On Fri, 20 Oct 2006 08:04:56 -0400, John Gilmer wrote:

"RBM" rbm2(remove wrote in message
...
Things like computers "need" to be grounded

Not at all.

They work just fine, thank you, with a "floating" ground. Often, however,
where these is a ground provided there is a network which provides a small
leakage path between BOTH power conductors and the chassis (ground). The
effect of this network would be to cause the chassis get a voltage on the
order of 55 volts. There is no shock hazard and the leakage of even
several of these systems is not likely to trip a GFCI.

There is a lot of "tradition" here.

When IBM started making PCs they had a ground. When folks starting making
audio/visual stuff include stereos and TVs, there usually wasn't a ground.
But both classes of equipment have user exposure to the "chassis." In the
audio/visual stuff its from the "RCA" female connectors. In the PC world
it's the connector shell including the mouse, keyboard, USB stuff, printer
and serial interface.

There's a big difference between A/V equipment and computers. Well, at
least in Europe, I don't know much about US regulations.
Most A/V stuff has reinforced or double insulation. That's why they
have a plug without ground. Computers (except some laptops) usually
have only 'normal' insulation. A single fault in the insulation can
create a connection between the live pole and the cabinet. Without a
grounded cabinet, that could be lethal. With grounded cabinet, you just
blow a fuse.

In case of fire or other damage, the insurance company can give you a
hard time, if they find out that you have class I equipment connected to
a socket without ground.

BTW: the 55 V you mentioned (115 V over here) is more than enough to
blow a serial or parallel port when connecting a grounded printer to a
non-grounded PC. For me, that's also a good reason to ground my PC.

--
Maurice