Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.arch > #3566

Re: Alternatives for ground (for PC's)

Cross-posted to 5 groups.

Show all headers | View raw

In article <pjflj8-soh.ln1@radagast.org>,
Dave Platt <dplatt@radagast.org> wrote:
>In article <372b9$4e67eabc$5419acc3$27428@cache6.tilbu1.nb.home.nl>,
>Skybuck Flying <Windows7IsOK@DreamPC2006.com> wrote:
>
>>It does raise the interesting question, why PC's need ground and everything 
>>else does not.
>
>Your assumption ("everything else does not") is false.
>

There are at least three types of ground. The first one, referred to
by mr Platt, is the safety ground. This is designed to deflect chassis
currents; keeping the voltage people, animals etc are exposed to to
levels where less than 30mA is carried through the person/animal.

At low levels of leak this takes care of itself, the ground has
so much less resistance than the alternate path, so the exposed voltage
is very low. If the leak increases, wires or fuses will break. 

For the intermediate case ground fault breakers have been installed. This
is a more recent development. Fuses date to the 1880s, invented 4 hours after
Edison discovered (or invented, as he claimed) the short circuit.

Then there is shielding ground. The purpose of this is to make an electromagnetic
inert shield around signal carrying wires, to dampen interference and
signal leakage. This can be carried to extremes, like in tempest enclosures.

And at last there is signal ground. This is one part of a circuit carrying a
signal. In some cases signal and shield is the same, e.g. RG58 carrying 10base2
signals. This has a lot of disadvantages, if there are shield problems you may
get creeping currents all around your network.

It is a good idea to separate all of these. You normally want a safety
ground capable of carrying at least 3 times the current of the heftiest 
connection, to be sure it will make a short and blow a fuse when there is
a leak.

Modern signals do away with signal ground, and go for differential signals, 
since these are far less exposed to leakage, deterioration etc.

-- mrr Who once worked for KPN. They have a grounding fetish.

Back to comp.arch | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Alternatives for ground (for PC's) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-07 23:33 +0200
  Re: Alternatives for ground (for PC's) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-07 23:34 +0200
    Re: Alternatives for ground (for PC's) Mark Thorson <nospam@sonic.net> - 2011-09-07 14:57 -0800
      Re: Alternatives for ground (for PC's) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-08 00:05 +0200
        Re: Alternatives for ground (for PC's) dplatt@radagast.org (Dave Platt) - 2011-09-07 17:42 -0700
          Re: Alternatives for ground (for PC's) Robert Wessel <robertwessel2@yahoo.com> - 2011-09-07 20:15 -0500
          Re: Alternatives for ground (for PC's) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-08 05:33 +0200
            Re: Alternatives for ground (for PC's) Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2011-09-07 22:20 -0600
            Re: Alternatives for ground (for PC's) dplatt@radagast.org (Dave Platt) - 2011-09-07 22:32 -0700
              Re: Alternatives for ground (for PC's) BGB <cr88192@hotmail.com> - 2011-09-08 01:15 -0700
              Re: Alternatives for ground (for PC's) "Nobody > (Revisited)" <usenetharvested@aol.com> - 2011-09-08 01:17 -0700
                Re: Alternatives for ground (for PC's) dplatt@radagast.org (Dave Platt) - 2011-09-08 11:05 -0700
            Re: Alternatives for ground (for PC's) Martin Brown <|||newspam|||@nezumi.demon.co.uk> - 2011-09-08 08:13 +0100
            Re: Alternatives for ground (for PC's) Jasen Betts <jasen@xnet.co.nz> - 2011-09-08 12:55 +0000
          Re: Alternatives for ground (for PC's) Morten Reistad <first@last.name> - 2011-09-08 13:18 +0200
      Re: Alternatives for ground (for PC's) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-08 00:07 +0200
  Re: Alternatives for ground (for PC's) Quadibloc <jsavard@ecn.ab.ca> - 2011-09-09 18:01 -0700
    Re: Alternatives for ground (for PC's) "Skybuck Flying" <Windows7IsOK@DreamPC2006.com> - 2011-09-10 03:55 +0200

csiph-web