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.
What is an acceptable reading for insulation resistance?
The rule states that insulation resistance should be approximately one megohm for each 1000 volts of operating voltage, with a one megohm minimum. (By following this rule, a motor rated at 2400 volts should have a minimum insulation resistance of 2.4 megohms).
What is infinity on a Megger?
If your megohmmeter is reading “OL” (over load) or “I” (infinity), these are commonly used readings on megohmmeters when the measurement exceeds the maximum indicated value of the tester.
Is a Megger AC or DC?
If we apply DC voltage then as we know Capacitor blocks the flow of DC, only leakage current due to imperfection of insulator will flow and hence the Resistance measured by Megger will actually represent Insulation Resistance. This is the reason, an Insulation Tester or Megger have DC voltage generator.
What does Megging a wire mean?
A megger is also known simply as an insulation tester. It’s basically an ohmmeter, but it’s one that generates its own electricity under high DC voltages, such as 500 and 1,000 volts, and transmits it in small currents through the cable to be tested. The voltages are high, but the currents are small enough to be safe.
What is the minimum acceptable insulation resistance for a Class 2 appliance?
Adequate insulation is defined as greater than 1 M ohm for Class I appliances and 2 M ohm for Class II appliances.
How do you use 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.
What you will determine in insulation testing?
An insulation resistance (IR) test measures the total resistance between any two points separated by electrical insulation. The test, therefore, determines how effective the dielectric (insulation) is in resisting the flow of electrical current.
What is a good Megger reading for a 480V motor?
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.
What does a reading of 0 ohms mean?
Resistance, symbolized by the (Ω) symbol and measured in Ohms, is a measurement of how well a current can travel through a circuit or a given path. A circuit with no resistance (0) would indicate a complete circuit, or one that has no short.
What is a mega 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 is the difference between earth Megger and insulation Megger?
An insulation tester performs the basic measuring function a megohmmeter does—measuring very high resistance values by sending a high voltage signal into the object being tested—and it often does much more; it usually performs more functions, including more complex testing and recording of measurements.
