Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here


Testing compressor winding insulation with megger.

Testing compressor winding insulation with megger.

Testing compressor winding insulation with megger.


I test an air conditioner's compressor 3.5HP with megger(500V) and i got a result,0.5MΩ.
Good results should be above 50MΩ-100MΩ,while the result that i got is very low.
The compressor is working very good and the current consumption is normal.So,i wonder if i did something wrong which gave me an error result.
Before i took the measurment,i disconnected the three wires from the compressor pins(C/R/S).
One probe i connected to one of the pins and since there wasn't any bare metal on the compressor body to connect the second probe,
i connected the second probe to the metal sqaure box which is located above the compressor(the metal box that contains the capacitors,the contactor etc.).
The compressor's body and the metal box are both grounded as the whole body of the outer unit,so i assumed that it will be the same.
But as i mention above i got a very low result 0.5MΩ and i would like to know:
Could it be that i got very low result since the megger,actually,measured something else or was influenced from something else due to a wrong measurment procedure?Or maybe i had to disconnect some more component before the testing?


RE: Testing compressor winding insulation with megger.


RE: Testing compressor winding insulation with megger.

Connect your probes across the C/R/S leads. That should give you a better result.

God made the integers, all else is the work of man. - Leopold Kroenecker

RE: Testing compressor winding insulation with megger.

0'5 MOhm is not bad result for 380V motor . Our standard is 1KOhm per volt like minimum value for motor insulation .
Good luck

RE: Testing compressor winding insulation with megger.

The compressor voltage,btw,is 220V.So,i guess that even a lower minimum value is acceptable(compare to the 380v motor).

Thanks alot for your help.smile

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close