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Earthing in TV

Discussion in 'Electronic Basics' started by siliconmike, May 21, 2005.

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  1. siliconmike

    siliconmike Guest

    I just bought a new TV and found

    1. it had no earthing pin in its power cable (only Phase and Neutral
    were there)

    2. its audio GND (accessible from RCA connector) showed me presence of
    voltage when I touched a screw-driver-cum-mains-tester to it.

    3. I tried to touch the audio GND, but did not get a shock.


    First, why was the TV GND floating (meaning, not earthed) ?

    Can I safely connect my PC audio output to TV audio input ?

    What if I manually earthed the TV GND ?

    Thanks
    Mike
     
  2. Art

    Art Guest

    Designed with isolation between the chassis reference and any externally
    accessable connectors. Voltage you are measuring ar the avio reference is
    probably a result of static charge induced when the set in energized.
     
  3. siliconmike

    siliconmike Guest

    One thing that comes to mind is that the TV power connector might not
    have an earthing pin to protect it from lightning striking the antenna.
    Since the whole TV electronics is floating, lightning voltages (which
    are relative to earth) might prove to be less damaging.

    Any responses to my other questions below..?
     
  4. Rich Grise

    Rich Grise Guest

    Because it's chassis ground, or signal common, neither of which is Earth
    ground. (obviously, because the set is fully isolated and has no Earth
    pin).
    Probably. But why?
    Don't. It will cause ground loops, and introduce problems that you
    don't have now. This is an entire subject of study - try
    http://www.google.com/search?q=earth+ground+and+ground+loops
    You're welcome.

    Cheers!
    Rich
     
  5. Rich Grise

    Rich Grise Guest

    More likely capacitively coupled or ordinary electromagnetic induction a
    la antenna.

    Cheers!
    Rich
     
  6. w_tom

    w_tom Guest

    First some definitions and concepts. Then some simple
    experiments.

    Your are confusing earth ground with something called safety
    ground. Your TV has no safety ground connection because a
    third ground inside the TV is isolated - a floating ground. A
    voltage difference between a floating ground and safety ground
    is undefined. It may or may not harm you if you touch both
    simultaneously.

    In the meantime, anything conductive outside of that TV must
    be galvanically isolated from floating ground. Isolated does
    not mean no electrical conductivity. Isolated means minimal
    electrical connection.

    Two tests for sufficient human safety. First, plug the TV
    into a working (and pre-tested) GFCI outlet. Connect a jumper
    cable from that audio ground to the safety ground (ie a screw
    holding the wall receptacle cover plate). This test should
    not trip the GFCI. Some current will pass from that audio
    ground into wall receptacle. Current must be so low as to not
    trip GFCI.

    Second, measure that leakage current using the meter set for
    AC current. Measure well less than 150 microamps (0.15
    milliamps) from audio ground to wall receptacle 'safety
    ground'. Some leakage current should be measured. Current so
    low as to not threaten human life and not trip the GFCI.
    Galvanic isolation does not mean zero current. It means
    minimal leakage current.

    BTW, the safety ground on wall receptacle does nothing for
    lightning protection. Wall receptacle does not provide an
    earthing ground for so many reasons. The safety ground wire is
    too long (well over 10 feet), has too many splices, has too
    many sharp bends, is bundled with other non-earthing wires,
    etc. Earthing is not found at a wall receptacle for so many
    above reasons and due to excessive wire impedance. Earthing
    for lightning protection means a short wire directly to single
    point earth ground; which is different from safety ground,
    floating ground, audio ground, and motherboard ground inside a
    computer. Don't confuse these many grounds even though some
    may be interconnected.
     
  7. siliconmike

    siliconmike Guest

    Sure, I know that, but what reasons did they have in not introducing
    the Earth pin to short the signal common to the Earth..?
     
  8. siliconmike

    siliconmike Guest

    Right, thats understood. Now since the TV has 2000W exceptionally good
    audio amplifier, I would like to connect audio out from my PC to audio
    in of TV.

    As I understand, your mentioned example current (0.15 mA) would flow
    from the TV signal ground to the Sound Card GND tracks, then to the
    mother board GND tracks, then to the POWER SUPPLY gnd wire, then to the
    WALL OUTLET safety GND..
    (PC has earth pin)

    Although this current is too small, I presume it is not worth taking a
    risk. Moreover, if some static phenomenon occurs in the TV, it might
    damage the PC!
     
  9. John Miller

    John Miller Guest

    Has the brand of the TV been mentioned?
     
  10. siliconmike

    siliconmike Guest

    Samsung. (I'm in India)
     
  11. w_tom

    w_tom Guest

    If wire is grounded via computer and soundcard (a common
    mode connection), then no static problem exists. None.

    Static is not created by the TV. Voltage leakage from a
    floating ground, as described earlier, may be created by the
    TV. That leakage must be so low as to not harm humans, which
    means that leakage is too low to harm electronics. If
    worried, then make the connections before powering computer
    and TV. A redundant layer of protection.

    Earlier noted was that a defective TV (galvanic isolation
    failed) might conduct current through you when you touch both
    audio ground and safety ground simultaneously. But then this
    is what those two experiments do. They confirm the defect
    does not exist.

    I don't know if you have a GFCI (or RCD) in India to perform
    that first test.
     
  12. Ken Taylor

    Ken Taylor Guest

    Which model Samsung TV has 2000W output??

    Ken
     
  13. siliconmike

    siliconmike Guest

    CS-29T10PA

    Man this TV rocks! Now I don't need to go to theatre. I put it 10 ft
    from me and watch DVDs.. Its 29".. And cost is (in US $) $600..
     
  14. Ken Taylor

    Ken Taylor Guest

    "Peak Music Power" is a term you need to become familiar with. And while a
    29" TV is swell, it's hardly out-of-this-world. Anyway, glad you like it.
    And in answer to the original question, yes you can connect your PC audio
    output to the TV safely (assuming the PC is safe to start with). If it
    really concerns you that there may be a problem you could hunt out some
    audio isolation transformers to put between the PC and the TV, but unless
    you paid a reasonable amount of money it would degrade your audio response.

    Ken
     
  15. Ken Taylor

    Ken Taylor Guest

    Gotta spread them around further.

    Oddly enough when I used Samsung's site search engine I didn't find that
    model, but when I used Google it popped up. Hmmm, maybe they are a bit
    ashamed.....

    Ken
     
  16. siliconmike

    siliconmike Guest

    Sure I know that, but with this TV I bet one could throw a dance party.
    The sound is beautiful, and of course loud enough.

    And while a
    it.

    Its perfect for the price I guess.
     
  17. siliconmike

    siliconmike Guest


    Peter, why not do a self analysis before posting sarcastic comments for
    a nation of 1 billion ? I wouldn't be surprised if someone from India
    made you feel not very comfortable for what you just wrote.
     
  18. siliconmike

    siliconmike Guest

    Gotta spread them around further.

    Well I'm not sure who should be ashamed of surfing abilities, but here
    are the specs on Samsung's website found in less than a minute.

    http://www.samsung.com/in/products/tv/flattv/regularflattv/cs_29t10pa.asp
     
  19. siliconmike

    siliconmike Guest

    Here's what I did: Connected TV Signal earth to safety earth directly
    by a thick cable (16 SWG x 10) and then connected the PC to the TV. The
    tester stopped showing any presence of voltage on the TV signal earth,
    and the reception is ok. PC is ok.
     
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