Correct use of megohmmeters

Megohmmeter, also called shake meter or insulation resistance tester, is a simple, commonly used direct-reading meter for measuring high resistance, and can be used to measure the insulation resistance of circuits, motor windings, cables, and electrical equipment. There are three terminals on the megohmmeter that are marked with ground (N), circuit (U), and protection ring (G), respectively. When used, not only the wiring is correct, but also the terminal button is tightened. Also note the following:

First, the megohmmeter is to be tested for open circuit and short circuit before measurement and check if the megohmmeter is normal. The specific operation is: to open the two connecting lines, shake the handle pointer should be pointing at the infinity, then short the two connecting lines, the pointer should be at zero.

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

Third, the megohmmeter and the device under test should be connected separately with a single strand, and keep the surface of the circuit clean and dry, to avoid errors caused by poor insulation between the line.

4. During the jog test, place the megohmmeter in the horizontal position. When the handle is turned, no short circuit is allowed between the end buttons. When the capacitor and cable are shaken, the wiring must be disassembled when the crank handle is turned. Otherwise, reverse charging will damage the megohmmeter.

5. When the handle is shaken, it should be accelerated gradually and uniformly accelerated to 120r/min, and be careful to prevent electric shock. During the shaking process, when the pointer has pointed to zero, it can no longer be shaken to prevent the coil in the watch from being damaged by heat.

6. In order to prevent leakage resistance of the device under test, when the megohmmeter is used, the middle layer of the device under test (such as the inner insulation between the cable cores) should be connected to the protection ring.

7. The appropriate insulation resistance tester should be selected depending on the voltage level of the device under test. For equipment with a rated voltage below 500 volts, a 500-volt or 1000-volt megohmmeter is used. For equipment with a rated voltage of 500 volts and above, a megohmmeter of 1000-2,500 volts is used. The choice of measuring range should generally be careful not to make its measuring range exceed the insulation resistance value of the tested equipment to avoid making the reading produce a large error.

8. It is forbidden to use megohmmeter measurements at lightning weather or in the vicinity of equipment with high-voltage conductors.