How to Use a Megohmmeter ?
Meggers generate voltage to determine the high resistance value of insulation. Typically, the smallest value that a megohmmeter can supply is 1,000 volts, while some hand-crank meggers can supply as much as 10,000 volts or more through a small generator inside the meter. To run a megger test, follow these steps
Step 1. Cut power
Make sure you eliminate any voltage running through the wires you want to test.
Step 2. Uninstall wires
Disconnect the wires you want to test from both ends of the circuit and all feeding wires in motors.
Step 3. Connect the ground lead
Connect one of the megger’s leads to a ground connection such as the wire insulation, the electrical frame, or the ground.
Step 4. Connect to conductor
Connect the other megger lead to the conductor such as the exposed copper of the wire or motor terminal.
Step 5. Build voltage
Crank the generator handle to build voltage. This could take anywhere from two to five seconds.
Step 6. Read meter
Determining a safe reading depends on what you’re testing. Generally, a reading should equal one megohm for each 1,000 volts of operating voltage. For a motor that has a 1,500 operating voltage, a perfect reading would be 1.5 megohms. A minimum reading should never be less than one megohm.
If the insulation resistance value is high. if 440 volts motor has an IR value of more than 1 Mega-ohm and above, it means motor winding insulation is good.
Step 7. Complete testing
Complete testing of remaining wires or terminals.
After the megger test of the motor, We must connect the winding to the earth in order to discharge the build-up voltage of the winding.