Okay, so how important is having a metal case now really for a PC?

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Elledan

[H]ard|DCer of the Month - April 2010
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Like the title says, what is the importance of a metal case (faraday cage, EMI) to a computer system? Granted, a PSU needs a metal casing due to the extreme EMI it produces (very noisy circuit), but for the other components?

With so many people putting entire systems in wooden, plexiglas and other non-conductive (shielding) cases, or even without anything resembling a case, apparently without any issues, what is the value in having the system encased in metal? This even ignoring the huge gaps at the front, back and other spots in those metal cases.

I've done some research, but I can't find any material which seems to give any clues. Seeing how many other consumer electronics are put in plastic cases, EMI shielding doesn't seem to be a high-priority anyway.

Any insights are welcome.
 
It's not all that important, really. If the computer is located near equipment that generates a lot of EMI, like motors, MRI, heavy-duty electrical equipment, etc, then it can make a difference.

It's important to remember that even inside a metal case, there's a lot of RF noise generated by the computer itself. You have hundreds of traces running across the motherboard, and each of them needs to be able to tolerate noise from its neighbors. The PSU, being switchmode, also puts out a lot of EMI, though most of that is trapped by the PSU's casing. In other words, the components are generally designed to tolerate the extra noise.
 
So in other words, the metal casing serves to protect the PC from outside interference, if it is present. I wonder what'd happen if you were to put a PDA, mobile phone or such next to a big EMI source...

One thing I have also wondered about is whether a single sheet of aluminium foil would be sufficient as well to block out the EMI. The math behind it appeared to be rather impressive when I last looked at it, though... perhaps I should give it another try.

Thanks, Mohonri :)
 
Are you worried about your computer reading your thoughts? Easier to make a tinfoil hat than a tinfoil case for your computer... ;)

Seriously, though, all electronics are "supposed" to be able to accept harmful interference without adverse affects.
 
i know what happens when i put my phone near my comp and wireless router. phone signal dies ;). that may have more to do with the router, though ;)
 
Logan321 said:
Are you worried about your computer reading your thoughts? Easier to make a tinfoil hat than a tinfoil case for your computer... ;)
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Nah :p

Just planning a new case without having the money and tools for going 'full-metal' :) I did want to do a sanity check beforehand, though.

Seriously, though, all electronics are "supposed" to be able to accept harmful interference without adverse affects.
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Sure, but an EMP will still kill most hardware ;)
 
Unless you completely isolate it from the outside world inside a Faraday cage or so ;)
 
I doubt you'll ever run into any interference, instability, etc. from having a non-conductive case. People have been using acrylic cases, "woodies", etc. for years.

Hell, running a metal-cased computer with the cover off probably radiates more than a omnidirectional-radiating unshielded case.
 
oh no I better switch to a different psu because it has a 120mm fan hole facing the cpu and an 80mm facing the rear!!@#!@# Need more tinfoil.
 
We don't need no stinkin' metal boxes ;)

colossus1fh1.jpg
 
That open PSU still scares the <censored> out of me :p

Love the cables, though.
 
Metal cases are only required under FCC "B" rules (business). For home use you aren't legally required, but manufacturers don't want to make two different cases. And steel offers strength at low cost which keeps down breakage and reduces safety related lawsuits. The metal case on a PSU is there to keep you from electrocuting yourself - I've run plenty of PSUs without cases and have had no problems. Aluminum won't help with EMI - it's magnetic! Aluminum isn't magnetized so there is no effect. It will help sheild RFI, but that's a different animal.
 
I see, that does indeed make sense :)

And that's a good point about aluminium as well. Steel cases do offer a benefit over them after all it seems, despite the hefty weight ;)
 
Fenris_Ulf said:
Metal cases are only required under FCC "B" rules (business). For home use you aren't legally required, but manufacturers don't want to make two different cases. And steel offers strength at low cost which keeps down breakage and reduces safety related lawsuits. The metal case on a PSU is there to keep you from electrocuting yourself - I've run plenty of PSUs without cases and have had no problems. Aluminum won't help with EMI - it's magnetic! Aluminum isn't magnetized so there is no effect. It will help sheild RFI, but that's a different animal.
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last time i checked Radio is an electromagnetic wave >.>
 
Fenris_Ulf said:
Metal cases are only required under FCC "B" rules (business). For home use you aren't legally required, but manufacturers don't want to make two different cases. And steel offers strength at low cost which keeps down breakage and reduces safety related lawsuits. The metal case on a PSU is there to keep you from electrocuting yourself - I've run plenty of PSUs without cases and have had no problems. Aluminum won't help with EMI - it's magnetic! Aluminum isn't magnetized so there is no effect. It will help sheild RFI, but that's a different animal.
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EMI = RFI.

Aluminum isn't magnetic, so it won't block a straight magnetic field by itself - you'll be able to stick two magnets together through an aluminum sheet. But an actual radiated EM field is a coupled electric and magnetic field, and if you block one you block one you block both. Aluminum effectively "shorts out" the electric component, blocking EM.

The company I work for builds hundreds-of-KW AM/FM radio transmitters with aluminum enclosures, and big matching coils and things inside which can create huge EM fields. We have no problem meeting radiated emissions tests.
 
Elledan said:
So in other words, the metal casing serves to protect the PC from outside interference, if it is present. I wonder what'd happen if you were to put a PDA, mobile phone or such next to a big EMI source...
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#1 The metal casing helps you carry around the parts, makes it less susceptible to breakage, and prevents coffee from being spilled on your PC.;)

#2 Have you ever put a cell phone next to an unshielded speaker? It's creepy in the middle of the night and you don't know how or why the speaker is beeping at you with the PC off. :D
 
tmclaugh said:
#1 The metal casing helps you carry around the parts, makes it less susceptible to breakage, and prevents coffee from being spilled on your PC.;)
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Well yeah, obviously :p

#2 Have you ever put a cell phone next to an unshielded speaker? It's creepy in the middle of the night and you don't know how or why the speaker is beeping at you with the PC off. :D
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Worse, I can identify the data the phone is communicating with the tower and know when I'm being called seconds before the phone starts ringing :D
 
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