The rule may be stated: 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 is the acceptable Megger reading for a DC motor?
A general rule-of-thumb is
10 Megohm or more
.
This is how the test works: DC voltage of 500 or 1000 V is applied between the windings and the ground of the motor.
What is an acceptable 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 insulation resistance of a motor?
It is recommended that the insulation resistance of the motor should at least be
1 MΩ
1
)
, and for the voltage to ground of 200 V, I0r should be 200 μA or below.
What is a good Megger reading for a 480v motor?
Our minimum meg readings are 1.5 megs for 480 volt motors at 1000 volt meg. (That would be 1.5 million ohms to ground resistance.) 1.5 to 20 is fair.
20 to 50 is good
.
What is a bad Megger reading?
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.
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. For example, a motor rated at 2,400 volts should have a minimum insulation resistance of 2.4 megohms.
How do you read a megger?
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. Any reading above 1.25 is considered excellent.
Why megger test is done?
Megger testing
measures resistance between the phase windings of the motor under test and ground
. If there is an insulation breakdown, the resistance is negatively impacted and there is a departure between phases or between one measurement and a previous one and a determination of motor health is made.
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.
What is the resistance of a motor winding?
The reading should be
between 0.3 to 2 ohms
. If it is 0, there is a short. If it is over 2 ohms or infinite, there is an open. You can also dry the connector and retest to possibly get more accurate results.
How is motor resistance calculated?
Ohm's law tells you that current through a wire – even a long wire wound around a motor solenoid – is equal to the voltage divided by the resistance. You can determine the resistance of a motor coil if you know the wire gauge,
the radius of the solenoid and the number of windings
.
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.
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.
