Larry wrote:
chuck wrote in news:1150376821_9981
@sp6iad.superfeed.net:
ABYC and common sense would have you ground the
neutral of the isolation transformer secondary and
use that as your equipment grounding conductor.
That way you remain isolated from the AC systems
of the rest of the world, but you maintain the
safety benefit of equipment grounding. Even GFCI
protection on the secondary wouldn't work without
that ground. You don't need the green wire for
GFCI to detect a ground fault, but you DO need a
connection to "ground" for a ground fault to
occur. So if you leave off a secondary ground, you
prevent ground faults by allowing the hot wire to
short to an equipment cabinet undetected! Not
likely to be very popular, Larry.
If the equipment on my bench is plugged into my fully isolated isolation
transformer, touching either (BUT NOT BOTH) sides of the line is no shock
hazard whatsoever, the very reason for the isolation transformer in the
first place. No equipment ground is necessary.
The isolation transformer on my bench provides an
equipment grounding conductor on the secondary
side and also the ability to measure leakage current.
"Ground" is just a point, a reference, that's way overrated....and
misunderstood. Voltage never killed anyone...Voltage DIFFERENCE does.
I looked for a video I had on my old computer that was posted from a
power company. The subject of the video was the guys who fly around very
high voltage transmission lines in a helicopter, drop off a man hanging
from that line, to replaces some of the gear on the hot end of
insulators, FROM the hot end of insulators you can only get near if you
are already at that potential, several hundred thousand volts above
"ground". The most impressive part of the video is the guy sitting on
the little platform beside the helicopter's skids with a buzz stick in
his hands sticking out as they approached the line. The high voltage
reaches out 10's of feet in a fairly amazing arc to the end of the buzz
stick until the helo gets close enough to actually attach the helo's
chassis to the high tension power line, putting them both at several
hundred thousand volts off "ground" so men and parts can be transferred
as the expert pilot holds the helo rock still against the line.
Sorry I can't find it in the stacks of CDRs and DVDs piled around here.
It was a great movie to watch. JUST DON'T TOUCH GROUND WHILE YOU'RE OUT
THERE AND YOU'RE FINE!...(c;
It's all about your "reference"....
Just a few last comments.
Basically the world doesn't like the idea of hot
wires shorted to our equipment cases. But worse
than that, they don't like for it to happen
without some thing alerting us to the problem or
correcting it.
With your two-wire, groundless system, I know of
no way to detect and/or clear such a short. Your
proposed system effectively says: leaks happen.
Don't ask and don't tell. We've tossed the
equipment grounding conductor and now we're free
and safe.
But as I have said, GFCI will not work with your
system if there is no "ground". Yes, yes, the
device doesn't actually require a connection to
the equipment grounding conductor to work. But
there must be a ground for a ground fault to
occur! Otherwise there is no differential current
for the GFCI to detect.
Actually it is sometimes difficult to avoid
grounding an appliance case. Then what? What about
lightning protection?
I understand that you're making the point that the
use of grounding and bonding per the NEC is
sometimes the cause of problems. But the system is
what we have, and it prevents an awful lot more
electrical injuries than it causes.
Chuck
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