Quick Answer: How Do You Test A Megger?

What is a bad Megger reading on a motor?

This is how the test works: DC voltage of 500 or 1000 V is applied between the windings and the ground of the motor….A general rule-of-thumb is 10 Megohm or more.Insulation resistance valueInsulation level2 Megohm or lessBad2-5 MegohmCritical5-10 MegohmAbnormal10-50 MegohmGood2 more rows•Jun 9, 2014.

What is infinity in Megger?

When the pointer of the PMMC instrument deflects towards infinity, it means that the voltage coil remains in the weak magnetic field and thus experienced the very little torque. The torque experienced by the coil increases when it moves insides the strong magnetic field.

What reading should you get for insulation resistance?

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 insulation resistance?

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 bad insulation resistance reading?

The purpose of the IR test is to check for damaged insulation, this can be mechanical damage or damage by heat, (overloaded cables), readings less than 2 Mohm indicate damaged insulation, readings of 2-50 Mohm are indicative of long circuit lengths, moisture and contamination and do not indicate the insulation quality, …

How do I test my cable for Megger Insulation?

Clamp the alligator clip on one of the megger probes to the wire or cable, touch the other probe to the exposed conductor and press the test button. The megger will generate a current between the probes, and the meter will record the resistance of the jacket to the flow of the current.

How can I increase my Megger value?

Example-1: For 11KV, Three Phase Motor. IR Value =0.415+1=1.41 MΩ but as per IEEE43 It should be 5 MΩ….IR Value of Motor as per NETA ATS 2007. Section 7.15.1.Motor Name Plate (V)Test VoltageMin IR Value1000V1000V DC100MΩ2500V1000V DC500MΩ5000V2500V DC1000MΩ8000V2500V DC2000MΩ5 more rows•Apr 29, 2012

Why do you Megger a motor?

It specifically tests the motor windings insulation. Depending on the insulation class of the motor, a good motor could measure well into Tera Ohms or 1,000,000,000,000 ohms! This is an insulation test of motor windings, commonly referred to as megging, to megger, or to meg a motor.

Is Megger testing dangerous?

Although Megger insulation testers are NOT inherently dangerous, safety officers and safety S.O.P.s often call for added diligence above 500 V. Time is an important test variable in insulation testing, much more so than in many familiar electrical tests.

How do I test my alternator for insulation resistance?

This test involves using a Megger type instrument that can be set to apply the test voltage to the winding twice in a period of ten minutes. Usually, a motorised Megger is used. The value of the windings IR is recorded after 1 minute of the motorised Megger test and then again after 10 minutes.

How many ohms should a motor read?

0.5 ohmsEarth Continuity and Resistance Test A good motor should read less than 0.5 ohms. Any value greater 0.5 ohms indicate trouble with the motor.

How do you calculate insulation resistance?

If we apply a voltage across a resistor and then measured the consequential current flow, we can then use the formula R=U/I, (where U=Voltage, I=Current and R=Resistance) to calculate the resistance of the insulation.

How Megger test is done?

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. Insulation resistance quality of an electrical system degrades with time, environment condition i.e. temperature, humidity, moisture and dust particles.

What is a good reading on a Megger?

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 perform an insulation resistance test?

After the connections are made, the IR test is done at a low voltage, say 500V. The test specimen then is discharged and the test is done again, this time at a higher voltage, say 2500V. If more than a 25% difference exists between the two IR readings, age deterioration or damaged insulation should be suspected.

Can a Megger kill you?

The megger supplies over 500 volts, and that is enough to give a fatal shock.

What does a 0 reading on an ohmmeter mean?

Ohmmeter is an instrument used for measuring resistance of a component or a circuit. Resistance is measured in ohms with no current flowing through the circuit. … It indicates zero ohms when there is no resistance between the test points. This shows continuity of current flow in a closed circuit.

What is the lowest acceptable insulation resistance for a cable?

1 MΩPerform the insulation resistance test between conductors at a reduced test voltage of 250 V DC. However, where this option is used, the minimum acceptable insulation resistance remains 1 MΩ.

How do you find the insulation resistance of a 3 phase motor?

Phase Resistance: Take the insulation tester and set it to 500V. Take each end and place it on different permutations of L1, L2 and L3 and record each reading. Phase to Earth Resistance: Take the insulation tester, using the same setting, and check each lead from phase to the frame of the motor.

What are the factors that affect the insulation resistance?

The factors that commonly affect the insulation resistance are:Surface condition. For example oil or carbon dust on the equipment’s surface that can lower the insulation resistance.Moisture. … Temperature.Feb 11, 2015