Is it ok to attach an anti-static wrist band to mains earth?

Discussion in 'General Electronics Chat' started by timez82, Aug 13, 2011.

  1. timez82

    Thread Starter New Member

    Aug 13, 2011
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    Hi,

    I have brought an anti-static wrist strap - but i had nothing to earth it to in my room - so i attached a wire from mains earth (inside the mains outlet) to a screw on the wall - then attached the anti-static strap to the screw?

    Is this safe?! lol.

    the strap has a 1 Mega Ohm resister built in.

    Do i need another one on the wire to you think?

    Thank you

    Timez82
     
  2. hgmjr

    Moderator

    Jan 28, 2005
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    Usually I attach the ground strap (using the alligator clip) to a un-painted bare place on the chassis of the equipment on which I am working. That in turn is often attached to the safety ground from the AC mains provided the equipment is powered off of mains.

    That said I would think it permissible to connect your ground strap to the third wire safety ground on the mains plug. Before you do this you should use one of those outlet test plugs to make sure that the safety ground is properly wired back to your power distribution box.

    hgmjr
     
  3. timez82

    Thread Starter New Member

    Aug 13, 2011
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    lol i dont have one of those plugs - or can afford one before i start using the strap - is there anyway i can make one? or use a multimeter? or test it on the fusebox?

    Timez82
     
  4. hgmjr

    Moderator

    Jan 28, 2005
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    A proper ESD work station is not an easy thing to establish for the average hobbyist.

    Your best bet is to properly connect your ground strap to the bare metal of the chassis of the equipment you are servicing. That way whether your chassis is earth grounded or not you will be at the same potential as the PC boards you are handling.

    Handle the boards with care and reinstall them in the equipment when you are not working on them.

    hgmjr
     
  5. timez82

    Thread Starter New Member

    Aug 13, 2011
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    its not for pc's tho - its for learning electronics - closest i have to a chassi is a breadboard lol
     
  6. Wendy

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    Mar 24, 2008
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  7. someonesdad

    Senior Member

    Jul 7, 2009
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    The answer to the OP's original question is: yes, it is safe, providing a) you did really electrically connect it to the grounded conductor and b) the grounded conductor is in fact properly electrically connected to earth somewhere.

    Establishing that the grounded conductor is truly electrically connected to earth is typically not a trivial exercise. In a home, you have to verify that

    1. The grounding wire you're connecting to is in fact electrically connected to the grounding wires in the circuit breaker panel;
    2. The home's grounding rod is connected properly to the circuit breaker system;
    3. The ground rod's resistance to ground is low.
    A shortcut to these verification steps is to drive a metal rod into the ground outside and measure the resistance between the rod and your grounded conductor. A resistance on the order of an ohm is good and indicates a decent ground. But a higher resistance could mean either your temporary rod isn't well-connected to ground or your grounded conductor isn't really grounded well. (I'm going to be vague as to what a "higher resistance" is, as you'll need to do some research on the topic to find out when you should worry.)

    One of the checks you can do to verify your home's grounding rod is to measure its resistance to ground. This is often done by the fall of potential method. I've done it on my home's grounding rod (I used a DC power supply and my DMM, along with some 3/8" diameter galvanized spikes that I drove into the ground and some long wires) and it's not too hard to do (I measured 1.1 ohms for my grounding rod's resistance to earth); if you're interested in trying it, look up the method on the web.
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Every place I have worked used the AC ground to return the anti-static grounding items, meaning the straps, anti static mats, and the metal of the workbench all get returned to the AC line ground. This is even checked yearly to make sure it didn't fall off, a paper log is kept and saved a evidence we're really following procedure.

    We also keep a wrist band checker on hand. Every morning you are supposed to check your strap and wire and log the date and your initials. The device checks there is a high value of resistance so a low or high resistance will both fail.

    Not that you need to do all that, just sayin' it is standard proactive to use the AC ground. Keep in mind your project also needs to be connected to the ground or you could potentially zap it thru your protection equipment.

    If your strap wire has a clip on the end it is acceptable to clip that to what you are working on if no AC ground is available, but using ground is preferable as that gives a path for the static to "go away."
     
  9. timez82

    Thread Starter New Member

    Aug 13, 2011
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    some very interesting ideas - plus the testing it with metal rods is right up my street lol - i love all the hands on stuff :)

    thank you everyone.

    Timez82
     
  10. CraigHB

    Member

    Aug 12, 2011
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    The ground leg on utility wiring is normally connected to a ground rod near the utility panel so ideally, that should work as well as possible. The problem is that not all ground rods are installed correctly. I found this out when I wanted to add a ground rod for an antenna on my property.

    It's actually not a trivial task to properly install a ground rod. It needs to be fairly deep, at least 4 or 5 feet IIRC, and then the hole has to be treated with special materials beforehand.

    It's not cheap to have one installed correctly and there's no simple way to test a rod already installed. Installers may have specialized equipment to test rods, but I wouldn't know one way or the other.

    In any case, if you are in a building that is "up to code", you should be able to trust that utility power ground is a proper Earth ground.

    I also connect my body ground strap to utility power ground. Haven't had a problem yet.
     
  11. timez82

    Thread Starter New Member

    Aug 13, 2011
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    thanks lol :) yeah just didnt wanna zap myself lol
     
  12. timez82

    Thread Starter New Member

    Aug 13, 2011
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    what i did was wrap the wire round the wires inside the plug that go to earth (after taking them out of their hole) and then soldered my earth wire to them and installed them back into the plug as if it is one ground.
     
  13. someonesdad

    Senior Member

    Jul 7, 2009
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    I believe the typical ground rod depth in the US is around 8 feet deep (the last ground rod I bought was that long). As to testing, it is conceptually reasonably simple, at least via the "fall of potential" method -- any ham or experienced hobbyist can do it, as all it requires is a DC power supply, a digital multimeter, spikes, wire, and miscellaneous connectors. The pros have equipment that can help make the testing faster, but this stuff is priced out of the range of the typical hobbyist. Still, even the pros still use the fall of potential method, especially for larger power installations.

    Frankly, I would personally never trust any installation -- how do you know it's "up to code" unless you did the work yourself or was the inspector of the work? You're left to assume things are OK unless you verify things yourself.
     
  14. timez82

    Thread Starter New Member

    Aug 13, 2011
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    yeah thats very true - i know i shouldnt have but i installed my own electric cooker (it was really easy - even earth / live / neutral was marked on the cooker.

    When i checked the switch for it i found all the wires to be incredibly loose - almost like they were never screwed in, in the first place.

    Timez82
     
  15. MrChips

    Moderator

    Oct 2, 2009
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    My scope has a ground banana post. I plug my grounding strap into that.
     
  16. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Surprised that no one has mentioned using the screw that holds the cover plate on the outlet as the point/place to connect the ground strap. It is connected to the same metal stamping that makes up the mounting of the outlet and the actual ground opening in the receptacle. Its all one piece in the stamping of the outlet.

    Using that screw eliminates any chance of a connection to live when plugging into the receptacle and still allows both 'live' receptacles to be used.
     
  17. PeeSeeBee

    Member

    Jun 17, 2011
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    Don't know about the USA, but in the UK plastic boxes were sometimes used in the past. I have them in my house. The faceplate screws are completely isolated.
     
  18. russ_hensel

    Well-Known Member

    Jan 11, 2009
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    Make sure you understand the function of the 1 meg resistor. You want yourself at 0v with respect to ground, but you do not want to be a low impedance path to ground as that opens you up to fatal shock should you touch a place at the wrong potential and impedance.
     
  19. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Don't know about the UK but in the US the ground wire is hooked-up to a 'Green' screw that is part of the main body of the receptacle. The box is then grounded by the mounting of the receptacal to it, or not in the case of a plastic box. Its done this way to insure that the receptacle is part of the ground path, separate from the box. And the faceplate screw is screwed into that part of the receptacle.
     
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