1. Selection of insulation resistance tester:

It is stipulated that the voltage level of the insulation resistance tester should be higher than the insulation voltage level of the tested object. Therefore, when measuring the insulation resistance of equipment or lines with a rated voltage below 500V, a 500V or 1000V megohmmeter can be used;

When measuring the insulation resistance of equipment or lines with a rated voltage above 500V, 1000~2500V megohmmeter should be used; when measuring insulators, 2500~5000V megohmmeter should be used.

Generally, a megger with a range of 0~200MΩ can be used to measure the insulation resistance of low-voltage electrical equipment.

2. Measuring method of insulation resistance tester:

The megohmmeter has three terminals. The two larger terminals at the upper end are marked with "Earth" (E) and "Line" (L) respectively, and the smaller terminal at the bottom is marked with "Protection ring" ( Or "shield") (G).

1) Insulation resistance of the line to the ground

Connect the "grounding" terminal (ie E terminal) of the megohmmeter to the ground reliably (usually connected to a certain grounding body), and connect the "line" terminal (ie L terminal) to the tested circuit, as follows As shown in the figure.

After connecting, shake the megohmmeter clockwise, the speed gradually increases, keep it at about 120 rpm and then shake at a constant speed. When the speed is stable and the pointer of the meter is also stable, the value indicated by the pointer is the insulation resistance of the measured object. value.

In actual use, the two terminals E and L can also be connected arbitrarily, that is, E can be connected to the measured object, and L can be connected to the grounding body (that is, grounding), but the G terminal must not be connected wrongly.

Note: (a) measure the insulation resistance of the line; (b) measure the insulation resistance of the motor; (c) measure the insulation resistance of the cable.

2) Measure the insulation resistance of the motor

Connect the E terminal of the megohmmeter to the chassis (that is, grounding), and the L terminal to the winding of a certain phase of the motor. As shown in the figure above, the measured insulation resistance value is the insulation resistance value of a certain phase to the ground.

3) Measure the insulation resistance of the cable

When measuring the insulation resistance between the conductive core of the cable and the cable shell, connect the terminal E with the cable shell, connect the terminal L with the core, and connect the terminal G with the insulating layer between the cable shell and the core at the same time.