When is the shielding end used?

There are three terminals of the megohmmeter: high-voltage terminal, ground terminal, and shielding terminal. Generally, the measured insulation resistance is connected between the “high-voltage terminal” and the “ground terminal” for measurement, but when the surface leakage of the measured insulator is serious, The shielding ring of the measured object or the part that does not need to be measured must be connected to the "shielding" end, so that the leakage current flows directly back to the negative terminal of the megohmmeter through the shielding end to form a loop, which fundamentally eliminates surface leakage The effect of current, the shielding end is connected to the megohmmeter because when the measured object is not clean and damp, the surface leakage current is generated. Connecting the shielding wire to the megohmmeter can reduce the measurement error and make the measured insulation resistance value. accurate.

Case of megohmmeter connected to shielded end

It should be especially noted that when measuring the insulation resistance between the cable core and the outer surface, the shielding end must be connected, because when the air humidity is high or the cable insulation surface is not clean, the leakage current on the surface will be very large. In order to prevent For the influence of the measured object on its internal insulation measurement due to leakage, generally a metal shielding ring is added to the outer surface of the cable core and connected to the "shielding" end of the megohmmeter.