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Should I HIPOT before or after other tests?

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    #1
  1. Join Date
    Mar 2016
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    Should I HIPOT before or after other tests?

    My electrical knowledge is limited, but I'm responsible for reviewing some testing practices for our company and trying to standardize them. We have a few product lines that we conduct our functional testing cycle followed by a HiPOT test, and a few other product lines where we HiPOT test it first and then do our functional testing.

    I'm trying to understand if there is a standard practice of running the insulation testing after or before other tests due to the possibility of one set of tests affecting the other set of tests. These are all AC units and we are conducting an AC HiPOT test.

    Any help in understanding what the best practices would be is appreciated.

    Cheers.

    ----------------------------------
    It has now been about 3 months I don't seem to be getting the type of advice that I am looking for, so let me start again.

    I have units that in the field will have operating conditions of:
    Either 120V or 240V AC
    less than 2A draw
    Think of it as a speed controlled window fan for all intensive purposes.

    Some of the common components used are:
    120V or 240V C frame 1.2A motors
    SPT-2 and SPT-3 wire (aka "lampcord")
    UL3173 XLPE 18g wire
    Various 18g insulated connectors
    Various mechanical switches
    Various rheostats

    I have two options for testing to try to standardize and do not understand the implications of running each test sequence.

    Option A:
    Apply either 120V or 240V power as appropriate to check all switch routings and "run" functionality (5 to 30 second run time).
    Apply an AC HiPOT test to confirm insulation does not "leak".
    Concern: In this scenerio it appears that the HiPOT test could (in very rare cases) burn out the unit and by not running the functional test first could cause a dead unit to get to our customers.

    Option B:
    Apply an AC HiPOT test to confirm insulation does not "leak".
    Apply either 120V or 240V power as appropriate to check all switch routings and "run" functionality (5 to 30 second run time).
    Concern: In this scenerio it appears that the application of power could cause a situation where the HiPOT test would fail if rerun. My opinion of this is primarially due to the run time of the motor and the switching process.

    I am trying to understand:
    Which (A or B) has the least risk of a failure getting past the testing.
    If there is a "standard" method for order of test application based on the stresses / failures that could be missed after each test.

    Cheers.
    Last edited by DJ-Jokes; June 30, 2016 at 07:14 AM.

  2. #2
  3. Join Date
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    Generally speaking its better to do the DC insulation test first (insulation resistance) because its done at a much lower voltage. Any insulation problems would show up in this test. Do the AC withstand test only if insulation resistance values are acceptable.

  4. #3
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    Quote Originally Posted by madMAX View Post
    Generally speaking its better to do the DC insulation test first (insulation resistance) because its done at a much lower voltage. Any insulation problems would show up in this test. Do the AC withstand test only if insulation resistance values are acceptable.
    Thanks madMAX. I'm not familiar with that type of test as it is not something we currently do. To be a bit more explicit, we are making wiring harnesses that can contain some of switching devices attached to a small C frame motor. The HiPOT test is conducted because of customer / industry requirements. I realize that the HiPOT test does by its nature cause the insulation to be stressed and that repeated testing is not desired.

    That is part of the reason for my question. It seems to me that conducting the HiPOT prior to any functional testing may cause an unexpected safety issue, but running it after the functional test may cause the unit to be DOA.

    So is your recommendation that we insert an insulation resistance test first, followed by a HiPOT and then end with a functional test?

  6. #4
  7. Join Date
    Jun 2016
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    It depends what you are testing. Are you testing MV or HV solid dielectric cable by chance?

  8. #5
  9. Join Date
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    No, consider it to be similar to an oscillating floor fan or a lamp or whatever. It is just a consumer electrical product running at either 120 or 240V. I've revised the original thread description to give more details of the components involved.

  10. #6
  11. Join Date
    Dec 2014
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    Given the new details, a simple 1000V megger test would be sufficient. The insulation of that wire is most likely rated 600V (look at the markings on the wire) a hipot would compromise the insulation. Measure each wire to ground and each wire to each other for 1 minute. You are looking for 100 Megohms but its not unheard of to turn something on with 1 Megohm. You might find this article helpful: http://testguy.net/content/195-Basic...istance-Tester

  12. #7
  13. Join Date
    Jan 2017
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    Qustion is already answered but i agree, normally do meggering first to ensure cable stability

  14. #8
  15. Join Date
    Sep 2017
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    I would not hipot anything rated 240v. A 1000v megger is sufficient. What voltage are you using to hipot test?

  16. #9
  17. Join Date
    Sep 2019
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    Quote Originally Posted by DJ-Jokes View Post
    My electrical knowledge is limited, but I'm responsible for reviewing some testing practices for our company and trying to standardize them. We have a few product lines that we conduct our functional testing cycle followed by a HiPOT test, and a few other product lines where we HiPOT test it first and then do our functional testing.

    I'm trying to understand if there is a standard practice of running the insulation testing after or before other tests due to the possibility of one set of tests affecting the other set of tests. These are all AC units and we are conducting an AC HiPOT test.

    Any help in understanding what the best practices would be is appreciated.

    Cheers.



    ----------------------------------
    It has now been about 3 months I don't seem to be getting the type of advice that I am looking for, so let me start again.

    I have units that in the field will have operating conditions of:
    Either 120V or 240V AC
    less than 2A draw
    Think of it as a speed controlled window fan for all intensive purposes.

    Some of the common components used are:
    120V or 240V C frame 1.2A motors
    SPT-2 and SPT-3 wire (aka "lampcord")
    UL3173 XLPE 18g wire
    Various 18g insulated connectors
    Various mechanical switches
    Various rheostats

    I have two options for testing to try to standardize and do not understand the implications of running each test sequence.

    Option A:
    Apply either 120V or 240V power as appropriate to check all switch routings and "run" functionality (5 to 30 second run time).
    Apply an AC HiPOT test to confirm insulation does not "leak".
    Concern: In this scenerio it appears that the HiPOT test could (in very rare cases) burn out the unit and by not running the functional test first could cause a dead unit to get to our customers.

    Option B:
    Apply an AC HiPOT test to confirm insulation does not "leak".
    Apply either 120V or 240V power as appropriate to check all switch routings and "run" functionality (5 to 30 second run time).
    Concern: In this scenerio it appears that the application of power could cause a situation where the HiPOT test would fail if rerun. My opinion of this is primarially due to the run time of the motor and the switching process.

    I am trying to understand:
    Which (A or B) has the least risk of a failure getting past the testing.
    If there is a "standard" method for order of test application based on the stresses / failures that could be missed after each test.

    Cheers.

    With something like this you need to check the cable rating. You would only Megger something this low voltage. If considered control wiring I would Megger at 500v, if greater then you can Megger at 1000v. HiPot will almost definitely damage the wire.

  18. #10
  19. Join Date
    Jul 2016
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    It would be interesting to know what you consider as a hipot test. Because given the information, as stated above you should only test with a dc megger to the values pointed out in table 100.1 of NETA , depending on the rating of this wiring.

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