Does a PC have to be mounted in metal case

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.

case

user877329

Posted 2017-10-27T06:23:47.053

Reputation: 679

May be I am wrong or not understanding your question but what I understands is most probably the wooden cases give extra protection layer to user and PCs. For daily usage prospective view, wooden cases give protection to user from electric shocks and keep PC safe from physical damages. – The iOSDev – 2017-10-27T06:34:55.270

2Grounding is not necessary for a Faraday cage. It helps to dissipate large currents, but you won't have those with a PC. – MSalters – 2017-10-27T09:53:15.380

They work just fine in an aquarium filled with oil or simply mounted directly onto a breadboard

– Valorum – 2017-10-27T10:29:46.403

7Most PCs these days are plastic laptops. – el.pescado – 2017-10-27T11:32:24.773

18Most "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 – 2017-10-27T13:49:44.000

4@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 – 2017-10-27T19:13:28.170

All I know is that when I remove the side panel from my computer, an interaction starts up between my computer and my vtech digital phone. It creates a high pitched sound coming from the computer itself. Place my hand between the two, and it stops completely. My hand becomes a shield. – Sean – 2017-10-28T19:20:48.593

@Sean ... and may become hotter due to dissipation of the radiation in your hand. – user877329 – 2017-10-28T20:04:05.843

What gets me is that the phone is the source ( and the computer becomes the detector ), and it is so even though I have not picked up the phone to activate it. Is it safe? But of course my original point was that computers can also be sensitive to incoming signals rather than them possibly be sending dangerous signals outward, or interference signals outward. – Sean – 2017-10-29T20:24:33.387

@AndrejaKo you could paint wooden case with conductive paint, couldn't you? – el.pescado – 2017-10-30T06:55:38.363

@el.pescado Well, you'd have to take a look at the datasheet of the paint. The thickness of the paint layer would probably heavily depend on the surface finish of the wood, but in general, I'd say that it should be possible. – AndrejaKo – 2017-10-30T07:20:59.550

Answers

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.

LPChip

Posted 2017-10-27T06:23:47.053

Reputation: 42 190

2Or, you know, most laptops. They are not that different from a desktop PC. – ecc – 2017-10-27T12:09:04.963

4May I assume you live in the US? Quote: "because in most households, the place the pc is placed, there's no grounded wall-sockets." This is not the case in Germany, where pretty much all wall-sockets are grounded. (I suggest you clarify your post.) – AplusKminus – 2017-10-27T12:43:27.190

11@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 – 2017-10-27T12:47:53.863

Ok, I guess I have been misinformed. I'll edit that part out. – LPChip – 2017-10-27T12:49:04.197

9It 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 – 2017-10-27T13:36:10.000

8If you want to sell (commercially) an unshielded PC, you'll find it difficult to achieve the required emissions limits - and even for a home-built machine, you may find that you're liable if EMI causes problems to other people nearby. – Toby Speight – 2017-10-27T13:47:07.920

25I 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 – 2017-10-27T14:50:36.700

2@Sam fortunately 95% of the World's population can completely ignore the FCC – Martin Beckett – 2017-10-27T15:21:25.217

9@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 – 2017-10-27T15:25:30.533

@LPChip: all UK sockets are grounded.

– Steve Melnikoff – 2017-10-27T15:37:02.290

Is it really about heat conductivity? I always thought it is to ground the case. Now I am wondering what are the little metal prongs on motherboard's backpanel shielding good for.

– Vlastimil Ovčáčík – 2017-10-27T15:54:43.783

6@VlastimilOvčáčík The fingers make metallic contact between the IO shield and the surrounding metalwork to avoid creating a 'slot radiator' witch if excited by RF from the system at a frequency where it is resonant will cause an EMC fail. For a case to be an effective screen there must be metal to metal contact along all seams, and holes should be smaller then 1/10th wavelength at the highest frequency of interest, look at old SUN or HP workstations to see it done right. – Dan Mills – 2017-10-27T16:03:42.723

26"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 – 2017-10-27T16:26:55.583

1@Moshe Katz: That depends on your definition of "extremely old". My house was built in the 1960s, which I consider fairly recent. It didn't have grounded wall outlets when I bought it - though I've since updated most of them. – jamesqf – 2017-10-27T16:47:08.340

6@jamesqf The US has required grounded outlets since at least 1959. If your house built in the 1960s had two prong outlets, it was not built up to code. – Moshe Katz – 2017-10-27T16:57:44.173

@Moshe Katz: That may be so, but it's rather beside the point. I wouldn't think of a house built in 1959 (or indeed, 1929) as being extremely old. – jamesqf – 2017-10-28T03:11:22.133

2The metal in a case is not used to conduct heat in a computer. The motherboard is connected via small standoffs, there is very little means to conduct heat from the cooling to the case. A case helps in cooling by facilitating airflow, but the material choice matters little. – whatsisname – 2017-10-29T03:20:18.120

@whatsisname not necessarily. I didn't say metal is used because it needs to cool the interior, but if you compare the inside temperature of metal vs wood, then wood, who will retain heat inside will have a more significant effect, thus requires better airflow, than with metal. I guess I should say: its less likely that heat stays inside the case with metal than with other materials, such as wood. – LPChip – 2017-10-29T12:16:43.567

2@SteveMelnikoff No they are not. The two prong sockets in bathrooms for shavers are not grounded ;) – DavidPostill – 2017-10-29T13:07:33.357

1@Sam: 95% of the world's population. Martin is reminding you that, although you live in the USA, not everybody else does. – Lightness Races with Monica – 2017-10-29T18:47:31.573

@LightnessRacesinOrbit and I am reminding Martin not to be pedantic. – Sam – 2017-10-30T02:49:21.333

The case is grounded, but not because the case touches (or does not touch) the floor. In a typical computer the power supply is physically touching the metal case via four case screws, which has electrical conductivity to the ground wire in the power cable, which eventually connects to ground in the breaker panel. Yes, it is possible to avoid this by not using a metal case, or any case at all, but most computer cases are made of metal and work this way. – None – 2017-10-30T04:44:47.453

Love coming to the comments for the extended discussions. – RyanfaeScotland – 2017-10-30T10:58:17.250

@LPChip Your views on heat being trapped in a metal case are wholly wrong. There is little to no contact of the heat-sensitive components (CPU/GPU heatsinks, for instance, but also HDDs and PSU components) with the case of the computer. A heatsink, for instance, will conduct heat away from the processor die to its fins, and then the air moving across the surface of its fins pulls the heat away. This will work exactly the same in a box made of wood or a box made of metal, provided the airflows are the same. – Shamtam – 2017-10-30T12:11:45.487

The thermal resistance of the motherboard's PCB to the case (typically a couple contact points of the motherboard touching some standoffs) is extremely high compared to the actual heat-exchanging components. Using a wooden case would have no appreciable impact on heat transfer in a typical computer. – Shamtam – 2017-10-30T12:12:52.543

Also, your comments on grounding are also quite misleading. As others have stated, the rubber feet on a typical case have nothing to do with whether the case is grounded or not. I agree that the grounding of the case isn't necessary, but I can guarantee any typical PC will have a grounded chassis, as the PSU and the motherboard typically connect their electrical grounds to their mounting points. Regardless of whether or not the PSU is earth grounded at the socket, the chassis will very likely be grounded relative to the electronics in the computer. – Shamtam – 2017-10-30T12:16:13.850

The answer doesn't mention rubber feet wrt. the case being grounded (which is obviously is via the power supply) but wrt. the case being used as a ground (which it obviously isn't). – Useless – 2017-10-30T13:13:30.493

Grounded wall sockets have not been mandatory in new houses until mid-1990's in Finland. And they never became retroactively mandatory, so 90 % of the houses in Finland in general will only have grounded sockets in the toilet (and kitchen, but only for the fridge in practice). – Juha Untinen – 2017-10-30T13:46:52.077

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.

Sam

Posted 2017-10-27T06:23:47.053

Reputation: 597

11I'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"? – Angew is no longer proud of SO – 2017-10-27T15:19:08.067

3@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 – 2017-10-27T15:41:54.573

2This would be much better if you outlined the requirements. At least, what kind of requirements are they? – Rolazaro Azeveires – 2017-10-27T20:29:38.297

8My 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 – 2017-10-28T07:51:46.983

1@Angew isn't that plastic usually coated though? Without ANY foreknowledge, i would assume that it might be a metallic coating. – None – 2017-10-28T19:28:56.963

@fixer1234 Probably the standard is different - e.g. if you're making something for mass-production you have to test and certify it won't cause problems, while if it's a personal one-off you just have to promise to turn it off if it does cause problems, because the potential scope of problems is much lower if there's just one device out there. – user253751 – 2017-10-29T23:49:13.103

This answer would be better if it made direct reference to electromagnetic interference & other unwanted effects that FCC part 15 class b presumably concerns itself with. As has been pointed out above, "because of FCC rule..." is not a helpful reason for/against something for someone outside of the US (or making products for use there). – Joe Lee-Moyet – 2017-10-30T16:01:20.460

@yjo, you are correct, I could lecture people on EMI and the reasons you should care, but I tend to take a more Socratic approach with my answers. Is that appropriate for a place like stack exchange? I don't know but it's my approach. I want people to be curious and go read about FCC part 15 and similar regulations and understand them. Something I could not provide in an answer here. – Sam – 2017-10-30T16:15:21.503

@Sam you're missing the point that your answer is totally US-centric. A user in the UK or India reading your answer won't learn anything useful from your answer unless they're building a product for use in the USA and know that they'll need to comply with FCC regulations. – Joe Lee-Moyet – 2017-10-30T16:25:57.593

@yjo, No, people in India will have to conform to the equivalent regulations from TRAI and people in the UK will have to conform to Ofcom regulations. I would put a fair amount of money on the fact that every country that has a reasonable large electronics market has regulations similar to FCC part 15, and most likely modeled after the US's (technically correct regulations are hard to write and why replicate work). If you are honestly too dense to figure that out then there is a little down pointing arrow you can avail yourself of. – Sam – 2017-10-30T16:45:46.800

@sam My suggestion is that a form like "Yes, you should care about EMI; [here] are some problems that it can cause. You're likely to be subject to regulations controlling EMI, e.g. FCC part [...], especially if you're making products for sale." would be a better structure for your answer as it gets to the universal why that the OP seemed to be asking for without assuming a narrow context (US commercial products) that was never specified. – Joe Lee-Moyet – 2017-10-30T16:50:43.170

@yjo, I know exacly what your suggestion is. You have already given it to me. Hell, RolazaroAzeveires gave that same suggestion 2 days ago. I didn't take it because as I already explained in my earlier response I expect people to be curious and to be able to logically apply things to their own lives. If you look at the bottom of this page there is a "Add Another Answer" button, you should use it. – Sam – 2017-10-30T17:00:05.133

This is not actually true, FCC 15b list the maximum acceptable emissions for a device, but it does not REQUIRE a grounded metal case. While a grounded metal case is an easy way to mitigate emissions, and is also used as a means to pass FCC, lower power electronics, and even some computers (Raspberry PI) already pass FCC with no enclosure. – KJ4IPS – 2017-11-21T18:27:11.297

@KJ4IPS, that is why I said "most computers". Also to my knowledge the Raspberry Pi is sold as a development kit and is not tested to FCC part 15b – Sam – 2017-11-21T18:30:41.637

@Sam, For what it matters, the rPI has both CE and FCC. I don't have a link to the CE filings, but here are the FCC ones. https://fccid.io/2ABCB-RPI32. At a previous employer, we were considering embedding it into a product.

– KJ4IPS – 2017-11-21T18:38:54.030

@KJ4IPS the 2 and 3 pass fcc https://www.raspberrypi.org/documentation/hardware/raspberrypi/conformity.md not the w or 1

– Sam – 2017-11-21T18:41:57.313

@Sam Yes, the foundation did not perform testing on the first generation (testing is expensive,) but the W actually has (https://fccid.io/2ABCB-RPI0W), I assume the page has not yet been updated.

– KJ4IPS – 2017-11-21T18:54:48.920

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? ;)

jdmayfield

Posted 2017-10-27T06:23:47.053

Reputation: 119

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 – 2017-11-21T18:47:48.097

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 – 2017-12-09T10:38:37.307

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 – 2017-12-09T10:55:18.233

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.

Ralph Bolton

Posted 2017-10-27T06:23:47.053

Reputation: 119

-2

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.

Aaron Brick

Posted 2017-10-27T06:23:47.053

Reputation: 182

8Isn'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 – 2017-10-27T09:47:27.980

28The shielding is not there to make your PC work, but to make other devices work near your PC. – MSalters – 2017-10-27T09:54:13.190

6Like 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 – 2017-10-27T13:00:06.773

2@DocWeird wouldn't PC cases with windows also fail at defeating interference? – Ave – 2017-10-27T15:18:04.260

6The 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 – 2017-10-27T15:57:39.287

1@Avery "... PC ... with windows also fail ...?" With a capital W, this is an interesting question. – chux - Reinstate Monica – 2017-10-27T21:05:05.930