What are the precautions to take when using a megohmmeter?

preparation in advance
Equipment inspection: Before using a megohmmeter, first ensure that it is working properly, including sufficient battery power (for battery driven models), flexible handle (for manual megohmmeters), correct pointer indication, and no rust or damage to the terminal posts.
Safety isolation: The tested equipment must be powered off and completely discharged, and live operation is strictly prohibited. Large equipment requires manual discharge for at least 2-3 minutes before and after measurement to ensure no residual charge.
Correct wiring
Understanding the function of terminal blocks: A megohmmeter usually has three terminal blocks: L (line), E (ground), and G (shield). The L end is connected to the tested conductor, the E end is connected to the equipment casing or ground wire, and the G end is connected to the shielding layer when necessary to reduce external interference.
On demand wiring: Connect each terminal correctly according to the measurement purpose. For example, when measuring the insulation resistance of the line to ground, connect the L terminal to the tested line and the E terminal to ground; When measuring the insulation between motor windings, connect the E end to one winding and the L end to the other winding.
Operation process
Uniform shaking: For manual megohmmeters, a constant speed of approximately 120 revolutions per minute should be maintained to ensure stable output voltage. An electric megohmmeter should be operated according to the instructions to maintain a constant voltage output.
Observation reading: After the megohmmeter pointer stabilizes, read the insulation resistance value. For devices with capacitive properties, it may take some time to wait until the capacitor is fully charged and discharged before obtaining the true reading.
Safe operation
Special person supervision: It is recommended that two people work together to complete the measurement work, one person is responsible for operating the megohmmeter, and the other person is responsible for monitoring the safety situation to ensure that no one touches the live parts during the operation process.
Body protection: Operators must wear protective equipment such as insulated gloves and insulated shoes to prevent the risk of electric shock caused by a decrease in human resistance.
Special Scene
Anti static and anti-interference: During the measurement process, avoid placing the megohmmeter and test line near high current conductors or strong magnetic field areas to reduce measurement errors.
High voltage warning: The output voltage of the megohmmeter can reach hundreds to thousands of volts. It is strictly prohibited to measure in thunderstorm weather or near high-voltage equipment.
Disposal after measurement
Discharge and reset: After the measurement is completed, regardless of the test results, the tested equipment must be fully discharged, especially for capacitor devices, which must be properly discharged.
Proper storage: When not in use or handling the megohmmeter, ensure that the instrument switch is turned off to avoid safety hazards caused by misoperation.