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.

Why is Megger important?

An instrument that is used to measure insulation resistance is a Megger. It is also known as meg-ohm-meter. It is used in several areas like multi-meters, transformers, electrical wiring, Etc. Megger device is used since the 1920s for testing various electrical devices which can measure greater than 1000meg-ohms.

Why do we Megger cables?

What is Megger Testing? Megger is an electrical instrument that is used for testing insulation resistance and machine windings to safeguard all electrical equipment from major damage.

What is an insulation tester used for?

Insulation testers use a high voltage, low current DC charge to measure the resistance within wires and motor windings to identify current leakage and faulty or damaged insulation, which can lead to arc faults, blown circuits, and risk of electrical shock or fire.

What is a bad reading on a megger?

What is a bad reading on a Megger test? If the megger reads a resistance under 1 (1,000 ohms) on your meter after the initial 60-second interval, the cable has failed and the cable should be removed. If the megger reads a resistance between 1-1.25 on your meter, then the cable passes.

Megohmmeters (Full Lecture)

Can you apply a megohmmeter to 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. ... A technician uses a hand-cranked megohmmeter to check the insulation resistance of motor windings.

How do you use insulation tester?

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 does insulation testing work?

Insulation resistance measurement is done using an IR tester. This is a portable tool that is more or less an ohmmeter with a built in generator that's used to produce a high DC voltage. The voltage usually measures at least 500V, and causes a current to flow around the surface of the insulation.

How do you test a house wiring with a Megger?

Set the megger to the lowest voltage scale and insert the test leads. Put you gloves on (rubber and leathers), hold the test leads apart and push the test button, the meter should go to full scale (air in most cases is a good insulator), that is an excellent reading.

What is a good Megger reading for wire?

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.

Why and where Megger is used?

The megger is used to measure a high quantity of insulation resistance. ... Infinity resistance means that it is too high for the instrument to measure. If the test leads are connected to each other while the hand crank is turned, the pointer will defect to zero, indicating no resistance between the test leads.

What does a Megger test tell you?

The Megger test is a method of testing making use of an insulation tester resistance meter that will help to verify the condition of electrical insulation. ... The IR gives a measure of the enduring power of an insulator to bear the service voltage without any current leakage path.

What causes low insulation resistance readings?

Low insulation resistance may be due to the age of the installation, or alternatively it may be caused by an individual circuit, which would merit further investigation. In summary, insulation resistance testing should be undertaken at relevant times during and on completion of an installation.

What affects insulation resistance?

Factors that affect insulation resistance measurements include such things as temperature, humidity, previous conditioning, test voltage, charging current and duration of the test voltage (electrification time).

What is a good insulation resistance reading?

Insulation resistance should be approximately one megohm for each 1,000 volts of operating voltage, with a minimum value of one megohm. ... In practice, megohm readings normally are considerably above this minimum value in new equipment or when insulation is in good condition.

What is the difference between an earth leakage test and an insulation resistance test?

Earth leakage tests are often performed in place of an insulation test if there is doubt an insulation test could damage the equipment under test. This measures the difference in current between the live and neutral conductors. The difference is displayed as the leakage current.

How megger works for testing?

Testing voltage is produced by electromagnetic induction in case of hand-operated megger and by a battery in case of electronic type megger. The deflection of pointer increases with the increases in voltage in the external circuit and also decreases with the increase in current.

Can a megger damage a motor?

Any megger with a higher voltage output than 500 volts DC should be used by an experienced technician. A high voltage for too long of a time may further weaken or fail motor windings and the winding insulation could be damaged by the testing procedure.