What is the minimum acceptable value of insulation resistance?

The rule may be stated: Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. For example, a motor rated at 2,400 volts should have a minimum insulation resistance of 2.4 megohms.
A.

What is the Megger?

Uses of Megger. The device enable us to measure electrical leakage in wire, results are very reliable as we shall be passing electric current through device while we are testing. The equipment basically use for verifying the electrical insulation level of any device such as motor, cable, generator winding, etc.
  • What is a Megger test?

    As you know good insulation has high resistance and poor insulation relatively low resistance. The Megger insulation tester is a small, portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. For good insulation, the resistance usually reads in the megohm range.
  • Why do we do Megger test?

    The megger is a device which is used to measure higher values of resistance. We uses megger to measure insulation resistance of electrical machines and cables. By measuring the insulation resistance we can find the health of insulation.
  • What is Meggering of cables?

    The following is a summary of insulation resistance (IR) testing (commonly referred to as “megger testing”) of low voltage cables (rated less than 5 kV), recognized by Nexans. Cable end condition (i.e. insulation not stripped back, cable ends not separated).
B.

What is Megger and its uses?

Megger is a measuring instrument used for the measurement of insulation resistance of an electrical system. An electrical system degrades its quality of insulation resistance with time and various environmental conditions including temperature, moisture, dust particles & humidity.
  • What is the name of the oil used in transformer?

    Insulating oil in an electrical power transformer is commonly known as Transformer Oil. It is normally obtained by fractional distillation and subsequent treatment of crude petroleum. That is why this oil is also known as Mineral Insulating Oil. Originally Answered: What is the scientific name of transformer oil?
  • What is PCB in transformer oil?

    Polychlorinated biphenyls (PCBs) are synthetic chemicals which are no longer produced in the United States, but are still found in the environment. PCBs have been used as coolants and lubricants in transformers, capacitors, and other electrical equipment because they don't burn easily and are good insulators.
  • Why is PCB harmful to the environment?

    PCBs have been used as coolants and lubricants in transformers, capacitors, and other electrical equipment because they don't burn easily and are good insulators. The manufacture of PCBs was stopped in the U.S. in 1977 because of evidence they build up in the environment and can cause harmful health effects.
C.

Why insulation resistance can not be measured by multimeter?

The reason a multimeter cannot measure such extremely high resistance is because the measurement is performed with a low voltage (often a 9V battery inside the multimeter). It does mean that an insulation resistance meter should not be used on electronic circuits.
  • How do you use a Megger tester?

    Use the Megger probes to test insulation resistance.
    1. Switch off power to the circuits you are testing.
    2. Prepare a table in which you can record the insulation values that result from your tests.
    3. Select 500 volts DC or 1000 volts DC as the test voltage on your Megger, depending on the model you are using.
  • What is the purpose of a Megger test?

    Megger is a measuring instrument used for the measurement of insulation resistance of an electrical system. An electrical system degrades its quality of insulation resistance with time and various environmental conditions including temperature, moisture, dust particles & humidity.
  • What is meant by IR value?

    1. IR Values For Electrical Apparatus & Systems
    Max.Voltage Rating Of EquipmentMegger SizeMin.IR Value
    250 Volts500 Volts25 MΩ
    600 Volts1,000 Volts100 MΩ
    5 KV2,500 Volts1,000 MΩ
    8 KV2,500 Volts2,000 MΩ

Updated: 2nd October 2019

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