How to use the multimeter to measure whether the circuit is grounded with the resistance file
How to use a multimeter to measure whether a circuit is grounded with a resistance gear. First, regardless of measuring any line or equipment, you must first measure the voltage to ensure safety and no voltage before performing other measurements. If it is a capacitor or a device with capacitive reactance, you must first discharge it before confirming Safe and without voltage; then adjust the gear of the multimeter to the 2000 megohm gear, one end of the test lead touches the grounding body or the metal shell of the equipment, and the other test lead touches the normally charged conductor of the equipment or the line, if the resistance is less than 0.5 megohm, it is grounded. Generally, leakage protectors greater 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 working voltage of the equipment or line or various technical requirements.
In daily life, as for the wide range of circuits, I don’t know which circuit you are referring to. There are electronic circuits, electric money circuits for transmitting voltage, and motor circuits. Let’s take these three commonly used circuits as examples to talk about how Use a multimeter to measure whether it is grounded.
1. Electronic circuit, under normal circumstances, the measurement electronic circuit chooses universal
The gear of the meter is the maximum gear of 10k gear. At this time, the measured resistance value is almost close to 10K, the pointer moves slightly, and then the test leads are reversed for measurement. Some electrical test leads will be different after being reversed, and the difference will be small, because in In electronic circuits, in order to resist high-frequency interference, high-frequency capacitors are installed for grounding, so it is normal to have a certain value for the ground. Therefore, it usually makes people feel numb. This kind of circuit cannot be measured with a shaker, which will damage the electronic parts.
2. The voltage transmission circuit, take the household lighting circuit as an example. Before measuring, first turn off the power switch, and at the same time turn off the switches of all electrical appliances, and then measure the grounding situation. If the measurement circuit is blocked by a multimeter The resistance to the ground, the resistance of the live wire and the neutral wire should be infinite. Even if the multimeter is used to measure this circuit with a 2 megohm block, it is far from enough, because the voltage of the stacked battery in the multimeter is only 9 volts, and the lighting voltage is in It is about 220 volts. If possible, it is best to use a 500-volt megohmmeter (to be called a shaker). The measured resistance must be greater than 0.5 megohms to ensure that the circuit does not leak.
3. It is not safe to use a multimeter to measure the motor circuit to the ground. It is also necessary to use a 500-volt megohmmeter to measure. The resistance of the coil circuit to the ground must also be greater than 0.5 megohm. The resistance of the wound motor coil to ground must be greater than 10 megohms. Therefore, each circuit has different requirements for the resistance value of the ground, and the high voltage requires a large insulation resistance value for the ground.
