Testing compressor winding insulation with megger.

[xchcui]

Hello.

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?

Thanks.

 

[xchcui]

Anyone?

 

[aap2]

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

 

[panter]

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

 

[xchcui]

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.