How to use a Megger Insulation Tester?
A megger also known as a megohmmeter employs high voltage to assess the insulation strength of wires. A megohm equals 1,000,000 Ω of resistance.
This high resistance measurement assures the wire’s insulation is intact throughout its length.
To measure the high resistance value a high voltage is applied to the wire conductor in certain cases up to 15,000 V.
Most battery-powered meggers produce a voltage ranging from 1000 to 3000 V.
Equipments Required
- Electrical hand tools
- Plastic wire nuts.
Step-by-Step Procedure to use Megger
Step 1
Turn off all electrical power to the cable being examined.
Use the proper electrical hand tools to disconnect the wires from any part of the circuit.
Due to the intricacy of some electrical circuits, multiple instruments can be necessary to isolate the wire that has to be tested.
Step 2
Remove all electrical connections from the wire.
Make both ends of the cable visible by showing the bare copper connection point.
Seal one end of wire’s copper connector with a wire nut.
This will prevent the conductor from accidently shorting to ground and producing an incorrect reading.
Step 3
Connect the positive (+) end of the megohmmeter to the bare copper connection on wire being tested.
Connect the meter’s ground wire to the metal ground of electrical system. Typically, this location will be the metal conduit (or) the main electrical box.
Step 4
Switch the meter to “on” position.
Most megohmmeters have a charging button on the face of the meter.
Press the charging button and check the meter.
It usually takes 3 to 5 seconds for meter to charge the wire to its maximum voltage.
Step 5
Read the meter. A meter reading of greater than (>) 999 meg indicates a completely insulated line.
A value (<) 1.00 meg may suggest a wire issue.
A reading via these 2 resistances will usually work without any difficulties in the electrical circuit.
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