Multimeter test method for checking whether a line is shorted or grounded
If you want to check the line for shorts. Firstly, you have to de-energise the line, then pull the individual load switches apart and use the ohm stop of your multimeter for the resistance between the two two wires. Under normal circumstances, the higher the resistance, the better. If you judge whether the line is grounded or not, you can use the ohm stop of the multimeter. to measure the resistance of each wire to ground. Also the larger the better. It should be noted that the use of a multimeter to measure the line with or without a short circuit and grounding is not accurate. Should not be, if the ground or short circuit resistance is very small, then the multimeter can be detected, if the resistance is slightly larger. Multimeter is not checked, in the 380V low voltage circuit. Should be measured with a 500V swing meter, whether between the lines or to ground. Should be above 0.38 megohm. Otherwise it is unqualified.
Multimeter test line short circuit method. First cut off the power supply of the line under test. Then the line of the control transformer, indicator, voltage transformer one end of the removal, because these components are directly across the line, if not removed, may be due to the impedance of these components to affect your measurement, some lines have inverters, rectifier bridges, and other three-phase loads, such as these devices should be detached from the circuit circuit, and then dial the multimeter to the diode file (beeping file), will be measured by the two conductive lines of the conductive
Part of the conductive part of the multimeter and the red and black pens lap, then if the multimeter has a beeping sound or display impedance, indicating that the line being tested has a problem, the normal is not called, and the table display has no digital changes. Line grounding detection method is also the same. This is just a conventional detection method, to be foolproof or to use the shaking table to detect more reliable, at least more than 0.5 megohm.
The essence of voltage is the potential difference, as long as the voltage between the two lines is 0, you can use the resistance gear measurement:
1, assuming that to measure the line A and line B between there is no short circuit, line A and line B between the zero line may have a voltage (for example, 220 volts), they are on the line of potential for the potential A and potential B, the first thing that many people think of is that, if the direct measurement of the resistance file, must be disconnected from the power supply on the line A and B, and then can be measured, this idea is not to say that the error, can only say that it is too conservative.
2, directly to the multimeter dial to AC voltage gear, select the highest range, such as AC1000 volts, and then use the multimeter AC voltage gear to measure the line A and line B, if there is a relatively high voltage between the two lines (for example, 200 volts), it can be proved that the potential A and potential B is not equal, that is, there is a difference in voltage between the potential A and the potential B, these two lines are not equipotential, these two lines are not shorted together.
3, if the line A and line B using AC voltage measurement of no voltage, in order to ensure that, and then choose a DC voltage file, such as 1000 volts to measure between them, to confirm that there is no DC voltage, this kind of proof of potential A and potential B is equal, pay attention to equal does not mean that they have no voltage on the zero line N Oh, for example, the line A and line B on the zero line N are 220 volts, but the voltage between them is also 0 volts, this time, you can use the smallest resistance gear to measure the resistance between the two lines, if close to 0 ohms, that the two lines are shorted together.
4, as for the measurement of whether the ground, simple can also be used to measure the method above, the idea is to take the ground as an ordinary line to understand. But the general measurement of whether to touch the ground, you can use a shaking table to measure the insulation resistance (generally insulated with 5 megohms), this time it is necessary to power off to measure.
