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Before opening a computer, I often hear advice to touch something that is "grounded" - a computer case for example, or a heating element - to avoid damaging the sensitive electronic equipment through static discharge.

What exactly is true here, and what are the do's and don'ts.

  • Touching what objects will actually work, and what won't? If I touch a computer case, does it matter what it stands on, and whether it is connected to an outlet? What other ways are there to protect the equipment from a static discharge than touching something grounded?

  • Are there common pieces of clothing that I shouldn't be wearing when working inside a computer, for example a woollen pullover?

There is a lot on Google, but there seem to be many contradictions and misconceptions out there, so I think this is a question worth having here.

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I touch anything metal, If I move around much, I touch metal again, lucky for me my workbench is part metal. –  Moab Jan 25 '11 at 17:56
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Related question: superuser.com/q/71326/36601 –  AndrejaKo Jan 25 '11 at 19:04
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If anyone doubts the seriousness of ESD, I've killed 2 mice and a PS2 controller with ESD, and I was just touching them through normal use. I'm always super cautious when I'm actually inside something. –  Tofystedeth Jan 25 '11 at 22:54
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@Moab - surely touching something metal doesn't help that much unless that metal is grounded? These days, we're told absolutely never to leave the PC plugged in (but powered off) so the case itself is a suitable ground, the reason being that if the power supply is faulty you could be killed. Sounds odd to me - if that were the case, you'd probably be killed plugging in a USB lead, since all that back-of-the-PC stuff is bare metal. It's not so convenient, but working near a radiator works - so long as there's enough bare metal to touch. –  Steve314 Jan 26 '11 at 15:02
    
@ Steve314, Surely I do it all the time, my desk is not "grounded" and I discharge on it all the time (I get shocked). Everything is grounded, its only a question of how well it is grounded, and when it comes to a high voltage static charge, it does not have to be as good of a ground as you think. –  Moab Jan 26 '11 at 17:03
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6 Answers

up vote 18 down vote accepted

Touching any conductive material that is grounded will also ground you. As long as you are using a 3-prong outlet, your metal case should be grounded through the third (round) prong. You can also touch water pipes, metal conduit, or another person, though none of these are guaranteed to be grounded.

Any loose, woollen, or static-generating clothing should be avoided. Metal armor, though providing an excellent ground, should also be avoided. If you are really concerned about cleanliness, you could also avoid any clothing that will generate a lot of lint. This usually isn't a big deal, though.

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Good info, thanks. So the case needs to be connected to an outlet to be grounded, correct? It will not work if it is not connected? –  Pekka 웃 Jan 25 '11 at 17:49
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... But the socket switch can (and should!) be in the off position, it'll still be grounded. –  Sirex Jan 25 '11 at 18:26
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Yes and no. To ground the case, you need it to be connected, and to ground yourself you then touch the case, but you don't actually need the case or yourself to be grounded - merely to be at the same potential as the rest of the machine (so that no charge will move between you and the machine when you touch it somewhere sensitive). Touching a grounded part of the case does that - equalises the potential - whether or not the machine is grounded. –  Scott Jan 25 '11 at 18:26
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This answer is brilliant. +1 for mentions of metal armor and nudity. Useful and entertaining. –  Jeshii Jan 25 '11 at 22:49
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You're also assuming the "electrician" who wired your house up actually connected the 3rd prong to ground. I know many houses have these 3rd prongs for "decoration". –  Jeff Lamb Jan 25 '11 at 23:40
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The problem is that your body can store a lot of electrical energy, enough to blow components in an electrical circuit.

The answer is touching any metal part of your PC will put you and the PC at the same potential so removing the risk of damaging components...you don't have to be 'earthed'. Just remove the potential difference between you and the PC.

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If you have a proper dedicated workspace, the best approach is to get some proper anti-static mats to work on, these should be properly grounded and will have fittings for wrist straps etc, then when you lay the PC you're working on on the mat, it too will be grounded and therefore equalised.

If not, then I would suggest using both a wrist strap clipped to the case and grounding the machine using it's power lead. In order to reduce the danger suggested by Linker3000, make sure you use a proper RCD - These have been a compulsory fitment on all new electrical installations here in the UK for the last couple of years (although I don't know if that is the case in other countries), and you can also buy small plug-in ones to isolate individual appliances. Individual RCDs are also useful if you have a suspect bit of equipment and don't want to risk tripping the main circuit - But obviously don't play around inside mains kit without appropriate training!

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1) unplug your computer;

2) touch the case;

3) don't pet any cats, rub your hair on an inflated balloon, drag feet on carpet while you do your work.

If you want ultra-high ESD protection, get a grounding strap and attach to case.

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...all as long as the PSU is still connected to the mains (actually with no earth/ground in the US, I'm not sure how that'll even work). –  paradroid Jan 26 '11 at 0:12
    
@paradroid "actually with no earth/ground in the US" what? –  AttackingHobo Jan 26 '11 at 2:12
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Of course you have ground in the US. Theres this round pin coming from the cable :) aside from the two flat ones. –  sinni800 Jan 26 '11 at 15:38
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One word: Humidity.

If you want to know why, read up on static electricity. Initially grounding yourself will neutralize any static that you are carrying, but if you have a very dry atmosphere you can easily pick it back up again with just normal activity --- humidity helps prevent static electricity from building up by allowing it to bleed off into the atmosphere without having to be suddenly discharged. (Why? Because humidity makes the air a conductor.)

That's why you experience more static electricity discharges in the winter time, when the furnace is running (and there is no humidifier present, and there is nothing else present to introduce humidity).

If you have a more than passing interest as to why, start by reading the article at Wikipedia, which is a good starting point to more full-bodied research.

Having a wrist strap that keeps you connected to a ground all the time works, as well, if you cannot increase the humidity of your environment to a sufficient level (30% - 40%, which happens to also be optimal for human comfort and to keep things like paint from cracking on walls, seems to work well in my personal experience).

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Good point - humidity management is used for static control too in some circumstances, but not practical as an option for a field engineer, although one student on an A+ Service technician training course (which covers ESD protection), did suggest he could work on his home computer in his bathroom after a hot shower - which would also cover (or uncover!?) the clothing angle. –  Linker3000 Jan 26 '11 at 7:07
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Best practice is to NOT leave equipment plugged in and switched off to give you a grounded surface because when you touch or hold on to this to ground yourself YOU HAVE NO CURRENT LIMITING SAFETY DEVICE in the circuit between yourself and ground, so if you do touch a live part (maybe the PSU is faulty and the outlet power switch has been wired in the non-hot line) - even perhaps something nearby like a faulty desk lamp or the printer that actually has the fault (and has blown up the PC), you do not experience a hand-to-hand fault current to ground, which is VERY DANGEROUS because the fault path is via your heart. This is why engineers who have to work on (high voltage) live equipment are supposed to keep one hand in a pocket - it stops them from getting a shock from the hand holding the screwdriver to the hand touching the equipment chassis; instead, they get a jolt down the leg which can flippin' hurt, but is less likely to kill them.

ESD/Antistatic Wrist Strap Bonding plug

Proper use of the wrist strap (above left) is to either connect it to a grounding point (above right) to drain away any static you have generated OR to the metal chassis of the kit you are working on BUT the kit is still NOT grounded via a power cord and you are just using the strap for charge equalisation.

If you do not have the proper grounding wrist strap with safety resistor or an antistatic kit/workbench, just use the charge equalisation technique that Scott mentioned (with the equipment totally disconnected from the power outlet) OR just briefly touch a grounded metal pipe or connector and then work on the kit without holding onto anything grounded.

With regards to clothing, working naked is best but this may upset your friends/customers. Natural grown fibres/materials are next best - cotton or linen, but not wool or silk - so engineers that turn up in white cotton T-shirts and denim jeans with leather-soled shoes may look a tad casual but are less likely to be a walking static bomb. If you have to preserve a corporate appearance in front of your customers, a polyester suit may look the biz but may help you zap their server.

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Excellent answer. Thanks. May have to get myself one of those wrist straps. –  Pekka 웃 Jan 25 '11 at 20:06
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If I get arrested after trying out your suggestion of turning up naked to my customer tomorrow morning, I'm blaming you Linker3000. –  Kez Jan 25 '11 at 22:42
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A leather thong would be acceptable, but not a nylon one –  Linker3000 Jan 26 '11 at 7:04
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protected by studiohack Feb 15 '11 at 6:41

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