small and one reading that is large, it means that the ground wire is not grounded and the ground wire is connected to the neutral wire. Then there is no need to carry out the second step of measurement.
2. Measure the ground wire. After distinguishing the live wire, neutral wire and ground wire, keep the multimeter in the same range (AC range above 220V), insert the red test lead into the voltage hole and the black test lead into the COM hole. Use the two test leads to measure the voltage between the live wire and the neutral wire, and the voltage between the live wire and the ground wire. If these two voltage values are basically the same, it indicates that the ground wire is grounded. If the voltage value between the live wire and the ground wire is basically zero or extremely small, it means that the ground wire is not grounded.
Method 2:
1. Set the digital multimeter to the resistance range above 20K and measure the insulation between phases respectively.
2. Measure the grounding of the circuit, measure the circuit against the outer casing of the electrical equipment. If the grounded circuit touches the outer casing of the equipment, the resistance value is usually above several hundred ohms, or even zero.
3. This is how I measured the control wires of the crane.
4. If you simply measure the resistance of the circuit to the ground, it is not easy to measure with a multimeter. It is recommended to use a resistance meter for measurement.
