On Thu, 24 Jul 2014 11:52:46 +0700, John B. Slocomb
wrote:

On Wed, 23 Jul 2014 22:24:22 -0500, Martin Eastburn
wrote:

On 7/22/2014 11:21 PM, DoN. Nichols wrote:
On 2014-07-21, Martin Eastburn wrote:
On 7/20/2014 7:50 AM, Larry Jaques wrote:
On 20 Jul 2014 00:52:54 GMT, "DoN. Nichols"
wrote:

[ ... ]

And, while the initial resistance will be a function mostly of
the moisture and salinity of the hands contacting the voltage source,
once the initial current starts to flow, the skin breaks down and the
resistance drops rapidly -- and the more the voltage, the more rapidly
the resistance drops. And the current needed for a fatal dosage is well
below the trip current levels of commercial circuit breakers. (I do
have some glass cartridge fuses rated at 1/100 Amp (10 mA) which should
be enough to protect you -- but not enough to allow most equipment to
operate, so that is why I still have those fuses unused. :-)

Anecdotally, 240 is safer because it will kick you off more quickly
than 120v.

Yes -- depending on the orientation of your hand. If you touch
the palm, you are more likely to grip firmly onto the source of the
electricity and soon be deal.

If you fall into wires and complete the circuit, you'll be
dead more quickly, but brushes against it are, IMHO, safer, and I'd
rather work with 240 than 120 for that reason. 5mil nitrile gloves are
a part of my DVM package, and I wear them when working with live
circuits. You can feel the voltage start to bite through them and
move your mostly-water body parts quickly out of contact. When
convenient (maybe 1/4 to 1/3 of the time), I shut off the breaker.
I have a healthy respect for deadly but wonderful electricity.

CAVEAT: Kids, don't try this at home.

Amen!

My worst zap was from a 2 KV bank of capacitors (200 uF total)
connected to a pair of transformers which could recharge the caps in 100
mS from a full discharge. That one got me from my index finger on my
left hand through my body to the right elbow (which was resting on a old
Tektronix tube 'scope. I spent what felt like five minutes looking for
my heartbeat, before I realized that that noise which was getting in the
way *was* my heartbeat. Sortly after that, I arranged for the whole
team to get CPR training. :-)

--
Liberalism is the result of severe pathogens in our society.

I had a friend years ago who's dad was a licensed electrician. Actually
2. Taught Electronics and dads push the 'new' stuff on the kids.

Anyway he was working in the Engineering building and with the cover off
a 880v 3 phase box - he was working the box hot. Normal. Power down
all sorts of expensive machines on those lines... He dropped his
screwdriver down into the panel. Vaporized the steel, plated his face
and upper body - his glasses in side of his goggles saved his eyes.
He was in tough shape for a month or so at the hospital.

Ouch!

Yes, sometimes, it is necessary to work on live circuits -- as
the only way to tell what they are doing. But when there is *that* much
power, I would really prefer to find some other way to do it. :-)

One has to be careful. Now they sell Be metal drivers and coated drivers.

O.K. I have to ask what the benefit of the Be (I presume
actually BeCu non-sparking tools), but I can't imagine the vapor from
them falling into a high power arc would be that much lower in
temperature, and given the hazards in machining BeCu, I can't imagine
that the vapor from that would be any too healthy compared to vaporized
steel.

The real place which I know of BeCu tools being preferred is
when working in an explosive atmosphere, as they don't generate
sparks when they hit other metals, while steel (especially hardened
steel) does -- thus being likely to ignite the explosive mixture.

Enjoy,
DoN.

IIRC BeCu tools are non-conductive. They won't cause an arc (explode
gas) if shorted across terminals.

We used bronze in the paint shop at GM, but that was in the late 60's.
I was plant security the summer between college and contract work.

Martin

Nope. Beryllium copper alloys are high conductive materials.

Bronze is an allow of Tin and copper.

Alloy is not spelled "allow", even when it contains beryllium :-)


The U.S. Air force once issued beryllium copper tools for work on
airplanes as they are non-sparking. Sometime later they went to great
lengths to recover them from all tool boxes as the beryllium was said
to be toxic. I definitely remember the notice that Beryllium copper
tools were to be immediately turned into Supply for replacement.


--
Cheers,

John B.