How to use a multimeter to measure whether a circuit is grounded using a resistance range
How to use a multimeter to measure whether a circuit is grounded using a resistance range? Firstly, regardless of any circuit or equipment being measured, the voltage must be measured to ensure safety and voltage free before conducting other measurements. If it is a capacitor or equipment with capacitive reactance, it must be discharged first before determining safety and voltage free; Then adjust the gear of the multimeter to the 2000 megohm gear, with one end of the probe in contact with the grounding body or metal shell of the equipment, and the other probe in contact with a normally live conductor of the equipment or circuit. If the resistance is less than 0.5 megohm, it is considered grounded. Generally, leakage protectors greater than 0.5 megohm and 30 milliampere will not trip for protection, so it is generally considered that the line or equipment is not grounded. But it also depends on the working voltage or various technical requirements of the equipment or circuit.
In daily life, as for the wide range of circuits, I don't know which type of circuit you refer to. There are electronic circuits, electronic circuits that transport voltage, and electric motor circuits. Taking these three commonly used circuits as examples, let's talk about how to use a multimeter resistance range to measure grounding.
1、 Electronic circuits, in general, measuring electronic circuits should be universal
The gear of the meter is the maximum gear of 10k. At this time, the measured resistance value is almost 10K. The pointer moves slightly, and then the probes are swapped for measurement. Some electrical instruments may have different probes after swapping, resulting in less difference. In electronic circuits, high-frequency capacitors are installed to resist high-frequency interference, so it is normal to have a certain value measured to ground. Therefore, it can cause numbness in people's hands during normal times, and this circuit cannot be measured with a megger, which can damage electronic components.
2、 For voltage transmission circuits, taking household lighting circuits as an example, before measuring, the power switch must be disconnected first, and the switches of each electrical appliance must also be disconnected. Then, the grounding situation should be measured. If a multimeter is used to measure the resistance of the circuit to ground, the resistance of the live line and the zero line should be infinite. Even if a multimeter is used to measure this circuit using a 2 megohm level, it is far from enough, Because the voltage of the stacked battery inside 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 (also known as a megohmmeter), and the measured resistance value must be greater than 0 or 5 megohms to ensure that the circuit does not leak electricity.
3、 It is not advisable to use a multimeter to measure the motor circuit to ground. Similarly, a 500 volt megohmmeter should be used to measure the resistance of the coil circuit to ground. The resistance of the coil circuit to ground must also be greater than 05 megohms to be considered safe. If it is a newly wound motor coil, the resistance to ground must be greater than 10 megohms. So each type of circuit has different requirements for the resistance to ground, and the requirement for high voltage has a higher insulation resistance to ground.
