Re: 60V DC dangerous?

On Sat, 08 Jul 2006 11:14:14 -0700, John Larkin
<jjlarkin@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> Gave us:

I've been doing a lot of AC wiring in our "new" building lately, and I
usually do it hot.

I usually do shut down if no other devices are affected, but i have
done several kitchen jobs with the breakers on because I didn't want
to have the refrigerator loose (gain) thermal energy.

120 AC isn't a big deal if you do happen to touch
it.

The trick is to be smart enough to a: never touch it, and be make
touching it a non issue, should it happen. If you are "floating"
there will be no shock. There may be a very small influx of electrons
to charge you up like a very small capacitor, since you are above
ground potential, but that's it. Also, that would have to happen
right at the peak of the cycle, and gets nullified 1/120 th of a
second later.

You can hand-twist the hot conductors before scrunching on the
wire nuts, with just a bit of forethought.

Yes... well America is known for accommodating ALL user types when
setting a standard or educating someone. So they teach no live
circuits and a hand in a pocket. etc. You and I can work hot, but not
all folks that get into this industry has that much "presence of
mind".

Even we can make a mistake. Sometimes, you only get to make one.

Regardless of what one teaches, one should always teach that as well.
The best philosophy is that one only gets to make one mistake. This
reinforces the risk in one's mind, even if the level is false, it is
safer.

It's like ESD: if you
handle things right, you don't need a lot of special gear.

Keeping one's self "balanced" to ground potential works. If you are
standing still. Walking across a room with an fpga chip in hand
whether pins up or pins down is dangerous for the chip.

Ever heard of "infant mortality"?

I wouldn't want to build something or repair something that is
designed to keep men alive, or to save lives knowing that one event
(which you cannot see) might lead to an early failure in the field at
a critical moment. If all that worked in the industry took the correct
steps to ensure that no such event occurs, we would all have products
that last for a very very long time. An ESD event doesn't have to
cause an immediate failure mode to cause damage and be the root cause
of a future failure..

I'd imagine that hot-wiring 230 volts would be a little more
interesting.

I will not work at those levels hot. Even I know enough not to play
with matches at a gas station.

I would create and test products that make much higher voltages, and
then operate them live, but there are several procedures in place for
such bench operations. We did DC to DC converters for outputs from
250 x 2 (plus and minus) to 400kV units over in europe for
transmitters (the most we did here was 180kV X-Ray supply for an
airport scanner. The tube alone was $900 each, made by some famous
German doctor/xray tube maker)

Anyway, HV stuff like that gets fired up inside cages with no persons
inside at the time. All setups for loading and metrics have to be in
place. The most we have run in an open lab or on an open bench is
50kV. I worked with 15kV to 40kV practically daily for years...
not anymore though. Now I convert HV into little tiny powerful
waves...
.

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