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Possible grounding issue - HDMI over CAT-6 electrical arc

  1. May 12, 2015 #1


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    I was recently asked to help with some A/V stuff at my church. The goal was simple: Display HDMI video from a laptop to two LCD TVs. Since distance was an issue, I purchased an active HDMI-to-Ethernet converter.

    I've included a diagram for reference.

    When I went to plug the 3' HDMI cable from the splitter to the first LCD TV, a huge electrical arc occurred when I barely touched the HDMI cable to the back metal plate of the TV. This fried the LCD TV and the HDMI-to-Ethernet converter.

    I suspect grounding issues, but I don't know enough about HDMI to know if that could be the problem. How would I determine if grounding is a culprit here?

    Attached Files:

  2. jcsd
  3. May 12, 2015 #2
    I would measure the voltage between the two things that arced, the outside of the hdmi cable and the tv. Seems like you have 120 volts or more between them where there should be little or none?

    edit, do this first. Also get a simple electrical tester and check the outlets in question for an open neutral.
  4. May 13, 2015 #3

    jim hardy

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    Something is indeed VERY wrong.

    Need to locate trouble , is it in the equipment or in the house wiring?

    What else was plugged into the TV that fried ?

    Do the TV and your new "adapter" have power plugs with two , or with three prongs ?

    Your drawing shows two TV's already connected by a fifty foot HDMI cable...
    was that cable plugged in at both ends before you tried to connect the splitter?

    You need to get a continuity checker.
    I like the $10 tester from Walmart


    and check from the TV's metal part where you touched the cable to both flat prongs on the TV's power cord.
    First you touch the two meter leads together and verify the needle swings all the way to right, where the top scale says 0 Ω. Adjust the little wheel on left side of meter for indication of 0 Ω
    then touch meter leads to the power cord prongs and metal of the TV.
    There should be no movement of the needle on any of the three OHM scales, RX10, RX100 or RX1k .
    Do that at both the near and the far TV.
    If your TV has a third ground prong that's round and a little longer, check there too. Continuity there is okay

    Then same check at both those powered HDMI gizmos.
    There you'll measure from the metal part of HDMI cable to the flat prongs of the wall adapters that came with the units.
    Needle movement there says big trouble.
    If they have a third prong for ground, which i doubt, continuity there would be okay.

    of course get one of these and check all outlets involved.
    about eight bucks (was four last year but there's no inflation)

    good luck

    old jim
    Last edited: May 13, 2015
  5. May 16, 2015 #4
    Jim, I'm not actually surprised you'd go for the cheap analog meter. And I mean that with utmost respect!

    Something to remember with the plug tester (GB changed the style? have not bought that flavor in a while I guess)...

    Although it doesn't say so on the output matrix, if the tester lights all three lights (orange orange red) then you definitely have an open neutral to the source, and two lines are talking to each other, potentially frying things and could very easily be pushing potential to ground down a normally "grounded" part. When two ungrounded lines of a system can't see the common ground they are expecting but can still see each other, well, VERY wierd things can start happening. Unplug everything and call an electrician or some other qualified person to check the line voltage circuits.

    Computers and such can operate for a surprising time period on overvoltage caused by an open neutral but eventually something will leak too much magic smoke.

    Of course this assumes a 120v grounded system of some sort, if this is eurozone stuff you are on your own for what I can offer!
  6. May 16, 2015 #5

    jim hardy

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    Thanks, Krater.

    The more complex the instrument the more ways it can fool you.

    That's true of people, too. " the meter doth protest too much, methinks. "
    Give me an Ophelia any day.
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