meggohm measurement

[HARRY 7]

Hello to everybody:).When we make the above measurement to compressor,what is the maximum time we leave the compressor winding under the voltage of the instrument??

[monkey spanners]

Usually just long enough for the reading to stabilise, the megger i use bleeps once it has got a reading, so 5 or 10 seconds. I believe that the test voltage should be no more than twice the normal mains supply when testing.

[HARRY 7]

Hello monkey spanners.I test to 500v DC,but the time to stabilise is much longer.

[monkey spanners]

Have you removed all the wires from the compressor terminals first?

Heres a vid i found on youtube, i think the guy is a college lecturer,

http://www.youtube.com/watch?v=1UnCicAbU8k

Heres a vid of my tester at work,

http://www.youtube.com/watch?v=hP0jnXT5SZI


Jon

[HARRY 7]

Yes i always remove the terminals but i have never heard about the time of the measurement.

[Grizzly]

Yo! Ms. good links thank you, I am sure some of the Guys will benefit!
I have exactly the same Robin Megga.
Mine does not get taken to such exotic locations though.
Cheers Grizzly

[HARRY 7]

Yes but still i cannot understand if the measurement takes about a minute,could this create a problem in the compressor or his temperature sensor?{I am referring to three phase screw compressors}

[NoNickName]

No, as long as you don't supply voltage to the thermistors. There are different megaohm meters with different preset times, the most common of which are 1, 5, 10 and 20 seconds.
Remember that compressor winding insulation must be tested with nitrogen or with refrigerant. Never under vacuum.

[mikeref]

NNN, never when on a vacuum, good point! This is so easily overlooked.

[nike123]

http://www.refrigeration-engineer.com/forums/showthread.php?t=11604

[HARRY 7]

Thanks for the manual nike!If i am reading right,the test duration is one minute.

[nike123]

Thanks for the manual nike!If i am reading right,the test duration is one minute.

Yep, for Fluke, but I don't see reason that other instruments testing time should be different if they use same method.

[HARRY 7]

To my instrument nike stabilesed after 40 seconds,so may be we are right.