How to use multimeter to check whether the line is short-circuited or grounded?
If you want to check the line for short circuit. First of all, the lines should be cut off, then the load switches should be opened, and the resistance between two lines should be blocked with the ohm of multimeter. Under normal circumstances, the greater the resistance, the better. If you judge whether the line is grounded, you can use the ohm block of the multimeter. To measure the resistance of each line to ground. The bigger the better. It should be pointed out that it is not accurate to measure the short circuit and grounding of the line with a multimeter. It should not be, if the grounding or short-circuit resistance is very small, it can be detected by multimeter, if the resistance is slightly larger. The multimeter can't be checked, and it is in the low voltage circuit of 380V V. 500V shaking table should be used for measurement, whether between lines or to the ground. Should be above 0.38 megohm. Otherwise, it is unqualified.
First of all, it is necessary to separate the fire line and the zero line.
Ground wire: set the multimeter to the AC voltage range, and the range is higher than 220V V. Insert the red stylus into the voltage hole, but not the black stylus, and then insert the red stylus into one of the sockets to observe the reading.
The largest reading is the live wire, the smaller reading is the zero line, and the reading is basically the ground wire.
If two readings are small, and one reading is large, it means that the ground wire is not grounded, and the ground wire is also connected to the zero line. There is no need to measure in the second step.
Turn the multimeter to the "short circuit" test function (if there is no resistance test), and the red and black probes are connected to the ground of the circuit and the ground of the commercial power respectively. If the test result is short circuit or the resistance is extremely small, the line is grounded, otherwise it is not.
Check the leakage and grounding, and hit the multimeter to 200M m. For example, to measure the insulation of equipment, connect one end of the stylus to the equipment shell or ground wire, and the other end of the stylus to the line. When measuring insulation, hands should not touch the stylus to prevent measurement errors.
Adjust the resistance range of multimeter to 20K or 200K, turn off the main power supply and load power supply, connect the live wire and the ground wire with a multimeter, check the resistance value, then connect the zero wire and the ground wire with a probe, and watch the resistance value twice. If it appears above 7.3 or above 14, it means that the live wire or the zero wire with resistance value is leaking.
The essence of voltage is potential difference. As long as the voltage between the two lines is 0, you can use the resistance file to measure:
1. Suppose there is a short circuit between line A and line B, and there may be a voltage (for example, 220 volts) between line A and line B to the neutral line, and the potentials on their lines are potential A and potential B respectively. The first thing that many people think of is that if you measure directly with a resistance file, you must disconnect the power supply on line A and line B respectively before you can measure. This idea is not wrong, but too conservative.
2, directly dial the multimeter to the AC voltage range, choose the highest range, such as AC1000 volts, and then use the AC voltage range of the multimeter to measure line A and line B. If there is a relatively high voltage (such as 200 volts) between the two lines, it can be proved that potential A and potential B are not equal, that is to say, there is a voltage difference between potential A and potential B. These two lines are not equal in potential, and they are not shorted together.
3. If there is no voltage between line A and line B measured by AC voltage file, for the sake of guarantee, choose DC voltage file such as 1000 volt file to measure between them, and confirm that there is no DC voltage. This sample can prove that potential A and potential B are equal. Pay attention to equality does not mean that they have no voltage to zero line N. For example, line A and line B are both 220 volts to zero line N, but the voltage between them is also 0 volts. At this time, the minimum resistance file can be used to measure between these two lines.
4. As for whether the ground is measured, the above method can also be used simply. The idea is to understand the ground wire as an ordinary line. However, in general, to measure whether it touches the ground, you can use a shaking table to measure the insulation resistance (generally, the insulation is 5 megohms), and at this time, it is necessary to cut off the power to measure.
