By hvhipot 
How to use high-voltage megohmmeter:
1. Before measurement, perform 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 and the pointer should point to infinity, and then short-circuit the two connecting wires, the pointer should point to zero.
2. The equipment under test must be disconnected from other power series resonances. After the measurement, the equipment under test must be fully discharged (it takes about 2 to 3 minutes) to protect the equipment and personal safety.
3. Single-stranded wires should be used to connect the megger and the device under test separately, and the surface of the circuit should be kept clean and dry to avoid errors caused by poor insulation between the wires.
4. During panning, place the megger in a horizontal position, and no short circuit between the end buttons is allowed when the crank is rotating. When testing capacitors and cables, the wiring must be disconnected when the crank is turned, otherwise the megohmmeter will be damaged by reverse charging.
5. When shaking the handle, it should be slower and faster, and evenly accelerate to 120r/min, and pay attention to prevent electric shock. During the shaking of the high-voltage megohmmeter, when the pointer has reached zero, it can no longer continue to shake to prevent heating and damage to the coil in the meter.
6. In order to prevent the surface leakage resistance 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 core) should be connected to the protective ring.
7. The appropriate insulation resistance tester should be selected according to the voltage level of the equipment under test. Generally, equipment with a rated voltage below 500 volts should use a 500 volt or 1000 volt megohmmeter; for equipment with a rated voltage of 500 volts and above, a 1000-2500 volt megger should be used. In the selection of the measuring range of the high-voltage megohmmeter, care should be taken not to make the measurement range excessively exceed the insulation resistance value of the tested equipment, so as to avoid large errors in the readings.
8. It is forbidden to use a megohmmeter to measure in lightning weather or near equipment with high-voltage conductors.