Motor Insulation Resistance Test Values

Curve a shows test values as measured.

Motor insulation resistance test values.

Set the voltage. Also acceptable values of insulation resistance depend upon the equipment you re testing. For a 440v motor minimum ir between phase and ground 440 1000 1 1 44 megohm example 2. For 11kv equipment mi.

Set the voltage level of the insulation resistance tester to 500v. Figure 4 typical record of insulation resistance of a mill motor. The measurement of insulation resistance is carried out by means of a megohmmeter high resistance range ohmmeter this is how the test works. 3 shows a typical scale which reads increasing resistance values from left up to infinity or a resistance too high to be measured.

Ansi neta mts 2015 table 100 11 insulation resistance test values rotating machinery for one minute at 40 c. A general rule of thumb is 10 megohm or more. Minimum ir in megohm kv 1 example 1. Curve b shows same values corrected to 20 c see page 22 giving a definite downward.

Hands down without a doubt one of the most universally searched topics on ec m s website from a historical perspective is insulation resistance testing as a result some of our most popular evergreen articles like understanding insulation resistance testing continue to top the charts when it comes to most popular content. Values based on ieee std 43 2013. Check the motor frame earth from phase to phase u to e v to e w to e. B kv is the rated machine terminal to terminal voltage.

Dc voltage of 500 or 1000 v is applied between the windings and the ground of the motor. The insulation system of an electrical motor is said to be in good condition if. Check full load amps flas with the appropriate meter when the motor is turned on or with a full preference. Ground insulation test of a motor.

The international electrical testing association neta specification maintenance testing specifications for electrical power distribution equipment and. Historically many field electricians use the somewhat arbitrary standard of 1 megohm per kv. Insulation resistance test insulation resistance failure of an electric motor is one of the first signs that the motor is about to fail. Determine rules for the actual minimum insulation resistance value of an electric motor because resistance varies according to method of construction condition of insulation material used rated voltage size and type.

During the measurement and immediately afterwards some of the terminals carry dangerous voltages and must not be touched. The minimum test value of motor insulation resistance is 1 meg ohm 1 mh. A rated line to line voltage for three phase ac machines line to ground voltage for single phase machines and rated direct voltage for dc machines or field windings. Minimum insulation resistance ir value is depend upon rated line voltage of equipment.

For a three phase motor insulation resistance is usually measured between each motor winding or phase and between each motor phase and motor frame earth using an insulation tester or megger.