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Electrical Grounding in ATX Cases?

Posted by Cliff on from the breaking-out-of-the-beige-box dept.

FoxMulder asks: "I'm constructing a clear case made of Plexiglas for my new athlon machine. I don't know for sure how the grounding system on ATX power supplies work, but I am wondering what I can do to properly ground my machine without the use of the metal case that is so classicly accepted. I also am interested to find out which parts of the machine should be grounded, and to what. I've had a little bit of an electric bill problem when my last computer with an AT power supply wasn't grounded properly."

3 of 30 comments (clear)

  1. RFI by Xenu · · Score: 3

    Without a metal case, you should also think about the RFI (radio frequency interference) that will be generated by the computer. You need some sort of electrically conductive coating on the plexiglas. See the previous slashdot discussion, How to Build a Clear Computer Case.

  2. Re:Yes and no - RFI abatement how-to. by Xenu · · Score: 3
    Here are some hints from looking at TEMPEST qualified (NSA approved) computer equipment:
    • Copper braid or finger stock on seams where covers are attached.
    • Lots of screws to make sure that pressure is applied to every part of a seam.
    • Connectors for external cables have built-in bypass capacitors.
    • All external cables are shielded.
    • Metal mesh over fan exhaust port.
    • No holes in case larger than, I forget, 1/4 or 1/2 wave, at the highest frequency that you are concerned with.
    • All chassis parts have good electrical connections to each other.
    • AC power input goes through a good line filter.
    • Special conductive coating used on front of CRT.
    • Metal covers over floppy drives and other drives with holes for loading media.

    The two big things are to eliminate or reduce the size of holes and to prevent RFI from getting out via the external cables and AC cord.

  3. Grounding/Power Issues by Matt_Bennett · · Score: 3

    Grounding should not be a problem- Ideally, you should never use the case of a computer as a current return, it should all be done with the wires back and forth from the power supply. Most metal cases are grounded for a number of reasons- if a live AC wire were to touch it, you want the circuit breaker/fuse to blow so you don't create a safety hazard, plus if it was insulated from everything else, it could attract a static charge. It is also grounded to reduce the radiated emissions from the computer, but it would serve that purpose even if it wasn't grounded, since there is probably enough capacitance to ground at the frequencies of interest anyway. If you want shielding find some copper mesh (like window screen, but copper) and line the inside of the case with it- as long as the openings in the mesh are small, it will serve just as well as a RFI shield.

    With a truly transparent case, it would be hard, but not impossible to make a shielded case- but you can put conductors on glass- every LCD display has conductors on a transparent surface. For for a while had a (front) windshield defogger that was one solid conductor- radar detectors couldn't see through it, but you shure could.

    As to power problems? I'm guessing that this chap had his ground where the neutral ought to have been. Electric utilities frown upon drawing unequal currents from the two legs of your power, and charge a surcharge when that happens, similar to if you have a strongly reactive load- The heaters in large foundries are highly inductive, to correct the power factor, they have huge capacitor rooms to put the current and voltage back into phase. On the other hand, I can't see why a load as (relatively) small as a computer could cause this sort of surcharge.