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How to use megohm meter correctly

time:2020/7/6   source:华天电力  reading:986 time

Megohmmeter is also called shaking table or insulation resistance tester. It is a simple and commonly used direct reading instrument for measuring high resistance. It can be used to measure the insulation resistance of circuits, motor windings, cables, and electrical equipment. There are three terminals marked with ground (N), circuit (U), and protective ring (G) on the megohmmeter. When using, not only must the wiring be correct, the terminal button should be tightened, but also pay attention to the following matters:

Insulation Resistance Tester.png

 1. Before the measurement, conduct an open circuit and short circuit test on the megohmmeter to check whether the megohmmeter is normal. The specific operation is: open the two connecting wires, shake the handle pointer to point to infinity, and then short the two connecting wires, the pointer should point to zero.

 2. The device under test must be disconnected from other power sources. After the measurement, the device under test must be fully discharged (about 2 to 3 minutes) to protect the device and personal safety.

 3. The single-strand wire should be used for separate connection between the megger and the device under test, and keep the surface of the circuit clean and dry to avoid errors caused by poor insulation between the wires.

 4. When shaking, put the megohmmeter in the horizontal position, and there is no short circuit between the end buttons when the crank is turned. When shaking the capacitor and cable, the wiring must be disconnected when the crank is turned, otherwise the reverse charging will damage the megohmmeter.

Fifth, when shaking the handle, it should be slow to fast, evenly accelerate to 120r/min, and pay attention to prevent electric shock. During the shaking process, when the pointer appears to be zero, it can no longer continue to prevent the coil in the watch from being damaged by heat.

6. In order to prevent the leakage resistance on the surface of the device under test, when using a megohmmeter, the middle layer of the device under test (such as the inner insulation between the cable shell cores) should be connected to the protective ring.

7. The appropriate insulation resistance tester should be selected depending on the voltage level of the equipment under test. For devices with a rated voltage below 500 volts, choose a 500 volt or 1000 volt megohmmeter; for devices with a rated voltage of 500 volts and above, choose a 1000 to 2500 volt megohmmeter. The selection of the measuring range should generally be careful not to make the measuring range too much exceed the insulation resistance value of the tested equipment, so as not to cause a large error in the reading.

8. It is forbidden to use megohmmeter to measure in lightning weather or near equipment with high-voltage conductors.

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