Am I grounded or delusioned?

Discussion in 'General Electronics Chat' started by DanielK, Mar 11, 2009.

  1. DanielK

    Thread Starter New Member

    Mar 11, 2009
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    Hello everybody! My first time here, so hello once again :)

    I'm confused about grounding.

    Let's say that I'm statically charged from walking on a carpet or something like that.

    If I touch a long metal pipe, that is not connected to Earth, will I get discharged to ground level like if I touched a water faucet pipe or a radiator?

    Or am I only equalizing the potential level between my skin and the pipe?

    If it's the latter, what happens if I get charged again and touch the same pipe one more time?

    What if you connect your ESD wrist strap to the pipe, will it work in the same way, as if you connected it to a radiator pipe or outlet ground pin?

    Or does it have the same effect as not wearing the strap altogether and taking greater risk of damaging equipment?

    In other words, does it really have to be connected to a piece of metal dug into the ground to bleed off the charge, or any big piece of metal will do?

    Excuse my foolish questions :)

    My experience in electronic circuits is shallow, but I'm more than willing to learn.

    Daniel
     
  2. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    Actually, this is a very good question. Assuming the pipe has no path to ground, you will only be equalizing the charge.

    HOWEVER...the pipe, being a conductor, distributes the charge through the entire VOLUME of the metal, whereas the static charge you accumulated is only on the outside surface...basically ONE MOLECULE skin!

    The total charge capacity of a hunk of pipe is MANY MANY MANY orders of magnitude greater than the charge capacity of your carpet...so you'll be doing a LOT of walking to bring the surface charge of the pipe up to your "body" charge!
     
  3. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
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    I need to make one addition here. If you hold a key in your hand, you will find that it will appear to have the same kind of surface charge as your body...how can this be, since the key has significant mass?

    It takes some time for the surface charge on the key to "soak in" to the point where the charge is essentially negated. This "electron drift' process is actually fairly slow...not near the speed of light as the ENERGY flow is in a conductor. So, if you can ZAP a piece of metal numerous times in rapid succession, before the surface charge has time to penetrate the metal, you CAN build up a cumulative charge. (This is why Van-Degraffe generators can generate such a high charge on a metal sphere..but it goes away FAST!)

    Hope this helps.

    Eric
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Have you read the AAC book article on ESD?
     
  5. DanielK

    Thread Starter New Member

    Mar 11, 2009
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    So essentially, I was doing the works "unprotected" from ESD?
     
  6. beenthere

    Retired Moderator

    Apr 20, 2004
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    If the house/building has properly designed power distribution, the any metal surface you touch will have continuity with ground, and you will always be fully discharging yourself. In the case you mention where the pipe is not connected electrically to anything (but your static charge now and again), then the pipe will continue to accumulate charge.

    Google "van de graaf generator" to see the eventual outcome of that accumulation.
     
  7. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    A fun experiment I did with my kid was this:

    Wintertime, both had rubber soled shoes on shag carpet. Both of us slid our feet across the carpet to a metal desk.

    Our fingers could touch each other and no shock. If we both touched the desk, we both got a shock. If one touched the desk first, the other person's finger would then give a shock.

    He was fascinated, After an hour, my legs were tired, shoes were warm, and I couldn't get "Scotch Guard" out of my mind. :D

    He's been interested in electricity/electronics ever since.

    </oldmanreminiscing>
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    There is one proviso on this, city water, which is none too pure, is conductive. Somewhere (maybe very long away) there will be metal pipes in the earth. So it is a ground, of a sort. The problem is, over distance the earth is not at the same potential (just like clouds, hence lightening). You need a local ground to do the job right. Odd are water pipes will provide this, but it isn't guaranteed.

    To DanielK,

    Did you read the article I suggested? Just curious what you thought about it, since I wrote it.
     
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