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General thread on basic electricity and safety for connected AV appliance

  1. #1
    Gold Member nevinjohn's Avatar
    Join Date
    Nov 2010

    Default General thread on basic electricity and safety for connected AV appliance

    Hello everyone,

    We have been discussing all the issues from the operator point of view! Some of us might have noticed the small shock when touching the rear panel, or even when we touch the appliance itself... yes, dont simply blame it on earthing. Thats what everybody says, but check this senario.

    I recently purchased a LG LED LCD TV, 22''. It has got a power adaptor, like what a laptop has. Basically, it works on dc. From day one, I noticed a slight shock when ever I touched the rear connection panels (AV, component..etc). I reported this to LG, for which they asked me check the earthing. Well, first thing I need to know is,..
    1. Since an adaptor is used, and the output terminal consists of two terminals only, positive and earth, how is it connected with the TV?

    2. Same is the case with laptop adaptors, all it needs is dc supply then what is the need of the third big pin/earthing?. Afterall the laptop is not connected to the ground. So what is the internal connection like?

    Then I did something which amazed me, I took a tester, and touched the end of the terminal, which is plugged into the laptop, and it lighted up!! Same was the case with the TV's adaptor. But note that the current was not of lethal amount. When I touched, I didnt feel any shovk, but a small tinking sensation!!

    Now I was very sure there was no issue with the adaptors, but there was something wrong with the house wiring. Next, I removed the earth pin, and tried, ans still the tester lighted up!! What could be wrong?

    I moved out to a new apartment and noticed that everything is working fine here. I dont get that small shock on touching the appliance, also the tester doesnt light up when touching the dc feed end. I removed the earth pin and repeated the above steps, and here also it was fine, no shock, no light on tester!!!

    So the issue was indeed related to wiring in my previous apartment. Has anyone got any clues? Electrical Engineers????!!!

  2. #2
    Admin's Avatar
    Join Date
    Jan 2006


    I once had a problem with a UPS as my computer used to restart when the power supply switched from mains to the invertor and after much arguing the luminous guy came to my place to see whats wrong and found that the electric socket wiring was not done right... the positive wire was going into the one where negetive was suppsed to be so I got the whole house's wiring checked by an electrician who then confirmed that the rest of the wiring was fine it was just that particular socket that had incorrect wiring.. most applianced do not get afected with this fault but some stuff does and an online UPS is one of them.. I wonder if there is such a fault in the wiring at your house??

    I am not an electirician and this is just my guess Would be interesting to hear from some one who knows this stuff well..

  3. #3
    Gold Member nevinjohn's Avatar
    Join Date
    Nov 2010

    Thumbs up

    Yes, this is a common mistake electricians make while wiring.
    And, ofcourse this affects sensive electronics, and an online UPS is a good example.

    Once while installing a split air conditoner at my home, as a trial connection, the terminals were connected in reverse. I noticed that I get a small shock when touching the outdoor unit. The technicial (a Bluestar guy) immediatly told me that the electrician had reversed the connection. Anyway, after the terminals were connected propoerly, there were no more leaks!!

  4. #4
    Join Date
    Aug 2007


    Some power supply boards in the market have
    LED indicators to show wrong connections.
    Ground open / polarity reversed /all normal etc.
    Adapters have a common ground, even if isolated
    from the mains with a transformer.

    India Broadband Forum
    Use MCB ( miniature circuit breakers) which will trip ,
    for short circuit etc. Specially when using Hair dryers/Water heaters/Mixies/grinders etc.
    Last edited by essbebe; 10th December 2010 at 05:14 PM.

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