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

From: der Mouse <mouse_at_Rodents.Montreal.QC.CA>
Date: Wed May 5 01:17:58 2004

> There is no such thing as ground!.


Actually, there is: any sufficiently large object containing equal
amounts of positive and negative charge will do. (The size matters
because in most respects the object in question must be at least
potentially able to accept a substantial amount of electric charge.)

For the voltages and currents involved in this discussion, the only
available object that even approximates that is the earth, but that
doesn't invalidate the basic point.

When working with very high voltages and low currents (which in my
experience has been almost entirely gedanken), I have to keep reminding
myself of that: there is potential current flow whenever there is a
difference in overall charge, regardless of how that difference got
there. For most electronic and electrical purposes, the capacitances
involved are small enough compared to the voltages and currents
involved that we can pretend that an isolated circuit is unreferenced
to ground, but that's merely a handy approximation, not a Truth.

Of course, this doesn't invalidate the point that given decent
transformer insulation, you can ground any single point you please of a
three-phase (whether delta or wye, actually - but grounding other than
the central point of a wye would be Weird). My initial objection was
based on unstated (and incorrect) assumptions....

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Received on Wed May 05 2004 - 01:17:58 BST

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