Leakage Measurement Methods and Notes for Digital Multimeters
Generally, use the AC voltage range to measure the equipment's voltage to ground. With power disconnected, use the resistance range to measure the resistance to ground of live parts.
For severe electric leakage faults, they can be detected with the multimeter's resistance range. However, mild leakage cannot be measured by a multimeter. An insulation resistance tester, such as a hand-cranked megohmmeter or digital megohmmeter, can be used for insulation measurement. These instruments can simulate the actual operating voltage, while the test voltage of a multimeter is very low.
First ask the reporting user about fault phenomena and obvious symptoms observed. Then visually inspect for visible fault points before carrying out further checks.
① Disconnect the main isolating switch of the user's power incoming line and turn off all electrical loads, such as unplugging the refrigerator and switching off water pumps.
② Set the digital multimeter to the 200MΩ resistance range. Place one test lead on one of the two outgoing wires on the load side, and touch the other test lead to the wall, preferably the protective earth wire or a temporary earth wire. Wait until the reading on the multimeter stabilizes, then record the insulation resistance value of the main circuit. If the insulation resistance is less than 0.5 MΩ, there is a fault in the main circuit. If the insulation resistance is above 0.5 MΩ, the main circuit can be ruled out as the source of the fault. Measure the other wire in the same way and check the reading to verify whether the main circuit is faulty.
③ Check the insulation resistance of branch circuits and each electrical appliance. Test them one by one using the same method until the fault point is located.
Precautions for Measuring Leakage with a Digital Multimeter
① When using the 200MΩ resistance range of the multimeter, do not touch the metal part of the test leads during measurement, otherwise inaccurate readings will occur.
② Discharge all electrical equipment before measurement to prevent injury from capacitive current stored in the equipment.
This method can locate fault points under power-off conditions and is also suitable for leakage detection for power consumers and factory workshops. Note that when searching for leakage faults, the power incoming line and neutral wire must be disconnected to prevent electric shock accidents.
