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being shocked by Amp casing

Discussion in 'Electronic Basics' started by RobZ, Jul 9, 2008.

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  1. RobZ

    RobZ Guest

    hi all, perhaps slightly off-topic but you guys have been of great
    help to me in the past

    When I was installing a new hifi amplifier last night, I realised i
    was being lightly shocked each time i touched the amplifier case while
    I was lying on the floor trying to re-route some of the speaker cables
    behind the cabinet.

    The shock is definatly between the Amplifier case and the floor. ( no
    frayed wires - new installation)

    the amplifier is supplied by a 2 wire AC cord ( no earth )

    what is causing this?

    is this dangerous?

    Can I add my own earth wire ( joined to the case, to the AC socket
    Earth Plug) ? will this help?
  2. Eeyore

    Eeyore Guest

    A switched-mode power supply almost without doubt. I imagine the amp is
    compact and lighweight for its power rating.

    As long as it's been designed to IEC standards, no. It's called 'leakage
    current' and has allowable limits that will cause you no harm.

    If the amp has a dedicated ground terminal do feel free to add a
    *sepearate* 'earth wire' tot his. Otherwise don't tinker with the mains
    witing AT ALL.

  3. Eeyore

    Eeyore Guest

    I very much doubt it ! Inter-ground potentials should *never* be detectable
    by touch. If they are, get an electrician QUICK !

  4. Eeyore

    Eeyore Guest

    Your answer is mostly corrrect in that you mention the effect of the suppresion
    filter which by default must create a leakage current potential. There is
    however, internally in the PSU typically another 'Y cap' that adds to the fun.

  5. Eeyore

    Eeyore Guest


    I have seen tiny sparks in low light, interconnecting pieces of IT equipment.

  6. What devices did you have connected to the amplifier? Were they properly
  7. Jasen Betts

    Jasen Betts Guest

    capacitance from live to the body of the amplifier,
    if the power cord has a reversible plug on either end try reversing it.
    if this is new equipment probably not.
    almost certainly, especially if the maker has provided an earthing
    terminal on the amplifier, but if you have other audio equipment that is
    already earthed it may be better to earth your amp to that equipment.

  8. Eeyore

    Eeyore Guest

    Totally unrelated to this problem which is I will guarantee 99.99% certain to be
    the use of filter caps in SMPSs that cause small leakage currents.

  9. neon


    Oct 21, 2006
    the chassis is not tied to earth ground so do tie a wire not to the socket but to a water pipe or whatever that gets to earth eventualy. this amp is probably made in china life is cheap there.and is not UL approved.
  10. Eeyore

    Eeyore Guest

    FWIW you have my sympathies.

    IEC 60065 allowable leakage current off the top of my head is 2.4mA or so.
    What's more the MAIN culprit isn't even usually in the common mode filter but a
    little known part that crosses the pri-sec isolation (a Y cap) to reduce EMC
    compatability problems.

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