VAX Cluster on Ebay in OK (was Re: More DEC equipment spottedin

From: Patrick Finnegan <>
Date: Tue May 4 23:50:41 2004

Tony Duell declared on Tuesday 04 May 2004 10:53 pm:
> > > There is no such thing as ground!.
> >
> > Sure, there is. It's the voltage potential present on a long
> > electrode inserted into the earth. :)
> And just what do I connect the other lead of my voltmeter to? :-)

Ground. :)

> Incidentally, 'There is no such thing as groud' is one of Voanda's
> laws and has 2 meanings. The first is the one I am using there, that
> voltmeters have 2 leads, and it's arbitrary where you connect the
> 'refernce' lead to.

I was speaking in an electrician's sense, not as in an engineer's sense
of the word.

> The second is that any real connection has impedance, and that the
> 'ground' in a high-speed digital circuit may not be quite the same
> voltage everywhere. In fact 'ground bounce' -- mostly due to the
> inductance of the ground connection -- is a problem in laying out high
> speed circuitry.

That doesn't apply as much to AC power wiring, though you still have to
watch for "ground loops" where there's a potential between two different
grounding points due to resistance, which will be carried over signal
cables. Still, that's not something the electrician usually cares

Purdue University ITAP/RCS        ---
The Computer Refuge               ---
Received on Tue May 04 2004 - 23:50:41 BST

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