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I have seen some projects building PCs in wooden case. I wonder how well this works with respect to grounding and EMI. A grounded metal case should work as a faraday case, and thus isolate the computer from the surroundings.

Notice that the EMI problems are not only related to the stability of the computer, but also the function of other devices, in particular radio receivers operating at microwave frequencies (WiFi, GSM phones, etc). After all, the PCIe bus may be thought of as a microwave antenna.

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    Grounding is not necessary for a Faraday cage. It helps to dissipate large currents, but you won't have those with a PC. – MSalters Oct 27 '17 at 9:53
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    They work just fine in an aquarium filled with oil or simply mounted directly onto a breadboard – Valorum Oct 27 '17 at 10:29
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    Most PCs these days are plastic laptops. – el.pescado Oct 27 '17 at 11:32
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    Most "plastic laptops" manage that by having smaller shields over the high-speed components on the motherboard. So the answer may well be, "It depends on your mainboard's construction." – Toby Speight Oct 27 '17 at 13:49
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    @el.pescad ALL of the laptops I've seen have conductive paint on the inside. Yes, the conductive paint is not very conductive, but it's enough for EMI purposes. The layers can be as thin as 0.025 mm and still work. That's why you'll often see that the insides of the laptops are yellowish or dark orange. – AndrejaKo Oct 27 '17 at 19:13
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A computer case does not need to be made of metal. The reason most cases are metal is because they conduct heat (helps disposing of internal heat a bit better if there are few fans inside), and more importantly, its cheaper to produce and the end product is less heavy. A computer case is not being used as ground, simply because the case itself does not touch the floor. They usually have rubber feet.

The case may be connected to the grounds of the motherboard, but that is not necessary, and it is mostly done in case the computer is not connected to a grounded wall-outlet.

That said, I've seen many people build computers from various materials, wood included but not limited to. Test pc's often have no case at all, but the best example is the desk pc, a pc build directly into a desk. These desk pc's are often made of wood.

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    @nfs it is not the case in the US either. Unless you live in an extremely old house, all wall sockets are grounded. – Moshe Katz Oct 27 '17 at 12:47
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    It also gets the computer as a whole through EMC testing, thanks to the shielding a metal case provides. This is to limit the chances of accidentally microwaving the user or similar health issues and to prevent it messing with your Wi-Fi, Cell phone, TV, Radio, etc. Wood does not provide much radio shielding so although the PC might be fine, you may cook. In practise a single device of only ~200W power is not going to do that much damage. A while house full of the might be another matter. – TafT Oct 27 '17 at 13:36
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    I would go so far as to say this answer is wholly wrong. FCC part 15 compliance isn't some sort of joke. It has a very distinct purpose and running around ignoring it is a really good way to get untraceable errors. – Sam Oct 27 '17 at 14:50
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    @MartinBeckett, Thank you for the astoundingly obvious but wildly useless statement, are you per chance a manager? %95 of the population might be able to ignore the FCC, not %95 of its computer users, or manufacturers. Of those that can ignore the FCC most have a very similar regulator and requirements. – Sam Oct 27 '17 at 15:25
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    "A computer case is not being used as ground, simply because the case itself does not touch the floor" -- what? I don't think most floors in residential or office buildings are conductive, so electrical grounding doesn't have much to do with touching the floor, right? – ilkkachu Oct 27 '17 at 16:26
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To pass the requirements of FCC part 15 class b most computers must be in some sort of conductive case. You will notice that most metal cases don't have any slots or holes larger than about half a centimeter, this has to to with antenna theory.

If you are building the projects for yourself, you do not have to comply to FCC part 15, but if you intend to sell them that is a different story. If you want to build a case out of wood and sell the resultant product (not as a kit, there is a whole weird legal thing about kits) you will almost certainly have to coat the inside with some sort of conductor.

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    I've seen more than one case design where one side wall is a thin meta frame around a large pane of see-through plastic. How does that mesh with "don't have any slots or holes larger than about half a centimeter"? – Reinstate Monica Oct 27 '17 at 15:19
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    @angew, honestly I don't know. Most of those are stand alone cases and wouldn't need to comply. In the case of manufacturers (falcon, ibuypower) I suspect one of two things. Either they somehow sell it as a "kit", or they use glass that is coated in something like PEDOT or similar compounds. – Sam Oct 27 '17 at 15:41
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    This would be much better if you outlined the requirements. At least, what kind of requirements are they? – Rolazaro Azeveires Oct 27 '17 at 20:29
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    My understanding is that even if the computer is for your own personal use, it can't interfere with other people's communications. If it caused problems for your neighbors and they complained, the FCC could still require that you mitigate the problem. – fixer1234 Oct 28 '17 at 7:51
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    @Angew isn't that plastic usually coated though? Without ANY foreknowledge, i would assume that it might be a metallic coating. – user801232 Oct 28 '17 at 19:28
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I've been through the guts of hundreds of computers, both desktops and laptops, and have re/built a number of them, often working on them with only a frame or even no case at all-- just parts on a bench. I've never seen any difference. I also play electric guitar, sensitive to radio and electronic interference, and can attest a pc case makes no difference.

My favorite mini-server I built for low power-consumption from the guts of an old HP g-series laptop, bolted to a sheet of plexi-glass. All the foil shielding makes no difference. It's run for years without any errors caused by electronic interference, transmitters, cosmic rays, or solar flares-- though that last bit did measurably affect wifi communications between other devices and the AP's, but those were on another network segment and physically seperated by a router and 5 to 100 feet of space, so obvi would not have been in the case anyway.

I actually tested this with various transmitters and power-supplies brought in close proximity. No perceptable difference, and nothing in the error logs to suggest it was affected. A guitar pickup likewise is affected the same by PC's with or without a case. Kind of a cool, practical test for outgoing interference as you can actually hear it. Also necessary if your a guitar player. Grounding the PC also seems to make no difference to the PC in terms of function, though possibly in terms of safety in extreme cases, but you don't need a box for that.

If it is a concern, and you like wood cases, you can always line it with foil, or foil tape. A sheet of Reynold's behind your AP rounded a bit like a dish works wonders for reflecting or focusing your wifi signal, just like the reflector in a mini-maglite. You can test it with a wifi analyzer app on your phone, so it will definitely do a lot to keep interference in or out of your box. But like I said, I have tested it and see no practical difference.

For an easy real example of interference, try having a conversation, listening to Pandora, downloading something etc. on your cell-phone within 3 to 5 feet of your average microwave oven. If it's not one of those cheap dinky one's, you will notice significant chop, or even total signal jamming. If that's considered safe, I think I'm ok without a metal box. My naked server sat on a shelf on my desk less than two feet from my skull. I've never noticed any difference there either. More worried about my laptop in my, well, lap.

Now... where did I put my tinfoil hat? ;)

  • You can only "hear" up to ~20,000Hz if none of the harmonics of a 3GHz processor make it down there at any appreciable amplitude I would not be surprised at all. There is a reason FCC compliance testing costs tens of thousands of dollars at minimum. How would you feel if you had a pacemaker and your neighbor's computer interfered with it because "they tested it with a guitar" (besides dead)? – Sam Nov 21 '17 at 18:47
  • Well, I would haunt the marketeers who sold me a bunk pacemaker and didn't tell me I needed to stay away from all other technological devices. The fact is we are surrounded every day by all sorts of EMF interference, both 'natural' and man-made-- and some quite loud. Actually, I can hear <40k due to birth defects in my ears, according to military testing. Thank God for flatscreens! A lot of CRT's I can hear screaming from across the street! I know how to use tools. But how do you think things like SWR meters came about? Try the microwave thing if you don't have a guitar. – jdmayfield Dec 9 '17 at 10:38
  • Oh, yeah.. trust me they do. As an IT guy, sound is one of my first tools to guide my steps toward a diagnosis if there may be a hardware problem. And smell, of course. Anyway, just about any decent amp will do the trick. You can literally hear programs running. I didn't make this up. There's some great vids on Youtube about using home-brew coils (and pickups!) to sniff electronic activity. Computar parts, fans, cell-phones, even your watch! If it's leaking EMF in the audible range, almost certain other bands will leak as well. The foil thing does work. A hat's a bit much though. – jdmayfield Dec 9 '17 at 10:55
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I don't imagine you were thinking about Raspberry Pis (or other SBCs), but I'd estimate that 80% of all Raspberry Pis ever sold are either in plastic cases, the cardboard box it was posted in, or in no case at all.

A metal case isn't a hard-requirement, although can offer some benefits if you want to do some EMI shielding. You can do the same shielding with some metal that's not integral to the case though, if you need want the shielding without the case.

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Faraday shielding is not necessary in most circumstances. My primary computer is in a wooden case, and it works. If you were building a machine meant to be really high-reliability, perhaps a metal case would save you from occasional cosmic rays.

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    Isn't tinfoil the material of choice when protecting from cosmic rays? :) Sorry for the joke, but I don't think a metal case makes much of a difference. Do you have a citation to back up your claim? – Ajasja Oct 27 '17 at 9:47
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    The shielding is not there to make your PC work, but to make other devices work near your PC. – MSalters Oct 27 '17 at 9:54
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    Like MSalters says, it's not your PC that needs it, but everything near it. The interference can affect anything from radios and TV to electric guitars or other audio equipment. The interference can manifest as clicks or other sounds, visual artefacts, etc. Or simply produce signal noise in radio traffic (think WLANs, phones, etc), worsening the connection quality. – DocWeird Oct 27 '17 at 13:00
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    @DocWeird wouldn't PC cases with windows also fail at defeating interference? – Ave Oct 27 '17 at 15:18
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    The PC cases with windows do indeed tend to fail emissions (And sometimes susceptibility) when you build up a machine and put it in a test chamber (Been there, done that). Most of that stuff is however sold as an empty case to the gamer market who then build up the machine in it, as such the case is the thing brought to market, not the complete machine. I suspect the shops selling PCs in such cases fly under the radar to a large extent. – Dan Mills Oct 27 '17 at 15:57

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