when touch, get an Electric shock!!

Discussion in 'General Electronics Chat' started by ranatungawk, Feb 16, 2015.

  1. ranatungawk

    Thread Starter Senior Member

    Oct 30, 2008
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    0
    Hi friendz,

    I have noticed when some of 3rd party PC- Power supplies (Even the casing of the PC) is touched, we get an Electric shock!! can you please tell me how it happens ? Live of the primary side is shorted with the ground ??

    thanks
     
  2. bushrat

    Member

    Nov 29, 2014
    97
    22
    Is the chassis grounded properly?
     
  3. Reloadron

    Active Member

    Jan 15, 2015
    963
    232

    What he said. Is your mains power properly grounded? Is the computer properly grounded? Is the mains power polarity correct as in Hot, Neutral and Ground? Sounds like things are not properly grounded.

    Ron
     
  4. ranatungawk

    Thread Starter Senior Member

    Oct 30, 2008
    147
    0

    This is not a grounding issue ..! this must be a designing problem..coz, even though it's grounded or not, this problem can be seen on the power supplies of branded PCs.
     
  5. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    Looks like a problem with your house wiring.

    Get a voltmeter and measure the voltage between the chassis and true ground.
     
  6. ranatungawk

    Thread Starter Senior Member

    Oct 30, 2008
    147
    0

    Not at all, branded pc works fine there....and i'm saying about a common issue , this is not a issue for a specific PC, you can see this on most of Chinese made PC housing (see the following pic ) that are used for PC assembling !!

    P4_ATX_Computer_Case_C02.jpg
     
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Are you using a three-wire line-cord between your PC supply and the wall outlet?

    Do you have a three pin-plug in the wall or only two? If only two, what are you doing with the green wire that would be in the standard line cord.
     
  8. strantor

    AAC Fanatic!

    Oct 3, 2010
    4,302
    1,988
    Your logic is ass backwards dude.

    #1. This is a safety issue. There are a myriad of laws and standards imposed on manufacturers to keep them from making unsafe products. It is in their best interest to make computers that do NOT shock people.
    #2. Sure, it's possible a manufacturer could not care about laws and standards, and could make and sell a computer that shocks people. But they will not be in business for long. They will either be sued into the ground, or some government will shut them down, or word will get out and people will stop buying their products. It is much easier and smarter and more profitable to simply play by the rules and make safe products. If you're really convinced that several of these "branded" manufacturers are flying in the face of accepted practice and selling unsafe computers to you (and only you, apparently, you give no links to others complaining of the same), then you must be a conspiracy theorist.
    #3. 4 people, 3 of which are established experts on this forum and have undoubtedly seen this exact issue hundreds of times in the past, have told you that it's a grounding issue (which it is). But you continue to insist that it is a design flaw; or rather a common design flaw shared among multiple "branded" manufacturers. If you are smarter than everybody here and you already know the answer to your question, why bother asking?

    Give up your conspiracy theory and check your house ground.
     
    tom_s, JohnInTX, #12 and 3 others like this.
  9. panic mode

    Senior Member

    Oct 10, 2011
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    according to Google, Sri Lanka has two standards, old Europlug (CEE7/16 which is not grounded) and Indian BS-546.
    which one you are using and how does your power connection to AC outlet look like (any adapters?)?

    I can see few potential issues:
    - you are using wrong cable or extension cord or some adapter which does not use GND
    - your house wiring is not up to todays standard (outlets are not grounded) or it is faulty
    - grounding is not really issue after all and you get static zap like from walking on carpet using dry footware that has no ESD sole. same happens when you approach and touch car. this will only give you momentary zap so touching again will cause no further zaps.

    if it is one of the first two issues, you have to address them asap.
     
  10. MrChips

    Moderator

    Oct 2, 2009
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    The TS did not elaborate on what "Electric shock" he is experiencing.
    Is it a momentary ESD discharge or is it continuous when the PC is touched?

    I would assume that they do not experience ESD in Sri Lanka on account of the high humidity.
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    If there's no earth connection; the mains input filter capacitors basically form a capacitive potential divider across the mains - with all the metal case connected to the mid point.

    The capacitors are very small (usually not much more than 470pF or so) the current is tiny and you'd have to be a bit of a wuss to be bothered by it.

    It can be a bit of a problem on stacks of TV, DVD, VCR and various assorted set top boxes, all connected together by chassis potential scart leads - can add up to a lot of mains input filter capacitors in parallel.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Do you have a state accredited service where you are? I watched a documentary a while back that showed many electrical installations in India are effected by bribes etc, and do not actually conform to any safety standard.
    I am not sure if the same applies to Sri-Lanka, and do not wish to cast any aspersions on anyone.
    But I had to ask.
    As mentioned, PC power supplies should have a ground wire connected to earth ground, this also includes the output, DC side also, of which the supply common is connected to earth ground.
    Max.
     
  13. Lundwall_Paul

    Member

    Oct 18, 2011
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    19
    I remember when I was a kid it was common to get shocks off of the TV. This was well before polarized plugs and one side of the AC input was tied to chassis.
     
    shortbus likes this.
  14. ian field

    Distinguished Member

    Oct 27, 2012
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    A few decades ago, almost all TVs, radios etc were AC/DC and live chassis. In the very early days, some people were still using a light socket adapter, non-polarised 2 pin plugs persisted a lot longer.

    Plastic control spindles were only just (very slowly) starting to appear, so if one of the knobs fell off and you were leaning against a radiator and get hold of a live metal spindle - that was it!

    Even when SMPSUs became commonplace, there were still live chassis, one of the Bush/Rank/Murphy CTVs had a true inverter SMPSU - the chassis was at a dangerous negative potential rather than having a positive HT.

    The introduction of scart sockets pretty much forced the isolated secondary SMPSU - it was probably a bigger life saver than anything.
     
    Lundwall_Paul likes this.
  15. Reloadron

    Active Member

    Jan 15, 2015
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    Ian, while I can't speak for across the pond a few decades ago all the TVs and radios I remember had a two wire plug sans ground. They were noy AC/DC but strictly AC. Those two wires went through an On/Off switch (or at least one of them did) to a transformer which had several secondaries. The primary was 120 VAC or back then commonly called 110 VAC and the secondary was 5 VAC for a 5u4 or 5Y3 HV rectifier tube (or valve for those on the other side of the pond) plus the HV for the tube plates and 6.3 and 12.6 VAC for the filaments. I also got well acquainted with a hot chassis on many occasion standing bare footed on a basement concrete floor and touching a chassis that was plugged in the wrong way. :)

    Ron
     
  16. MaxHeadRoom

    Expert

    Jul 18, 2013
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    Many Like my mother used the iron this way, handling damp clothes, 240vac to boot, OK if you wore rubber soled shoes!:eek:
    Max.
     
  17. ian field

    Distinguished Member

    Oct 27, 2012
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    British set makers were way ahead of their US counterparts in saving the cost and weight of a mains transformer.

    We had the Pxxnnn family of valves with 300mA heaters for series chains, there was also 100mA family for record players and low end radios.

    The US had a 600mA family of valves, but I think it lasted a much shorter period of time before valves were phased out.

    In various magazine archives, from time to time I find references/schematics for American valves with heaters nominally rated for the full mains voltage.

    The situation was a little different in Britain, power stations could pop up anywhere with either DC or AC, there was no standardisation on voltage or frequency, so 2, 4 or 6V accumulators remained popular for heater supplies for a long time.

    Aren't market forces wonderful!
     
  18. MaxHeadRoom

    Expert

    Jul 18, 2013
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    I believe it was the same in N.A., before the Grid, large establishments had a local generator, often initially DC as only lighting was involved.
    In the process of acquiring my electrical qualifications, one of my first assignment's was converting the old Oxford University Observatory from a Edison 110v DC Generator system to the UK 240v grid.
    Max.
     
  19. ian field

    Distinguished Member

    Oct 27, 2012
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    The AC/DC debate in America was largely decided by old-sparky.
     
  20. wayneh

    Expert

    Sep 9, 2010
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    Ironically, yes. A great example of the Law of Unintended Consequences.
     
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