Insulation resistance requires the use of megohmmeters of different grades according to the rated voltage of the appliance being tested (see attached diagram). The megohmmeter has three terminals: one for "L", one for "E", and one for "L". One for the "E", there is a "G," (shielding), the measurement of insulation resistance of power lines or lighting lines, "L" connected to the line under test, "E" wiring. Measurement of insulation resistance of the cable, in order to make the measurement results accurate, to eliminate the core insulation surface leakage caused by the measurement error, should also be "G" to the cable insulation paper. To note the following, the measurement of insulation resistance of electrical equipment, you must first cut off the power supply, meet the capacitive nature of the equipment, such as cables, lines must first be discharged .......