On Fri, 2 Jan 2004 22:29:59 -0500, Bob Ammerman wrote:

<snip>
>
>Large factories often operate with ungrounded deltas, if any one phase is
>accidentally grounded out the factory can continue operate while the
>electricians search for and repair the problem. Sounds scary, doesn't it!
>

I don't think that it just sounds scary, I think that it *is* scary.

I haven't thought about this for probably the past couple of decades
:=) but that setup reminds me of the 50 volt (IIRC, at 200 amp?)
floating relay supply used aboard Navy destoyers. That supply was used
throughout the missile system for all of its contol switching.

Despite sustaining a direct short to ground on either side of it
anywhere in the system (think battle damage and miles of cabling with
metal sheathing on a metal ship), all of the equipment would continue
to function normally. So long as only one side of it was tied to
ground, everything was still cool. The operative words there being "So
long as only one side of it".

The fecal material would strike the rotating ventilator, so to speak,
if one side developed a ground when you already had a ground on the
opposite one.

Also, two grounds at the same time on the same side made it difficult
as he!! to find either one of them. Disconnecting individual pieces of
equipment and watching for the fault to clear was about the only way
to find them, Two faults in unrelated equipment would mask each other
until you hit the "magic combination" of the right two (out of dozens)
that were causing the problem.

The clearing of any 50-volt grounds that occurred in the system was a
pretty high priority job.

Ah yes, the "good old days". Brings back some fond and some
not-so-fond memories.


Regards, Bob

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