How to use the resistance file to measure whether the circuit is grounded or not, first of all, regardless of measuring any line and equipment, first measure the voltage to ensure safe and voltage-free, and then perform other measurements. If it is a capacitor or a capacitive reactance device, discharge it first, then determine Safe and no voltage; then adjust the multimeter's gear position to 2000 Megohm position, one end of the test pen contacts the grounding body or the metal casing of the equipment, and the other test lead contacts the normal electrified conductor of the equipment or line. If the resistance is less than 0.5 megohm Ground. Generally, a leakage protector larger than 0.5 megohm and 30 mA does not trip protection, so it is generally considered that the line or equipment is not grounded. But it depends on the operating 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, electronic circuits, electric money circuits that carry voltage, motor circuits, etc., let’s take these three commonly used circuits as an example. Use a multimeter to block the grounding.
First, the electronic circuit, under normal circumstances, the measurement of electronic circuit selection universal
The gear of the table is the maximum gear 10k gear. At this time, the measured resistance is almost 10K, the pointer is slightly moved, and then the test pen is adjusted. Some electrical instruments will be different after the adjustment, and there will be little difference, because In the electronic circuit, in order to resist high-frequency interference, the high-frequency capacitor is grounded, so it is normal to have a certain value for the ground. Therefore, people often feel a numbness. This circuit cannot be measured with a shaker and can damage electronic components.
Second, the voltage transmission circuit, taking the household lighting circuit as an example, the power switch should be disconnected first before the measurement, and also the switch of each electrical appliance should be disconnected, and then the grounding condition should be measured. If the multimeter is used to block the measurement circuit For the resistance to ground, the resistance of the zero line of the live line should be infinite. It is not enough to measure the circuit with a 2 megaohm. This is not enough because the voltage of the laminated battery in the multimeter is only 9 volts. 220 volts or so, if conditions are met, 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.
Third, the motor circuit to the ground measurement, using a multimeter to measure is not, the same with a 500 volt megohmmeter to measure, the resistance of the coil circuit to the ground is also greater than 05 megohms, it is safe, if it is new The resistance of the wound motor coil to ground must be greater than 10 megohms. Therefore, the resistance of each circuit to the ground has different requirements, and the requirement of high voltage has a large insulation resistance to the ground.
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