Quick Answer: What Is A Bad Insulation Resistance Reading?

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 do you test an insulation resistance on a motor?

To measure insulation resistance, a DC voltage of 500V or 1000V is applied between the windings and the ground of the motor as shown below: During the measurement and immediately afterwards, do not touch any terminals of the motor as some of them carry dangerous voltages that may be fatal.

What is the minimum acceptable value of insulation resistance for a SELV circuit?

0.5 MΩbetween the live conductors of each SELV circuit and Earth (Fig 1 shows an example). A minimum measured IR value of 0.5 MΩ is considered satisfactory for these 250 V tests (Regulation 612.3.

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.

How do you test Megger Insulation Resistance?

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 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.

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 the acceptable earth resistance value?

5.0 ohmsIdeally a ground should be of zero ohms resistance. There is not one standard ground resistance threshold that is recognized by all agencies. However, the NFPA and IEEE have recommended a ground resistance value of 5.0 ohms or less.

What is an acceptable 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 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.

Can you test insulation resistance with a multimeter?

An insulation resistance meter can measure into the gigohm or hundreds of gigohm range; some models reach into tera-ohms! 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).

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

What is considered a bad Megger reading?

Turn on and read the meter. 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 the minimum permitted insulation resistance of live to Earth?

1 MΩ(The term ‘Earth’ means that the protective conductor(s) are connected to the earthing arrangement.) Perform 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.

What does an 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.

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.

What is insulation resistance of motor?

Insulation Resistance (IR) is among the most common motor tests. … In an IR or megohm test the voltage applied and the total leakage current are measured between the windings and the motor frame/ground. Ohms law is applied to calculate the resistance in megohms.