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the winding sensor short out if megged in a vac,also for what a CCH on the screws is even with Yorks Hellicals. if they are stone cold you will read a shorted winding to ground,and have had then tripped the unit mounted breakers during winters.

LOL!!!!!!!!!!!!!

i will post it

Originally Posted by jayguy

i meg everything at 1000 VDC...even 115 VAC motors...no problems. i have also megged motors in 500 micron vacuums without issue...my megger tops out at 0.002 ADC...not gonna hurt anything.

applying line voltage to a motor in a deep vacuum...now that's a youtube video I want to see!

Originally Posted by supertek65

you should set the voltage at twice the rated voltage,
I almost exclusively work on 480 stuff
i always meg at 1000 volts.

i meg everything at 1000 VDC...even 115 VAC motors...no problems. i have also megged motors in 500 micron vacuums without issue...my megger tops out at 0.002 ADC...not gonna hurt anything.

applying line voltage to a motor in a deep vacuum...now that's a youtube video I want to see!

you should set the voltage at twice the rated voltage,
I almost exclusively work on 480 stuff
i always meg at 1000 volts.

Originally Posted by R123

Mlk, after researching this, you are right about not to meg at a much higher voltage than the voltage rating of the motor.

Mlk, after researching this, you are right about not to meg at a much higher voltage than the voltage rating of the motor.

Originally Posted by mlkwal1

Well I can try, haha
I know for a fact that not supposed to meg n a vac
As far as my example : we'll that may be wrong example.,
Guess what I was trying to say was if you compressor motor volt rating is 600 volt, not supposed to meg at a higher voltage., am I correct in typing this??

You are correct that you are not supposed to meg in a DEEP vacuum but I've never heard about not to meg at a higher voltage. As a matter of fact, my megged doesn't go below 500 volts and I meg 230 volt motors all the time.

It`s not the voltage that kills a motor. It`s always the current. I haven`t seen an compressor motor killed by megging him. But most compressor manufacturers recommend not to megger with a system in deep vacuum.

Originally Posted by R123

What??????

Can you please enlighten us on this????

Well I can try, haha
I know for a fact that not supposed to meg n a vac
As far as my example : we'll that may be wrong example.,
Guess what I was trying to say was if you compressor motor volt rating is 600 volt, not supposed to meg at a higher voltage., am I correct in typing this??

You can get a bad meg reading on a good rtaa screw compressor. If the compressor has the old style terminals and is rusty under the motor terminals insulators. I have had them go as low a .5 megaohms.

Yes you can and what were the megger readings???? Was the one tripping the breaker grounded, or pulling LRA?


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The same rules apply as to any other motor. But with an RTAC you will probably see lower readings than you would expect. I suspect that has more to do with the POE oil than it does with the motor.

Originally Posted by mlkwal1

and dont over voltage the meg tool with the applied voltage .,

example: 208 motor
meg with 208 not 600 volt

What??????

Can you please enlighten us on this????

dont meg in a vac., and dont over voltage the meg tool with the applied voltage .,

example: 208 motor
meg with 208 not 600 volt

You can check any motor windings with a megger.

What makes you think he's lying?

rtac/rtaa

can you test a screw with a megger? another tech in my company claimes he checked a compressor that was throwing the breaker with a megger against a compressor that was working ok and got the same readings.???????