Digital megohmmeters have three binding posts: one for "L", one for "E", and one for "G" (shield). When measuring the insulation resistance of power lines or lighting lines, "L" is connected to the line under test, and "E" is grounded. When measuring the insulation resistance of the cable, in order to make the measurement result accurate and eliminate the measurement error caused by the leakage of the surface of the core insulation layer, "G" should also be connected to the insulation paper of the cable.

Pay attention to the following points when measuring:

1. To measure the insulation resistance of electrical equipment, the power supply must be cut off first. When encountering equipment with capacitive properties, such as cables, the line must be discharged first.

2. When using the digital megger, it must be placed flat.

3. Before using the digital megohmmeter, turn it a few times to see if the pointer is at the maximum position, then short-circuit the two terminals "L" and "E", and slowly turn the handle of the megohmmeter. See if the pointer is at "zero".

4. The leads of the digital megger must be well insulated, and the two wires should not be twisted together.

5. When measuring the digital megger, the reading after one minute of rotation shall prevail.

6. When measuring, the speed of the megohmmeter should reach 120 rpm.

7. The range of digital megohmmeters is often several gigaohms, and the minimum scale is about 1 megohm, so it is not suitable for measuring resistances below 100 kiloohms.