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What is Capacitance X,Y?

Discussion in 'Electronic Basics' started by [email protected], Aug 11, 2006.

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  1. Guest

  2. Eeyore

    Eeyore Guest

    EMI suppression.

    Because if you don't use approved X and Y capacitors where required ( see IEC 60065 or 60950 for example ) you can't legally sell your
    product in most markets !

  3. Phil Allison

    Phil Allison Guest


    ** Groper alert !!

    ** Cx and Cy are CLEARLY shown on the diagrams in the spec sheet.

    ** The caps are there for EMI suppression - ie radio and TV interference.

    Caps connected across the AC supply of from AC supply to ground must be of
    special construction so they do not fail and or become a fire or
    electrocution safety hazard.

    ........ Phil
  4. Guest

    I know this is an EMI suppressor but I guess the question is not

    Since I don't know much about electronics, my question would be "what
    are Capacitance X and Capacitance Y in the EMI suppressor?" and "Why
    buyers care?" Will different Capacitance X and Capacitance Y affect a
    lot on the purchase?

  5. Phil Allison

    Phil Allison Guest

    ** DO NOT TOP POST !!!!!!!!!!!!!!!!!!

    Always post UNDER the words you wish to address.

    ** The schematic shows you that.

    ** The Y cap values are the same for each filter - this value is set by
    electrical safety LAW !

    The X cap value varies, larger value being more effective but also possible
    safety issues arise due to that high value.

    You have picked on a topic where electronic theory ( ie EMI suppression) and
    electrical safety are at logger heads - what is good for one is bad for the

    ........ Phil
  6. If you look at the "Electrical Schematics" section for the filter you will
    see a capacitor on the input, or line side, of the filter called Cx.

    The manufacturer could have just as easily called it C1 but since the value
    varies unit to unit they choose to call it Cx.

    Two additional capacitors appear on the output, or load side, of some
    filters called Cy. There are two of these thus the name 2Cy. Again, these
    could have been called C2 but since values vary from unit to unit Cy is an
    appropriate name.

    Looking at the "Additional Specifications" table you'll find that Cx is 100
    nf (nano-Farads) and Cy is 2.2 nf for the standard unit.

    Hope this answers your question

  7. Phil Allison

    Phil Allison Guest

    "Dorian McIntire"

    ** The letter X is significant.

    " Class X " capacitors are rated for use across AC lines.

    ** The letter Y is significant.

    "Class Y "capacitors are rated for use from AC lines to safety ground.

    Also, the Y cap value does not vary.

    ........ Phil
  8. Learn something new every day. I wasn't aware of the "X" and "Y" capacitor
    classification. I've actually needed some "Y" caps once to derive parasitic
    power from an 480 volt A.C. line, without using a transformer, for some
    indicators. I had a concern about capacitor failure so I designed for two
    Hi-V caps in series, on both supply lines, for twice the insulation

    I found the following document which explains "X" and "Y" caps nicely.

    Thanks Phil

  9. John Fields

    John Fields Guest

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