back again with megger question

[mickeyrench]

First i like to thank you guys for your patients with these post.
I understand there is a rule of tumb on 1 mg for every 1000v is used as a guide line for a motor and with that value would be considered a good motor. Some of the motors I tested was 300 megs that seems like a big gap . There was one motor that tested at 5 megs which i though would be considered questionable.
Is 5 - 300 megs a big gap from bad to good?

 

[zog]

First i like to thank you guys for your patients with these post.
I understand there is a rule of tumb on 1 mg for every 1000v is used as a guide line for a motor and with that value would be considered a good motor. Some of the motors I tested was 300 megs that seems like a big gap . There was one motor that tested at 5 megs which i though would be considered questionable.
Is 5 - 300 megs a big gap from bad to good?

Hey dont ask me, I just follow the specs and get chastised for it. Rules of thumb are easy to remmember but usually not correct. AC or DC motor? When was it made? What type of windings? What was the winding temp at the time of the test? What is the size of the motor? How long was the test? All of these questions matter when tring to evaluate results.

5M is questionable but stiil OK for some motors, but not for others. Also 5M is only 2M at room temp (68 degrees F).

Dont worry so much about bad or good, a megger test is not a condition assesment test but rather a test used for trend analysis, the readings on thier own dont say much, several years of properly recorded and corrected test results are a valuable predictive maintenence tool.

Think of it like this, a Megger test, and saying good or bad is like if you went to the doctor and he had you run on a treadmill full speed for 5 minutes, if you dont die he looks at you and says, hmmm looks like you are OK, see you next year.

 

[roger]

Think of it like this, a Megger test, and saying good or bad is like if you went to the doctor and he had you run on a treadmill full speed for 5 minutes, if you dont die he looks at you and says, hmmm looks like you are OK, see you next year.

Sounds like a solid test to me, it might even mean you wouldn't need to go back for a number of years.

Following specs is fine but rules of thumb are as well.

My jack stands get my old four wheel drive up off the ground as far as I normally need to work on it, if I need it higher, I will take it somewhere that can help me with a lift.

The point is, there are different levels of testing and reporting, and for normal use, rules of thumb and information such as "A Stitch in Time" are sufficient.

Roger

 

[zog]

The point is, there are different levels of testing and reporting, and for normal use, rules of thumb and information such as "A Stitch in Time" are sufficient.

Roger

Yes, I agree, if used properly they can be, but most of the time a megger and a thumbrule will give false info to a misimformed or inexperienced user and they may be better off not doing the tests rather than do them wrong and confuse the results.

P.S. I wouldnt go to a doctor that just did that treadmill test and assumed i was in good health. I want a doctor that knows what he is doing, has the right equipment and experience for me to trust him with my life.