The digital megohmmeter has three binding posts: one is "L", one is "E", and the other is "G" (shielded). When measuring the insulation resistance of power lines or lighting lines, "L" is connected to the line to be tested, 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, you must first cut off the power supply. When encountering capacitive equipment, such as cables, the line must first be discharged.

2. When using the digital megohmmeter, 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 "L" and "E" terminals, and slowly turn the handle of the megohmmeter. Check to see if the pointer is at "zero".

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

5. When measuring with a digital megohmmeter, the reading after one minute of rotation shall prevail.

6. When measuring, the revolutions of the megohmmeter should reach 120 revolutions per minute.

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