5

Is it safe to connect yourself to an electrical outlet?

Either directly or indirectly.

I would prefer to not connect myself directly to an electrical outlet, via (as I've heard) attaching a wrist strap to the middle screw of an outlet.

Though I am wondering about connecting more indirectly.

I am building a computer, that has a fully painted case. I have heard of a way to ground using the computer's power supply by:

Plug in power supply to wall outlet, turn power supply OFF, partially unscrew one of the four power supply screws (that hold it onto the computer case), then attach the anti-static wrist strap to the threads of the unscrewed screw.

Is that safe, in regards to indirectly connecting yourself to a wall outlet?

I would prefer a standalone ESD setup, that doesn't involve a wall outlet, however I have not yet heard of any ways to do so.

Thank you very much for helping with this.

Smiith
  • 89
  • 1
  • 1
  • 5
  • Sounds like an application form for a Darwin award is on the way - avoid connecting yourself to a power outlet. – JIm Dearden Feb 26 '17 at 17:11
  • 3
    If the wall outlet is switched, the earth connection will still be connected when the outlet is switched off. – Andrew Morton Feb 26 '17 at 17:47
  • The title is way more interesting than the question... – dalearn Feb 26 '17 at 22:02
  • The round center pin of a US 3-prong AC outlet *should* be reliably grounded. I would tend to trust it in professionally wired homes and businesses, especially if subjected to inspection by (honest) electrical inspectors. I would be less inclined to trust it if the outlet was wired by the homeowner. (In theory you can even ground to the wide prong of a 2-prong outlet, but this is iffier, for several reasons.) – Hot Licks Feb 27 '17 at 02:43
  • so you are leaving the computer powered while you work on it (in order to have this ground be useful). If you are doing this much work on this computer then perhaps somewhere inside use an internal chassis screw and make a permanent grounding strap connection. – old_timer Feb 27 '17 at 16:05
  • You only need to connect yourself to Earth, and then leave the power supply plugged in (but switched off in as many ways as possible - ideally at the wall socket). Earth is not switched, and so will keep the PC, case, PSU and other things at Earth. That said, when we had our house rewired, they did all the work, let us move in and then a couple of months later when they were 'filling in the paperwork' realised that we had never had a proper Earth connection (no idea what our predecessors of 20 years were doing!). Putting one in took them about an hour though, I seem to remember. – Ralph Bolton Feb 27 '17 at 16:16
  • Would it work to just connect myself and anything I'm working with to the computer case, without plugging it into the wall outlet via psu? Thank you very much. – Smiith Feb 28 '17 at 04:54
  • The PC's PSU must have a power switch and you must switch off the PSU. Then, yes, you can connect your wrist strap to your PC (1MΩ resistor in the coil cord) and leave the power cable plugged into the wall outlet. But, [i have learned you should not rely on the power switch](http://electronics.stackexchange.com/a/295742/127725). Although it's probably going to be fine, you should disconnect the power cable to be 100% sure, instead of 99%. You can make your own ground wire between the PC and mains earth. –  Apr 09 '17 at 16:09

4 Answers4

21

If your plug has a correctly wired earth pin, then you can use that to ground yourself.

However before you do, it is worth noting that all reputable ESD wrist bands contain an embedded 1MOhm resistor. This is done primarily so that if you accidentally connect yourself to mains voltage (either through what you are handling, or through a wiring fault in the plug) the resistor limits the current that can pass through you, and so protects you from certain death.

I would suggest buying an ESD wrist strap. If you make your own, be sure to include a 1M resistor.

To be fair though even if you don't include the resistor, as long as you are absolutely sure you have connected yourself to the earth pin and nothing else, it will not do anything worse than touching the back panel on your PC (or the case of the PSU) because those are generally tied directly to earth on the outlet anyway. If touching your PC gives you an electric shock, consult an electrician.

As an alternative to the earth pin on an electrical outlet, you can also use things like metal plumbing pipes as these are typically earth bonded to the electrical system earth in the house, or go down physically into the ground.

Tom Carpenter
  • 63,168
  • 3
  • 139
  • 196
  • 3
    I would add : if your plug has an earth pin AND the house wiring passed its correct connection and earth continuity tests... –  Feb 26 '17 at 17:25
  • 1
    My understanding is that the purpose of the resistor is to force current to equalize slowly, to prevent component-damaging static discharge. It's a functional requirement of the strap, not just a safety feature. – BlueRaja - Danny Pflughoeft Feb 26 '17 at 20:44
  • @BlueRaja-DannyPflughoeft Nope. There's a lot of misconception about how ESD wristbands work and the point of the 1Mohm resistors. See [this Q&A](http://electronics.stackexchange.com/a/274846/53368) – Tom Carpenter Feb 26 '17 at 20:55
  • That is very informative. Would just connecting my wrist strap to the computer case while it is plugged in (but power supply turned off) provide the same ESD grounding as if I were to attach my wrist strap to the ground outlet on a wall socket? Thank you very much. – Smiith Feb 27 '17 at 01:47
  • @Smiith -- the short answer is "yes, as long as the case has proper continuity to the earthing pin" – ThreePhaseEel Feb 27 '17 at 02:38
  • Connecting yourself to ground is dangerous. Should you touch any high voltage, one becomes a candidate path of least resistance. The 1M resister is also to insure the person is not the easy path to ground. – chux - Reinstate Monica Feb 27 '17 at 04:58
  • Actually, if your intent is to simply protect from touching components inside the computer case, then connecting the strap to the case works fine, even if the case itself is not somehow grounded. The hazard, if the case is not grounded, but you are "grounded" to the case, is that you might reach over to pick up a SIMM off your workbench and zap it. Everything you touch needs a common ground to be "safe". – Hot Licks Feb 27 '17 at 12:44
  • Could I attach everything to the case to make a common ground? Thank you – Smiith Feb 27 '17 at 21:19
  • @Smiith if your case is grounded through the power supply, yes. You will need to leave the computer plugged in to ensure it is grounded, but you can turn the power off either at the wall or PSU if it has its own switch. – Tom Carpenter Feb 27 '17 at 22:47
  • Would it also work if the computer wasn't plugged into the wall? Thank you very much for all this information. – Smiith Feb 28 '17 at 00:39
  • @Smiith if it isn't plugged in, it's not earthed. – Tom Carpenter Feb 28 '17 at 06:41
5

You can get plugs specifically for the task, although the expense is probably not warranted for a one-off use:

enter image description here

The live and neutral pins on the plug are plastic. The one illustrated conveniently has press-stud, screw terminal, and 4 mm banana sockets.

It is OK to attach an anti-static wrist band which already has a 1 MΩ resistor.

Andrew Morton
  • 2,389
  • 1
  • 17
  • 26
  • To be doubly sure, you could plug in a passive outlet tester first to make sure the safety ground isn't somehow hot. – Todd Wilcox Feb 26 '17 at 20:20
  • 1
    @ToddWilcox -- I'd actually check the receptacle strap with a non-contact voltage detector *instead* of using a 3-light "passive" outlet tester (one of the most common ways to get a live earth connection on a receptacle *can't be caught by a 3-light tester* -- look up "reverse polarity bootleg ground" for more info) – ThreePhaseEel Feb 26 '17 at 21:28
  • Thank you for that info. Those ESD plugs do look like a nice option to have. Are they what gets typically used for full ESD setups? – Smiith Feb 27 '17 at 01:49
  • @Smiith I wouldn't know: I only got one because it was convenient for me to use. – Andrew Morton Feb 27 '17 at 19:54
-1

Never connect yourself to power outlet. ESD connectors should be indeed grounded. There are also special band that you put on your hand to ground yourself and discharge your body from electrical charge and avoid ESD that way.

But remember - when you are grounded - especially to power neutral you are highly exposed to electrical shock. If you touch any live power cable (with phase) you are dead. And when you ground yourself to power outlet's neutral wire then even security systems in your house installation (like residual-current device) won't help.

zupazt3
  • 1,567
  • 4
  • 17
  • 27
  • 3
    He's not talking about grounding himself to the neutral slot, he's talking about using the middle screw of the outlet, which is typically connected to the ground pin. You say _"ESD connectors should be indeed grounded"_, but you don't say how it should be grounded if not to the electrical grounding system. Few homes have a dedicated ground system that might be found in an industrial setting. The ground pin of the outlet is connected to the chassis of my computer, so I clip the ESD lead to a bare metal tab on the back of my computer. – Johnny Feb 26 '17 at 21:14
  • 1
    But neutral pin is very often connected to middle screw of the outlet (like in TN-C networks). What I wanted to point out is that connecting yourself to a ground greatly increase danger of shock. – zupazt3 Feb 26 '17 at 21:46
  • 2
    @zupazt3 -- where on Earth are you that you have TN-C inside a building? – ThreePhaseEel Feb 26 '17 at 22:03
  • That is very good to know. Thank you very much for that information. – Smiith Feb 27 '17 at 01:49
  • 1
    @zupazt3: I have never ever seen the middle screw of an outlet to be connected to anything but GND, if anything at all. Safety code would forbid that here. Given that and that you seem to have tnc in buildings it would be interesting where you are from to be aware of the dangers of that countries electrical installations. – PlasmaHH Feb 27 '17 at 07:53
-1

YES! The ground wire in the outlet is security feature by design. To fulfill ESD specification, everything, including you, shall be on the same, grounded, potential by design.

If you connect yourself to a ground wire, it should be safe.

If you connect yourself to a neutral wire, it should be safe.

If you connect yourself to a hot wire it depends how you are connected, what your health status is and how lucky you are...

If you touch the wire while on floating potential, ie. not connected to anything else, it is safe. If you are grounded, you can get a kick, suffer form burns or die (from burns or hearth attack). Kids, do not try it at home.

Anecdotally; Resistance of five people is high enough that when they hold each other's hand one can hold the ground wire and fifth can touch the hot wire. They all get small shock. The number of five was found out during experiments on students during physics course. :) Professor was the one, who touches the hot wire.

Regarding the questions burried inside the text:

The case is here just to hold all the parts in the position. You can build wooden case, glass case, whatever you want. If the case is conductive it must be connected to the ground wire of the outlet. As any other electrical device. When you get kicked when touching the case there is something terribly wrong with the outlet or the wiring in the house.

If the device has no ground wire, in must be sealed so you cannot reach working parts at all.

If you don't have proper qualification you should't be able to touch hot wire/part at all. Unless there is malfunction (insulation got broken) or you are darwin prize nominee (you are fool enough to open the device and play around with the wires inside).

Regarding the computer design: Everything inside should have the common ground (usually the case). If you want to have insulating case, you should connect the components to different common ground - thick copper wire. If the case is conductive it is "the stuff thet holds it together" and common ground simultaneously.

Regarding your plan: The power supply case (the box with female screws) is already grounded via outlet. Anytime you touch the screw in the washing machine, fridge etc, you get connected to the case which is grounded via the outlet.

As I looked for some ESD setups, the point of static discharge suppression is in keeping everything on same potential, the ground.

If you try to build ESD workplace without any connection to the outlet your cross-wiring the case, yourself, desktop, floor etc. will equalize the potential to the same voltage but uknown voltage to the ground. There would be a risk of lighting a discharge between any part of your ESD setup and the actual ground.

If you connect everything to a single ground wire in single outlet, you will get no potential difference betwee the connected parts (you, the case, desktop,...) and the ground. There is no risk of discharge at all.

If you want to be connected during working IN the computer, for gods' sake, plug it off the outlet first and don't be conected to anything at all.

Crowley
  • 389
  • 1
  • 2
  • 8