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  1. #14
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    Quote Originally Posted by Hrdworkingacguy View Post
    M500 is junk. When customers say they megged a compressor and want a warranty replacement because it read "bad" I don't accept it as a valid test. I offer to go out and use my fluke. It's about 70% aren't actually bad.
    You shouldnt need to go that far.

    The test is, if it starts and runs.

    Ive seen quite a few compressor meg very poorly that still will start and run.




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  2. #15
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    Quote Originally Posted by pageyjim View Post
    The M500 is a low end megohmmeter that can be had for app $80-90 probably. I don't know what you paid for it at Johnstone. I had a Megger 420 which puts Fluke megs to shame imho and the M500 gave comparable spot readings, the Megger does a bit more. I found the M500 to be very useful especially when talking to a homeowner.
    Megohmmeters are probably the most misused and least understood tool in an HVAC tech's toolbox. Many will say that a residential tech does not even need one. They are used more as a predictive tool for future failure more than anything and best used if a log is kept. They are not really needed to tell if a compressor or motor has failed already. If you get a caution or "bad" reading it is a good idea to do a moisture test on the system bc that can give you a false reading.
    This site has fantastic information and many threads on megohmmeters but they are lacking imo and there is a lot of bad info mixed in with the good.

    Good luck
    Thanks Again!

    Im Working For A Insurance Company And They Requires Me To Meg Out The Blower, Inducer, And Compressors When I Go Out And DonA Claim And I Want To Make Sure I Have The Right Tool For The Job.

  3. #16
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    M500 Megohmmeter By Supco

    Quote Originally Posted by cook42 View Post
    Thanks Again!

    Im Working For A Insurance Company And They Requires Me To Meg Out The Blower, Inducer, And Compressors When I Go Out And DonA Claim And I Want To Make Sure I Have The Right Tool For The Job.
    The m500 only has the capability to meg at 1 voltage -500v

    Generally speaking, you want to meg at a voltage comparable to the normal operating voltage of the motor, or wiring system.

    A compressor will tolerate 500 v, but Im not too sure about the 120v draft and blower motors.

    Thats where something like a Fluke 1507 would come in handy - but its about 5 times the cost.

    There are other less expensive meters that have that low of a voltage output that is selectable, but I cant speak to the quality of those.




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  4. #17
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    It is generally advised to meg motors out at up to twice the rated voltage. I would personally not be too concerned with doing tests at 500vdc. Many will say if a problem shows it was likely there to begin with. But it is of course best to use up to twice the rated voltage only. I would caution you from megohming ECM motors in general or at least know if it is advised on those particular motors you are working on.
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  5. #18
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    You can find a good read about insulation testing here (links at the bottom). A stitch in time. Has more info than most probably want to know but worth reading.

    Admittedly, many aspects of using a megger in practical everyday ways still escapes me. The little bit of reading I have done (Im open to having my mind changed) they dont seem as useful for single use, spot testing as some make them out to be. Theres many variables that can affect your readings and most importantly if being done as a single spot check, you have no reference for comparison.

    They seem to really shine if being used a part of a routine maintenance program to log the results. Obviously the log will show you any trends in change. To that point, sadly most commercial PM contracts do not build in time to properly Meg motors or conductors to create the necessary log history to make them useful. I really dont see the value in one for residential work.

    That home warranty companies policy of you doing this sounds a bit sketchy to me. Not on your end but theirs. You should ask them for their desired/minimum Megohm values for this testing procedure. Its unlikely they have a clue but rather just know guys condemn more parts using this misunderstood test equaling more money changing hands. Just my thoughts anyway.

    http://www.biddlemegger.com/biddle/Stitch-new.pdf
    Regards,
    Ron

  6. #19
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    The spot check is really only useful for when your 1.5VDC meter can’t find the short. If you have enough experience, the spot check can work but it takes many years and thousands of readings to develop.
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  7. #20
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    Quote Originally Posted by jayguy View Post
    The spot check is really only useful for when your 1.5VDC meter cant find the short. If you have enough experience, the spot check can work but it takes many years and thousands of readings to develop.
    This is a interesting thought. While Im curious as to how a spot check really tells one much of value without a reference (such as a trend log), I think its fair to say the bigger problem is in the latter part of the statement. While most will put in many years, few will even do dozens of Megaohm tests, let alone thousands. We may agree that a solid multimeter is going to be adequate to tackle most everyday service issues in the field. I can admit to being a part of this crowd, I think solid understanding of practical and useful purposes of a Megger still eludes most of us for daily purposes if were being honest. With factors such as refrigerant, moisture, temperature, etc. theres just so many variables at play in understanding all the factors which can affect such a test. Its certainly a interesting subject.
    Regards,
    Ron

  8. #21
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    I apologize. I meant “spot test” for my first sentence. I meant “one test” for the other place I said “spot test”. If you have never seen this particular piece of equipment before, certain checks like the “dielectric test” or (better yet) the “polarization test” can tell you a lot from a single test...not as much as a trend, but quite a bit of information none the less.
    Don't step on my favorite part of the Constitution just to point out your favorite part.

    Political Correctness is forced on you because you have forgotten decency.

    Technically speaking, they are all heat pumps.

  9. #22
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    Quote Originally Posted by heatingman View Post
    You shouldn’t need to go that far.

    The test is, if it starts and runs.

    Ive seen quite a few compressor meg very poorly that still will start and run.




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    I was talking about Mitsubishi M & P or city multi systems where there is usually a board or two that could be bad or the compressor could have failed and taken things out.

    Bad meg ohm readings could come from bad oil, moisture, acid, windings that are startling to fail. It's more then just good or bad...
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  10. #23
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    Quote Originally Posted by Hrdworkingacguy View Post
    I was talking about Mitsubishi M & P or city multi systems where there is usually a board or two that could be bad or the compressor could have failed and taken things out.

    Bad meg ohm readings could come from bad oil, moisture, acid, windings that are startling to fail. It's more then just good or bad...
    My point was - does not matter what brand of meter. Cheap junk, or a top dollar Megger or Fluke, you can have a very low meg ohm reading - from any of the reasons you listed, and even a strait up winding breakdown, and the motor can and will still run, but test poorly.

    So - I guess my real point is - a Low Meg reading should not condemn a compressor.

    But - I think were on the same page.


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