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Type-A RCD failing 180 degree ramp test

Former Community Member
Former Community Member
Hi


We are testing a type-A RCD (see image: "ABB") with a METREL MI 3152 (see image: "MI 3152 test").

As the image shows, the ramp test (I delta) is failing to trip the RCD for the negative half wave.


Have oneone seen this before?


Br Sebastian
attachments.zip
  • Former Community Member
    0 Former Community Member

    mapj1:

    yes that is a "ramp test" to the older hands among us.


    If you can please re-test, lying to the meter that it is an AC type, and also verify that all phase to phase voltages are similar.

    how is the meter connected - how are you choosing the phases to test - your diagram may imply live no1 and earth ,

    does it work if you shuffle them  and use say L3 and earth ?


    Is this the only RCD of its type you have tested with this meter, or has another one tested OK?


    What is the NE voltage, and where is the NE bond ?


     




    A new test has to be coordinated and will take some time to be done, unfortunately.


    The test was only done between phase 1 and earth (PE) as shown on "RCD_schema plus neutral.PNG". Also see figure 7.27 on page 105 in the METREL manual for the setup (see :"connection diagram.PNG").


    There is no NE bond on the primary side of the "T1" transformer as this is done on the supplier side (I assume (this could be a mistake))

    The NE voltage on the primary side was measured to be 0.1 Vdc and 0.5Vrms


    We have tested other RCDs of this type that have passed, but it seems to only be related to this specific installation type. 

    attachments.zip
  • 0

    seko:




    sparkiemike:




    Sparkingchip:

    Is it actually doing a ramp test?




    Don't think so, I think is the RCD tripping time because in the image the results on the instrument are in milliseconds


     




    It is failing the test that is shown as ">1500 mA" on the display. This is a "trip-out current test" (see: Metrel 3152 manual, page 108) The "trip-out test" is described as: "The instrument increases the test current in small steps through appropriate range as follows" see page: 107.


    The test stops at 1500 mA, and the test fails


     




    I’m used to seeing ramp test results displayed to one decimal point such as in the Metrel manual example as 25.5 mA for an 30 mA RCD, but stopping to think about it small increments in the test current for an 1000 mA RCD could be 10 mA or more so the test results could be displayed in substantial incremental steps increasing the chances of the trip current being displayed as 1000 mA significantly, when it could be a bit off that.


    I wonder how many increments there are between 1000 mA and 1500 mA when it fails the test, could it be going up in 100 mA steps or more?


    If there’s another tester to hand it could be worth doing another RCD ramp test to try and pin down what the actual trip currents are a bit more precisely.


    Andy 

  • Former Community Member
    0 Former Community Member

    Sparkingchip:




    seko:




    sparkiemike:




    Sparkingchip:

    Is it actually doing a ramp test?




    Don't think so, I think is the RCD tripping time because in the image the results on the instrument are in milliseconds


     




    It is failing the test that is shown as ">1500 mA" on the display. This is a "trip-out current test" (see: Metrel 3152 manual, page 108) The "trip-out test" is described as: "The instrument increases the test current in small steps through appropriate range as follows" see page: 107.


    The test stops at 1500 mA, and the test fails


     




    I’m used to seeing ramp test results displayed to one decimal point such as in the Metrel manual example as 25.5 mA for an 30 mA RCD, but stopping to think about it small increments in the test current for an 1000 mA RCD could be 10 mA or more so the test results could be displayed in substantial incremental steps increasing the chances of the trip current being displayed as 1000 mA significantly, when it could be a bit off that.


    I wonder how many increments there are between 1000 mA and 1500 mA when it fails the test, could it be going up in 100 mA steps or more?


    If there’s another tester to hand it could be worth doing another RCD ramp test to try and pin down what the actual trip currents are a bit more precisely.


    Andy 


     




    The increments are 50 mA

  • Former Community Member
    0 Former Community Member

    seko:



    We have tested other RCDs of this type that have passed, but it seems to only be related to this specific installation type. 



     




    Hi seko, could you clarify if you mean it is related to this specific installation, or it has happened before on this type of installation?


    Is it a new installation verification or an EICR or another purpose?

  • Former Community Member
    0 Former Community Member

    WB³:




    seko:



    We have tested other RCDs of this type that have passed, but it seems to only be related to this specific installation type. 



     




    Hi seko, could you clarify if you mean it is related to this specific installation, or it has happened before on this type of installation?


    Is it a new installation verification or an EICR or another purpose?


     




    It has happened before "on this type of installation". It is a new installation. 

  • 0
    This 1000 mA RCD is it still rated at 6 mA DC or less the same as an 30 mA Type A RCD?


    Andy
  • Former Community Member
    0 Former Community Member

    seko:




    WB³:




    seko:



    We have tested other RCDs of this type that have passed, but it seems to only be related to this specific installation type. 



     




    Hi seko, could you clarify if you mean it is related to this specific installation, or it has happened before on this type of installation?


    Is it a new installation verification or an EICR or another purpose?


     




    It has happened before "on this type of installation". It is a new installation. 


     




    Thanks for the reply, my suggestion although I haven't ever ramp tested an RCD would be to try repeating the tests in manual mode rather than automatic, it might be that the RCD gubbins gets a bit too warm after closely repeated operations?

  • Former Community Member
    0 Former Community Member
    Hi


    Here are some updates:


    The RCD has been tested outside the installation (see: "test setup") A current sense resistor of 1 ohm is inserted in series with the green earth cable (not visible on the image).


    The scope recording can be seen in "Full recording". The failing ramp test (negative) is marked with "6" and zoomed versions are "6-1" and 6-1-1"

    METREL has verified that the tester makes a pre-test as seen in "6"


    To me the waveform shape looks good (despite some small spikes) and the RMS values are also reaching 1.5 A before the test stops and fails because the RCD didn't trip. So it must be a faulty RCD or are these minor spikes the reason?

    attachments.zip
  • 0
    looks faulty to me.  Very Surprising though.
  • 0
    I cannot say I have ever tested a RCD to that extent.


    Andy

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