anti-static/grounding question...

Discussion in 'NZ Computing' started by gimp, Jan 3, 2006.

  1. gimp

    gimp Guest

    every motherboard manual i've read says when doing a system build the
    power cable should be unplugged to avoid electric shock.... but
    seriously if its switched off at the wall there's no danger - is that
    correct...? also does touching the PSU still work as a ground if the
    cable is unplugged..?
     
    gimp, Jan 3, 2006
    #1
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  2. gimp

    Shane Guest

    On Tue, 03 Jan 2006 20:42:04 +1300, gimp wrote:

    > every motherboard manual i've read says when doing a system build the
    > power cable should be unplugged to avoid electric shock.... but seriously
    > if its switched off at the wall there's no danger - is that correct...?


    as long as someone else doesnt switch it on behind you
    Theres a big debate on this issue, on the one hand some people say the
    power cable provides an excellent earth
    OTOH people say its too easy for a faulty switch to be on, or someone else
    switch it live without your knowledge to make it safe
    Its your risk..

    > also does touching

    the PSU still work as a ground if the cable is
    > unplugged..?




    --
    An empty cab drove up and Sarah Bernhardt got out. -Arthur Baer,
    American comic and columnist
     
    Shane, Jan 3, 2006
    #2
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  3. gimp

    Rob J Guest

    In article <dpd9mk$836$>, says...
    > every motherboard manual i've read says when doing a system build the
    > power cable should be unplugged to avoid electric shock.... but
    > seriously if its switched off at the wall there's no danger - is that
    > correct...? also does touching the PSU still work as a ground if the
    > cable is unplugged..?


    Any electrician will tell you not to rely on the mains earth as being a
    true earth and totally safe. A wiring fault in a building could result
    in the earth voltage being jacked up well above zero.

    Having said that - everyone regards the mains earth as safe when working
    on PCs.

    Touching the metal case does not work as a ground if there is no
    physical connection from the case to ground.

    The power supply itself is working with mains voltages within, you
    should not open the case of the power supply with the mains connected.
    Also be aware that most modern boards are still powered even when the PC
    is "off" as they are able to be woken up by system events. Mains power
    should be switched off at the wall when working on these PCs.
     
    Rob J, Jan 3, 2006
    #3
  4. gimp

    XP Guest

    On Tue, 03 Jan 2006 20:42:04 +1300, gimp <> wrote:

    >every motherboard manual i've read says when doing a system build the
    >power cable should be unplugged to avoid electric shock.... but
    >seriously if its switched off at the wall there's no danger




    Yes there is as it can be switched back on again.

    With the Plug out its 100 % Safe.

    I worked on Power distribution boards in the UK, when we wished to disable a
    circuit we removed the Fuses and placed them in our overalls, so no one could
    plug them back in..


    >- is that
    >correct...? also does touching the PSU still work as a ground if the
    >cable is unplugged..?
    >




    Get a earth strap from DSE, then you do not forget..
     
    XP, Jan 3, 2006
    #4
  5. On Tue, 03 Jan 2006 20:42:04 +1300, gimp <> wrote:

    >every motherboard manual i've read says when doing a system build the
    >power cable should be unplugged to avoid electric shock.... but
    >seriously if its switched off at the wall there's no danger - is that
    >correct...? also does touching the PSU still work as a ground if the
    >cable is unplugged..?


    I always work on my PC with the mains cable in, but the wall switch
    off, in order to retain an earth connection. If it is not plugged in,
    then there will be no earth. I always use a DSE earthing strap - it
    is much safer than trying to remember to ground yourself at crucial
    times. I consider it pretty safe to work like this as long as I am
    not trying to work on the inside of the power supply - when you open
    the power supply case, you are exposing high voltage wiring and
    *really* need the assurance of unplugging from the wall.

    The voltages on the outside of the power supply are not at all
    dangerous to a human, as long as the power supply has not suffered a
    catastrophic fault that allows the high voltages through it into the
    PC, so your real danger if someone turns the power on is firstly that
    you will damage your PC and secondly that the fans will catch a bit of
    you or your clothing.

    If you are leaving the plug in, make sure that where you are working
    on the PC has the plug in your field of view, so no-one can turn it on
    again without you noticing. If you can not do that, put parcel tape
    over the switch and label it with a marker pen: "DO NOT TURN ON!" and
    your name.
     
    Stephen Worthington, Jan 3, 2006
    #5
  6. gimp

    EMB Guest

    Stephen Worthington wrote:

    > If you are leaving the plug in, make sure that where you are working
    > on the PC has the plug in your field of view, so no-one can turn it on
    > again without you noticing. If you can not do that, put parcel tape
    > over the switch and label it with a marker pen: "DO NOT TURN ON!" and
    > your name.


    Make up a short extension lead with only an earth conenction and plug
    the PC in via that - then there's no chance of a faulty switch leaving
    power on the PC.

    --
    EMB
     
    EMB, Jan 3, 2006
    #6
  7. gimp

    Rob J Guest

    In article <>,
    34.nz56.remove_numbers says...
    > On Tue, 03 Jan 2006 20:42:04 +1300, gimp <> wrote:
    >
    > >every motherboard manual i've read says when doing a system build the
    > >power cable should be unplugged to avoid electric shock.... but
    > >seriously if its switched off at the wall there's no danger - is that
    > >correct...? also does touching the PSU still work as a ground if the
    > >cable is unplugged..?

    >
    > I always work on my PC with the mains cable in, but the wall switch
    > off, in order to retain an earth connection. If it is not plugged in,
    > then there will be no earth. I always use a DSE earthing strap - it
    > is much safer than trying to remember to ground yourself at crucial
    > times. I consider it pretty safe to work like this as long as I am
    > not trying to work on the inside of the power supply - when you open
    > the power supply case, you are exposing high voltage wiring and
    > *really* need the assurance of unplugging from the wall.
    >
    > The voltages on the outside of the power supply are not at all
    > dangerous to a human, as long as the power supply has not suffered a
    > catastrophic fault that allows the high voltages through it into the
    > PC, so your real danger if someone turns the power on is firstly that
    > you will damage your PC and secondly that the fans will catch a bit of
    > you or your clothing.
    >
    > If you are leaving the plug in, make sure that where you are working
    > on the PC has the plug in your field of view, so no-one can turn it on
    > again without you noticing. If you can not do that, put parcel tape
    > over the switch and label it with a marker pen: "DO NOT TURN ON!" and
    > your name.


    I made a special mains cable with only the earth pins connected both
    ends.
     
    Rob J, Jan 3, 2006
    #7
  8. gimp

    Bruce Knox Guest

    On Tue, 3 Jan 2006 21:22:19 +1300, Rob J <> wrote:

    >In article <dpd9mk$836$>, says...
    >> every motherboard manual i've read says when doing a system build the
    >> power cable should be unplugged to avoid electric shock.... but
    >> seriously if its switched off at the wall there's no danger - is that
    >> correct...? also does touching the PSU still work as a ground if the
    >> cable is unplugged..?

    >
    >Any electrician will tell you not to rely on the mains earth as being a
    >true earth and totally safe. A wiring fault in a building could result
    >in the earth voltage being jacked up well above zero.

    Not a problem in this case. A suitable earth for anti static can be
    100MOhm and work fine. In fact most professional anti static eaths
    will incorporate such a resistance so they earth static charges but do
    not provide a high current earth if you touch a dangerous high voltage
    source. Likewise it does not matter if the earth is above true earth.
    You are trying to minimise voltage differentials. If the case is at 30
    volts then everything should be at 30 volts.

    On all pcs I have seen unless you are working on the power supply (a
    sealed system) there is no way of contacting dangerous voltages. My
    advise is to leave it plugged in but switched off to get the earth.
    Touching the case when it is not earthed is no protection from static
    charges.
    ....


    Bruce http://www.baggins.co.nz
    http://physio.otago.ac.nz
     
    Bruce Knox, Jan 3, 2006
    #8
  9. gimp wrote:
    > every motherboard manual i've read says when doing a system build the
    > power cable should be unplugged to avoid electric shock.... but
    > seriously if its switched off at the wall there's no danger - is that
    > correct...? also does touching the PSU still work as a ground if the
    > cable is unplugged..?


    I don't see any advantage in grounding the machine to mains earth while
    building a system, in fact this will improve the chances of damage from static
    electricity as the path to ground for the static will be improved.

    In the absence of a grounding strap keeping skin touching a metallic part of
    the case is better than nothing but the closer you get to an antistatic
    workstation the fewer random deaths you will suffer.

    The idea is to keep you, the machine and all the components you are putting
    into it close to the same voltage.

    If you earth yourself to the case of the machine with a grounding strap, you
    still need to consider how you handle components you are installing into the
    machine. Touching something that's not earthed when you are doesn't protect
    that thing from static electricity that it may be carrying and which may
    discharge through you to earth. That's why commercial antistatic workstations
    include a mat for the work surface.
     
    Mark Robinson, Jan 3, 2006
    #9
  10. gimp

    Rob J Guest

    In article <>,
    says...
    > On Tue, 3 Jan 2006 21:22:19 +1300, Rob J <> wrote:


    > >Any electrician will tell you not to rely on the mains earth as being a
    > >true earth and totally safe. A wiring fault in a building could result
    > >in the earth voltage being jacked up well above zero.

    > Not a problem in this case. A suitable earth for anti static can be
    > 100MOhm and work fine. In fact most professional anti static eaths
    > will incorporate such a resistance so they earth static charges but do
    > not provide a high current earth if you touch a dangerous high voltage
    > source. Likewise it does not matter if the earth is above true earth.
    > You are trying to minimise voltage differentials. If the case is at 30
    > volts then everything should be at 30 volts.


    If you touch this and something that is at true earth you get zapped.

    > On all pcs I have seen unless you are working on the power supply (a
    > sealed system) there is no way of contacting dangerous voltages.


    Only true of ATX and later designs.

    Earlier PCs often had a front panel 230V power switch with mains wiring
    between it and the power supply.
     
    Rob J, Jan 3, 2006
    #10
  11. gimp

    Richard Guest

    Mark Robinson wrote:

    > If you earth yourself to the case of the machine with a grounding strap,
    > you still need to consider how you handle components you are installing
    > into the machine. Touching something that's not earthed when you are
    > doesn't protect that thing from static electricity that it may be
    > carrying and which may discharge through you to earth. That's why
    > commercial antistatic workstations include a mat for the work surface.


    Which is why the sealed antistatic bag should be placed on the static
    worksurface, and opened on it and then the contents placed on it. The bag will
    charge/discharge the contents uniformly and safely to the potential of the
    worksurface.

    The static work surface should be at the same potential as the computer that you
    are also working on, this doesnt have to be the ground ground, but its usual
    that it is since the computers going to be plugged in at some stage.
     
    Richard, Jan 3, 2006
    #11
  12. gimp

    XP Guest

    On Tue, 03 Jan 2006 10:25:09 GMT, Stephen Worthington
    <34.nz56.remove_numbers> wrote:

    >On Tue, 03 Jan 2006 20:42:04 +1300, gimp <> wrote:
    >
    >>every motherboard manual i've read says when doing a system build the
    >>power cable should be unplugged to avoid electric shock.... but
    >>seriously if its switched off at the wall there's no danger - is that
    >>correct...? also does touching the PSU still work as a ground if the
    >>cable is unplugged..?

    >
    >I always work on my PC with the mains cable in, but the wall switch
    >off, in order to retain an earth connection. If it is not plugged in,
    >then there will be no earth. I always use a DSE earthing strap - it
    >is much safer than trying to remember to ground yourself at crucial
    >times. I consider it pretty safe to work like this as long as I am
    >not trying to work on the inside of the power supply - when you open
    >the power supply case, you are exposing high voltage wiring and
    >*really* need the assurance of unplugging from the wall.
    >
    >The voltages on the outside of the power supply are not at all
    >dangerous to a human, as long as the power supply has not suffered a
    >catastrophic fault that allows the high voltages through it into the
    >PC, so your real danger if someone turns the power on is firstly that
    >you will damage your PC and secondly that the fans will catch a bit of
    >you or your clothing.
    >
    >If you are leaving the plug in, make sure that where you are working
    >on the PC has the plug in your field of view, so no-one can turn it on
    >again without you noticing. If you can not do that, put parcel tape
    >over the switch and label it with a marker pen: "DO NOT TURN ON!" and
    >your name.





    YOU DO NOT NEED A EARTH CONNECTION WHEN WORKING ON A PC AND MOBO, YOU JUST
    NEED A ANTI STATIC STRAP.


    ITS THE POTENAL DIFFERENCE BETWEEN YOU AND THE COMPUTER CASE THAT MATTERS..
     
    XP, Jan 3, 2006
    #12
  13. gimp

    XP Guest

    On Wed, 04 Jan 2006 00:02:15 +1300, Mark Robinson <2tod.net>
    wrote:

    >gimp wrote:
    >> every motherboard manual i've read says when doing a system build the
    >> power cable should be unplugged to avoid electric shock.... but
    >> seriously if its switched off at the wall there's no danger - is that
    >> correct...? also does touching the PSU still work as a ground if the
    >> cable is unplugged..?

    >
    >I don't see any advantage in grounding the machine to mains earth while
    >building a system, in fact this will improve the chances of damage from static
    >electricity as the path to ground for the static will be improved.
    >
    >In the absence of a grounding strap keeping skin touching a metallic part of
    >the case is better than nothing but the closer you get to an antistatic
    >workstation the fewer random deaths you will suffer.
    >
    >The idea is to keep you, the machine and all the components you are putting
    >into it close to the same voltage.
    >
    >If you earth yourself to the case of the machine with a grounding strap, you
    >still need to consider how you handle components you are installing into the
    >machine. Touching something that's not earthed when you are doesn't protect
    >that thing from static electricity that it may be carrying and which may
    >discharge through you to earth. That's why commercial antistatic workstations
    >include a mat for the work surface.






    Totally correct..
     
    XP, Jan 3, 2006
    #13
  14. gimp

    XP Guest

    On Wed, 04 Jan 2006 00:19:03 +1300, Richard <> wrote:

    >Mark Robinson wrote:
    >
    >> If you earth yourself to the case of the machine with a grounding strap,
    >> you still need to consider how you handle components you are installing
    >> into the machine. Touching something that's not earthed when you are
    >> doesn't protect that thing from static electricity that it may be
    >> carrying and which may discharge through you to earth. That's why
    >> commercial antistatic workstations include a mat for the work surface.

    >
    >Which is why the sealed antistatic bag should be placed on the static
    >worksurface, and opened on it and then the contents placed on it. The bag will
    >charge/discharge the contents uniformly and safely to the potential of the
    >worksurface.
    >
    >The static work surface should be at the same potential as the computer that you
    >are also working on, this doesnt have to be the ground ground, but its usual
    >that it is since the computers going to be plugged in at some stage.




    The biggest problem with putting in a MoBo is shorting the CMOS battery to
    other logic parts, the 3v battery can blow up IC's


    Is far better to remove it and wait a few minuets for the CMOS circuit to
    discharge its self.
     
    XP, Jan 3, 2006
    #14
  15. On Wed, 04 Jan 2006 00:19:03 +1300, Richard <> wrote:

    >Mark Robinson wrote:
    >
    >> If you earth yourself to the case of the machine with a grounding strap,
    >> you still need to consider how you handle components you are installing
    >> into the machine. Touching something that's not earthed when you are
    >> doesn't protect that thing from static electricity that it may be
    >> carrying and which may discharge through you to earth. That's why
    >> commercial antistatic workstations include a mat for the work surface.

    >
    >Which is why the sealed antistatic bag should be placed on the static
    >worksurface, and opened on it and then the contents placed on it. The bag will
    >charge/discharge the contents uniformly and safely to the potential of the
    >worksurface.
    >
    >The static work surface should be at the same potential as the computer that you
    >are also working on, this doesnt have to be the ground ground, but its usual
    >that it is since the computers going to be plugged in at some stage.


    If you do not have a static mat, the next best thing is to put the
    gear down in its bag on the metal PC chassis so it can ground itself.
    Give it a couple of seconds, then, wearing your grounding strap
    connected to the PC chassis, you can safely pick it up again and open
    the bag to install what is inside. I like the way my server case
    works for this - it has bare metal at the top when upright with the
    covers off, great for putting things down on. My workstation case has
    a painted top when I have the side covers off - not a good earth - so
    I normally lay it down on its side to work on it so I don't forget and
    put things on the top.
     
    Stephen Worthington, Jan 3, 2006
    #15
  16. gimp

    Don Hills Guest

    In article <2tod.net>,
    Mark Robinson <2tod.net> wrote:

    .... the best advice given so far in this thread. I won't requote it, but I
    will summarise it. This is relevant to home workers, I would hope someone
    doing it for a living would have all the right kit and would know how to use
    it.

    Unplug the mains lead from the wall. No exceptions. Most modern PCs have 5
    volts present on the motherboard even when powered off - this is to run the
    "wake on LAN, wake on ring, wake on alarm" functions. It's not always the
    case, but making no exceptions ensures no problems. The 5 volts isn't
    dangerous to you, but shorting it out may damage the motherboard.

    Do not get hung up on trying to keep the PC at earth potential while working
    on it. What is important is to keep the PC, you, and all parts being changed
    at the same potential and, hopefully, close to earth potential.

    An anti-static strap is a good idea for those who have not learned to keep
    one hand (or arm, or wrist etc) on the chassis at all times. The machine
    itself usually provides a sufficiently large work area for placing parts
    being removed or replaced. Lay tower machines on their side. If you need
    more room, a sheet of tinfoil laid with one end under the machine in contact
    with bare metal will work fine. Obviously a true antistatic work mat would
    be ideal but they aren't cheap and for some reason there's never one around
    when you need one.

    Never open an antistatic bag unless it is lying on the machine or antistatic
    work surface. If you pick it up to open it, hold it back down on the machine
    as you withdraw the part. Never place unprotected parts down anywhere other
    than on the machine or work surface until they have been rebagged.

    If you have to leave the machine and come back, reattach your antistatic
    strap or touch the metal frame well away from any loose parts before
    continuing. If you're working in a bad environment where simply walking
    across the carpet causes you to draw sparks from door handles etc, find
    something handy to touch that will discharge you before touching the machine
    such as a water tap, concrete floor, metal window frame etc.

    --
    Don Hills (dmhills at attglobaldotnet) Wellington, New Zealand
    "New interface closely resembles Presentation Manager,
    preparing you for the wonders of OS/2!"
    -- Advertisement on the box for Microsoft Windows 2.11 for 286
     
    Don Hills, Jan 3, 2006
    #16
  17. gimp

    Bruce Knox Guest

    On Wed, 4 Jan 2006 00:11:09 +1300, Rob J <> wrote:

    ....
    >> source. Likewise it does not matter if the earth is above true earth.
    >> You are trying to minimise voltage differentials. If the case is at 30
    >> volts then everything should be at 30 volts.

    >
    >If you touch this and something that is at true earth you get zapped.

    Which you would just by touching the case. No need to open it up. Does
    not happen very often as if the electrical earth is elevated then the
    whole area is. Specially in a house built since full electrical earth
    bonding has been a requirement.
    >
    >> On all pcs I have seen unless you are working on the power supply (a
    >> sealed system) there is no way of contacting dangerous voltages.

    >
    >Only true of ATX and later designs.
    >
    >Earlier PCs often had a front panel 230V power switch with mains wiring
    >between it and the power supply.

    True. I forgot about the bad old days. In theory you need at least an
    electrical service technicians certificate to even open one of those
    cases (if it is your job).

    Bruce http://www.baggins.co.nz
    http://physio.otago.ac.nz
     
    Bruce Knox, Jan 3, 2006
    #17
  18. gimp

    gimp Guest

    Don Hills wrote:
    > Unplug the mains lead from the wall. No exceptions. Most modern PCs have 5
    > volts present on the motherboard even when powered off - this is to run the
    > "wake on LAN, wake on ring, wake on alarm" functions.



    i've used the wake-on functions before but IME they only work when the
    PSU is at on (i don't mean the pc switched on, i mean the lil' on/off
    switch at the back of the PSU), and the power is on at the wall.

    i've had no problems when grounding with the case but i think i will get
    an anti-static strap to make life easier :)
     
    gimp, Jan 3, 2006
    #18
  19. gimp

    whoisthis Guest

    In article <dpd9mk$836$>, gimp <>
    wrote:

    > every motherboard manual i've read says when doing a system build the
    > power cable should be unplugged to avoid electric shock.... but
    > seriously if its switched off at the wall there's no danger - is that
    > correct...? also does touching the PSU still work as a ground if the
    > cable is unplugged..?


    So far all I have read is bullshit from everyone else.

    Fact: Your body can build up a static charge of tens of thousands of
    volts, and higher. The fact that this is a static charge means that
    there is little energy (joules) involved so you will not kill yourself
    with this charge, but it can make someone jump when you touch them.

    Fact: When you body has a high static charge you do not even need to
    touch some components for damage to be done. There is "soft" damage
    which will not instantly kill a component, but will cause it to fail
    1-12 months later. Want proof of this, then think back to when you were
    a kid and remember how you could pick up bits of paper with a comb after
    brushing your hair.

    Fact: The semiconductors are now being built with much smaller
    dimensions, down to 65nm. Human hair diameters range from 40 microns to
    120 microns, ie about 1,000 time greater. 1nm is 1 billionth of a meter.
    This means that a voltage of 65v as an equivalent volts/meter of 1
    MILLION volts/meter. If you have a static charge of 65,000 volts that
    would have the equivalent volts per meter of 65 BILLION volts per meter.
    now then Voltage in a cloud-to-ground strike is 100 million to 1 billion
    volts.

    Fact: A proper earth strap should have an integrated resistor built into
    it, this is FAR safer than just touching the case. Last thing you want
    is to accidentally be earthed via zero ohms and touch something
    connected to the mains.

    Fact : You should work off an earthing mat too. Some places even have
    special antistatic flooring too.

    Fact : Too many "pc service people" do NOT take adequate protections,
    there are some companies that I would NEVER take anything to because
    they are lax with precautions.



    go here to read more

    http://www.semiconductors.philips.com/acrobat_download/various/IC26_CHAPT
    ER_3_2000.pdf

    and here
    http://assets.zarlink.com/AN/esd3.pdf

    and here

    http://www.marktechopto.com/pdfs/ESDPrecautions.PDF
     
    whoisthis, Jan 3, 2006
    #19
  20. gimp

    ~misfit~ Guest

    gimp wrote:
    > Don Hills wrote:
    >> Unplug the mains lead from the wall. No exceptions. Most modern PCs
    >> have 5 volts present on the motherboard even when powered off - this
    >> is to run the "wake on LAN, wake on ring, wake on alarm" functions.

    >
    >
    > i've used the wake-on functions before but IME they only work when the
    > PSU is at on (i don't mean the pc switched on, i mean the lil' on/off
    > switch at the back of the PSU), and the power is on at the wall.
    >
    > i've had no problems when grounding with the case but i think i will
    > get an anti-static strap to make life easier :)


    Yeah, not all PSUs have an on/off switch.
    --
    ~misfit~
     
    ~misfit~, Jan 3, 2006
    #20
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