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There is a reason why there are megger tests....and then they are hi-pot tests.

A megger test is supposed to be non-destructive. Every insulation class has a rating. We are supposed to be protecting investments, not harming them.

Originally Posted by JayGuy

no damage is going to occur unless it was already there to begin with.

Like Tom Petty says "you can believe what you want to believe..."

Originally Posted by KnewYork

Yeah, until you find one that the insulation is compromised...

that's the goal. at 2mA DC of maximum current, lightning bugs have more power in their butts than a megger. no damage is going to occur unless it was already there to begin with.

Originally Posted by JayGuy

1000 volt is usually more than enough...i test ALL motors at 1000 VDC. yes, even 115VAC motors and they do just fine.

Yeah, until you find one that the insulation is compromised. Industry standard for DC test voltages of 120-
240 VAC motors is 500 VDC. Certainly you can continue juicing those little motors to 1000 VDC until your luck runs out.

The manufacturers of 4160 V motors prefer a continuous application (10 minutes) of approximately 2500 VDC rather than shorter durations of 5000 VDC.

Originally Posted by Lightning_Boy

I currently don't work on anything bigger than 460/480v.
Is it worth getting a 5000v capable meg ohmmeter ?
Really liking the AEMC stuff. 1050 model has my attention but not my budget :0(

That's a really nice meter. It would be overkill for most of us though. I have the AEMC 1026.

1000 volt is usually more than enough...i test ALL motors at 1000 VDC. yes, even 115VAC motors and they do just fine.

I currently don't work on anything bigger than 460/480v.
Is it worth getting a 5000v capable meg ohmmeter ?
Really liking the AEMC stuff. 1050 model has my attention but not my budget :0(

Originally Posted by LU91Tech

Any rule of thumb on which voltage to do a test. Our megger at work has selectable voltages of 500,1000,2500,and 5000 to test with.

Typically around twice the supply voltage. For a 230 volt motor use the 500 volt setting, etc.

Any rule of thumb on which voltage to do a test. Our megger at work has selectable voltages of 500,1000,2500,and 5000 to test with.

I am required to do a Meg/Ohm test of the compressors on my annual inspections. Customer requirement. 2 Ton to 20 Ton. I usually do it at the contactor???

I love my old hand crank Biddle. If buying new today I'd go AEMC.

Match the megger to the voltage classes you work with. If you work on 4,160 motors you need a 5,000 VDC unit.

IMHO top uses for a megger are establishing trends and looking for problems that aren't obvious. Can be a time saver on shorts that come and go or are moisture related. It does require that one have an idea of what a pass/fail reading is. I would not call 100,000 ohms to ground "okay". What is okay on a 120 VAC motor isn't the same as what is okay on a 4160 motor.

Also need to know when not to use one, such as a hermatic in a vacuum.

Checked grainger link. No longer in catalogue.
Thinking of spending $600-$800 on a good one.
Is it worth going upto a 5000vdc capable unit or not?? Will the readings be more accurate?

Thinking Mitchell, Megger or aemc at the moment...

if the motors are 460v they have a higher rate of going nuke then 208V ones.might want to take a megger reading on a new one just to see if the others change over a season or on spring start up after a blizzard or two melts into the windings and those top bearings..

I wasn't looking for bad bearings, that was just something that I did notice about the motor.As far as being conclusive the unit is working fine ,that's good enough for me.There are times when you're good and other times when you're lucky.I bought my megger at a pawn shop for around $40.00,but in this case I wouldn't take a gold quarter for it.When I started out I debated whether or not to get one but I couldn't pass this up.There haven't been many times that I have had to resort to this but I don't like to borrow things and it got the job done.Hope you have a great week!

Originally Posted by aikenite

On a carrier 50tc there are 4 condenser fans.They are fed by 15 amp fuses The fuses had blown several times and other guys would just replace the fuses and it would work for a day or two.I decided to find and correct the problem so I isolated each motor and megged the motors.1 motor gave odd readings compared to the other 3.We ordered a new motor and replaced it The unit has been working fine for a couple months.Like i said ,I don't do many start-ups so when I break out my megger I am looking for something unusual.By the way, the motor that was bad had a lot of oil inside as if the bearings were bad.

Repeated over amping and overheating of the windings could break down the insulation enough to show a difference in leakage current between that and the other identical motors. I wouldn't have thought of testing for bad bearings like that, but in hindsight the idea seems to have some merit despite its lack of conclusiveness. Thanks for sharing that.

On a carrier 50tc there are 4 condenser fans.They are fed by 15 amp fuses The fuses had blown several times and other guys would just replace the fuses and it would work for a day or two.I decided to find and correct the problem so I isolated each motor and megged the motors.1 motor gave odd readings compared to the other 3.We ordered a new motor and replaced it The unit has been working fine for a couple months.Like i said ,I don't do many start-ups so when I break out my megger I am looking for something unusual.By the way, the motor that was bad had a lot of oil inside as if the bearings were bad.

Originally Posted by aikenite

I recently used mine to find a bad condenser motor that read o k with a meter.I will admit that i don't use it often,but in this case it saved the day!

Care to elaborate? Was it tripping the breaker?

I recently used mine to find a bad condenser motor that read o k with a meter.I will admit that i don't use it often,but in this case it saved the day!

We have an oldish Biddle Megohmmeter, runs on 110v and produces up to 5,000vdc. Used it today on a big centrifugal motor, comes in handy when you want to know the condition of the insulation. It may even help make you look like you know what your doing.

...Ron

I use mine any time the need arises, such as annuals, motor issues, checking out wire runs in conduit and the presence of moisture to any of the above. On annuals it goes along with an oil sample and vibration analysis. This way you can trend a system, compressor or motor.-GEO