Megohmmeters provide a quick and easy way to determine the condition of the insulation on wire, generators, and motor windings. A megohmmeter is an electric meter that measures very high resistance values by sending a high voltage signal into the object being tested.
How does a megohmmeter differ from an ohmmeter?
The chief advantage of the megger over an ohmmeter is its capacity to measure resistance with a high potential or breakdown voltage. Impedence of insulation is very high. A megger is specifically designed to accurately measure high impedences. An ordinary multimeter is designed to measure lower, more finite impedences.
What does it mean to megger test?
Megger testing is an electrical test of insulation performance in an electrical apparatus. A mega-ohm meter is applied to each phase connection for the motor leads and ground, and a voltage applied.
What are good megohmmeter readings?
Anything reading between 2 megohms and 1000 megohms is usually considered a good reading, unless other problems have been noted. Anything less than 2 megohms indicates an insulation problem.
How do you test a house wiring with a megger?
If you are testing insulation resistance to ground, place the positive probe on the ground wire or the grounded metal junction box and the negative probe on the conductor or terminal. Energize the Megger for 1 minute. Read the value of the resistance at the end of the minute test and note it in your table.
How megger works for testing?
Megger works on the principle of electromagnetic attraction. When a primary coil that is carrying current is placed under the vicinity of a magnetic field it experiences a force. This kind of force generates a torque that is made to deflect the pointer of the device which gives some reading.
Can you use a megohmmeter on electronics?
Megohmmeter measurements can now be more accurate, rapid and safer than ever before. A considerable number of electronics personnel working throughout the electrical industry are military trained. And many of them learned on a simple hand-cranked analog meter, properly termed a megohmmeter, or insulation tester.
What does a high ohm reading mean?
Higher numbers indicate a higher resistance rating, which means more energy will be required to integrate the component in a circuit. When you test a resistor, capacitor, or another electronic component, the ohmmeter will display a number indicating its resistance.
What causes low Megger readings?
Two conductors have consistently lower values: Because the conductors adjacent to the ground conductor only have one layer of insulation, those conductors will have lower insulation resistance and the Megger values will be lower.
What should a 480V motor Meg?
IEEE recommends that for motor starting that the operational voltage, expressed as a meg-ohm value doubled plus 1000 is the minimum meg value for starting. For a 480V motor that would mean . 480Meg x 2= . 960 Meg + 1000, so a minimum ground resistance for starting a 480V is 1.960 Meg or round up to 2 meg-ohms.
How long do you hold the test button on a Megger?
With hand-cranked Megger instruments, it’s a lot easier for you to run the test for only 60 seconds, taking your first reading at 30 seconds. If you have a line-operated Megger instrument, you’ll get best results by running the test 10 minutes, taking readings at 1- and at 10-minutes, to get the polarization index.
How does a Megger find earth resistance?
To measure the earth resistance with a megger earth tester, the earth electrode under test is connected to its E terminal and P and C terminals are connected to auxiliary electrodes through a connecting lead of negligible resistance.
