How to use the resistance level of a multimeter to measure whether a circuit is grounded
How to use the resistance setting of a multimeter to measure whether a circuit is grounded? First, no matter what line or equipment is being measured, the voltage must be measured first to ensure that it is safe and voltage-free before making other measurements. If it is a capacitor or equipment with capacitive reactance, it must be discharged first and then determined. Safe and voltage-free; then adjust the multimeter to the 2000 megohm range, with one end of the test pen touching the ground or the metal shell of the equipment, and the other pen touching the normally charged conductor of the equipment or line. If the resistance is less than 0.5 megohm, it is Ground. Generally, leakage protectors larger than 0.5 megohm and 30 mA will not trip for protection, so it is generally considered that the line or equipment is not grounded. But it also depends on the operating voltage or various technical requirements of the equipment or lines.
In daily life, there is a wide range of circuits. I don’t know which circuit you are referring to. There are electronic circuits, electricity circuits that transmit voltage, and motor circuits. Let’s take these three commonly used circuits as examples. Use a multimeter to check whether the electrical barrier is grounded.
1. Electronic circuits. Generally speaking, universal electronic circuits are chosen for measurement.
The gear of the meter is the maximum gear of 10K. At this time, the measured resistance value is almost close to 10K. The pointer moves slightly, and then the test leads are swapped for measurement. Some electrical appliances will be different after the test leads are swapped, and there will be a slight difference, because in In electronic circuits, in order to resist high-frequency interference, high-frequency capacitors are installed and grounded, so it is normal to have a certain value for ground. Therefore, people usually feel numb in their hands. This kind of circuit cannot be measured with a megger, as it will damage the electronic parts.
2. Voltage transmission circuit, taking household lighting circuit as an example. Before measuring, you must first turn off the power switch, and also turn off the switches of each electrical appliance, and then measure the grounding situation. If you use a multimeter to electrically block the measurement circuit The resistance to the ground and the resistance of the live and neutral wires should be infinite. Even if a multimeter is used to measure this circuit with a 2 megohm block, it is far from enough, because the voltage of the laminated battery in the multimeter is only 9 volts, and the lighting voltage is Around 220 volts. If possible, it is best to use a 500-volt megohmmeter (called a megger). The measured resistance must be greater than 0 or 5 megohms to ensure that the circuit does not leak.
3. When measuring the motor circuit to the ground, it is not possible to use a multimeter to measure it. It must also be measured with a 500-volt megohmmeter. The resistance of the coil circuit to the ground must also be greater than 05 megohms to be considered safe. If it is new The resistance of the motor coil to ground must be greater than 10 megohms. Therefore, each circuit has different requirements for the resistance to ground. Those with high voltage require large insulation resistance to ground.
