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Thread: Is a megger an obsolete instrument?

  1. #41
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    Quote Originally Posted by Core_d View Post
    Are you trending insulation resistance on these systems?


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    We record the information yearly on our annual inspections. Not sure if that truly qualifies at trending, but we do have data to look at if something starts to change. In a chiller, moisture will start to show itself in other ways before the motor, traditionally. Chiller motors go to ground for a variety of reasons. Usually it's something like too many starts and stops, loose connections, a bad contactor, etc. Most of the large machines don't start and stop a lot. That's when the wear and tear on the windings occurs.

    Unlike normal industrial motors, we have temp sensors on our motors and tightly control amperage loading through the controllers. If a motor starts to operate out of parameter, the chiller spits out an alarm.

    We do have some very very large pump motors that we meg with the maintenance guys once a year and they watch that data.

    Not really an answer, but it's all I got.

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  3. #42
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    Is a megger an obsolete instrument?

    Quote Originally Posted by BennyD View Post
    I'm not medium voltage certified but do have to get into starters and at motors from time to time. We have local electricians lock it out and ground the leads. We then walk the lockout and make the electrician touch it with his bare hand. If he won't, we won't.
    I know the spec as well and agree that 99% of the time, a 1kV megger is enough (and not to post it here). I got questioned about it once about a 4160V chiller that kept tripping the ground fault. I said motor was fine. They didn't believe me. Come to find out, whoever set up the trip points in the switch gear, had set it up wrong and was off by a factor of 10...
    Do you resistance trend these motors as part of a PM?


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  4. #43
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    Quote Originally Posted by JCN View Post
    I use a UEI IRT3 analog for my daily needs. We do have access to a Fluke 1550(?) that will go to 5K. Yes, I am medium voltage certified.

    There are meggers available in the 10k output range, but they aren't usually needed. If you have a 4,160 motor that you suspect of going to ground, you will see it with a meter set to 1K pretty quickly. Those motors are only pulling 50-75 amps at full load on a 1,000 hp+ motor. 13 kV chillers aren't uncommon, but less common in our area than 4,160's.

    The 19XR's are more common in 480 V than they are in the more exotic medium voltage configuration. The CVHF that I posted about earlier is a 480 machine.

    I could post our specs, but that isn't appropriate for an open forum. I thought we were just discussing whether it was obsolete or not. ???
    Yes, but I just wanted to distinguish between megger types and usages. Most of the megger questions posted here are in reference to toy meggers, which I feel are next to useless and have led to many improperly condemned compressors, especially true for the Supco M500.

    When a megger is required, such as in your case, that generally won't be discovered by reading replies here. The literature will specify it, or you will have been instructed in its use during some type of training.

  5. #44
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    Quote Originally Posted by Core_d View Post
    Do you resistance trend these motors as part of a PM?


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    I'm on par with JCN there. It is taken at every startup and usually on an APM. We don't "trend" but the info is there if needed. We have a good mix of 480V and 4160V chillers. Nothing above 4160V in our area that we take care of. No medium voltage drives either...
    I can't say I've ever found a bad motor by megging alone. It's usually blowed up good by the time I get there. I have found a lower than normal (but still pass by spec) on a new or reman compressor. Once evacuated and dried out, I check after breaking the vacuum with refrigerant and it usually gets much better.
    -----Stop, step back, relax and have another go at it.-----

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  7. #45
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    Quote Originally Posted by BennyD View Post
    I'm on par with JCN there. It is taken at every startup and usually on an APM. We don't "trend" but the info is there if needed. We have a good mix of 480V and 4160V chillers. Nothing above 4160V in our area that we take care of. No medium voltage drives either...
    I can't say I've ever found a bad motor by megging alone. It's usually blowed up good by the time I get there. I have found a lower than normal (but still pass by spec) on a new or reman compressor. Once evacuated and dried out, I check after breaking the vacuum with refrigerant and it usually gets much better.
    I concur. No medium voltage drives here either. I have had megger readings cause me to question a screw compressor and dig deeper before condemning it. The meg reading is never enough by itself to declare one dead. These are REALLY expensive machines/parts and there is a procedure for declaring something dead.

  8. #46
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    Anything above 480v in america is medium voltage no?


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  9. #47
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    Quote Originally Posted by Core_d View Post
    Anything above 480v in america is medium voltage no?


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    I can never remember where 600V falls in that scale. Is 600 in medium voltage or the last step of low voltage? It doesn't really matter, it will bite the hell out of you either way.

  10. #48
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    Quote Originally Posted by JCN View Post
    I can never remember where 600V falls in that scale. Is 600 in medium voltage or the last step of low voltage? It doesn't really matter, it will bite the hell out of you either way.
    I know we are not supposed to work on anything over 600V without an electrician. Pretty sure 600V is the last step before medium voltage.
    -----Stop, step back, relax and have another go at it.-----

  11. #49
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    Quote Originally Posted by BennyD View Post
    I know we are not supposed to work on anything over 600V without an electrician. Pretty sure 600V is the last step before medium voltage.
    That's right. It's on that stupid site assessment thing we're supposed to do before every job.

  12. #50
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    Are you both canadian?


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  13. #51
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    Quote Originally Posted by JCN View Post
    That's right. It's on that stupid site assessment thing we're supposed to do before every job.
    Not quite there yet... Soon
    -----Stop, step back, relax and have another go at it.-----

  14. #52
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    Quote Originally Posted by Core_d View Post
    Are you both canadian?


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    No, just work for the same company in different parts of the country.

  15. #53
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    Quote Originally Posted by JCN View Post
    No, just work for the same company in different parts of the country.
    From what i understand 480v is the highest utility in the states in canidah its 590 or something. Thats why i ask.


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  16. #54
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    Quote Originally Posted by Core_d View Post
    From what i understand 480v is the highest utility in the states in canidah its 590 or something. Thats why i ask.


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    I do have an odd site that has (4) 600V 1200 ton CVHB's.
    -----Stop, step back, relax and have another go at it.-----

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  18. #55
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    Quote Originally Posted by Core_d View Post
    From what i understand 480v is the highest utility in the states in canidah its 590 or something. Thats why i ask.


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    There is 600V in some parts of the US. We have one site that has 575 on it. We usually see medium stuff at large sites and in industrial settings.

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  20. #56
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    Why doesn't my like button work anymore?

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  22. #57
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    Quote Originally Posted by JCN View Post
    Why doesn't my like button work anymore?
    Not sure, i use tapatalk mine has worked, not the first ive heard of it. Thanks for clarification on the subject.


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  23. #58
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    Quote Originally Posted by JCN View Post
    Why doesn't my like button work anymore?
    IT knows. It's broken on all platforms except the Tapatalk app.

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  25. #59
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    Quote Originally Posted by HVAC_Marc View Post
    IT knows. It's broken on all platforms except the Tapatalk app.
    Thanks Marc.

  26. #60
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    600 is low voltage, 601 is medium voltage.

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