Quick Answer: What Is Considered A Bad Megger Reading?

How do you Megger a 3 phase motor?

Turn off the power supply to the motor, usually accomplished by switching the circuit breaker.

Place one megger probe to the any mounting bolt on the breaker box to test for grounding continuity, then touch the other probe to a motor terminal.Crank the handle for about a minute, and notice the resistance reading.More items….

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

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 does a Megger work?

Definition: The Megger is the instrument uses for measuring the resistance of the insulation. It works on the principle of comparison, i.e., the resistance of the insulation is compared with the known value of resistance. … The accuracy of the Megger is high as compared to other instruments.

Can you Megger a lighting circuit?

As long as the selected megger output voltage is no higher than the peak voltage of the normal AC source you could probably get away with it. Meggering at higher voltages risks destruction of the LED driver circuits, if not the LEDs themselves.

What is the acceptable voltage between neutral and earth?

110 voltNeutral-to-earth voltage (N-E), sometimes called “stray voltage,” is a condition that results when an electrical current flows through a neutral conductor. Most (110 volt) electric lines contain three wires- one “hot” or powered, one neutral and the ground wire.

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, …

What is the minimum acceptable value of insulation resistance?

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.

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.

How do you test a Megger?

Select 500 volts DC or 1000 volts DC as the test voltage on your Megger, depending on the model you are using. Check whether your model has an integrated voltage tester for live circuits. If it doesn’t, check the circuits to be tested with a voltage tester to make sure they are not live.

What does insulation resistance test prove?

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.

Is insulation resistance a dead Test?

Insulation Resistance Test (dead test) Repeat the procedure between the live and earth, and the neutral and earth. Notes: Neon’s will cause false readings, as will emergency or discharge lighting, so ensure these are all disconnected prior to commencing tests.

What is a good motor Megger reading?

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 level5-10 MegohmAbnormal10-50 MegohmGood50-100 MegohmVery good100 Megohm or moreExcellent2 more rows•Jun 9, 2014

Can a Megger kill you?

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

Is a Megger AC or DC?

Megger is an instrument used for measuring insulation resistance of a cable, but the cable that is to be tested is used in AC lines and the megger uses DC as the testing voltage.

How do you calculate insulation resistance?

How is insulation resistance calculated and tested? We should all be familiar with Ohm’s law. 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.