On Sunday, March 6, 2016 at 8:13:13 PM UTC-5, wrote:
On Sun, 6 Mar 2016 16:17:21 -0800 (PST), DerbyDad03
wrote:

On Sunday, March 6, 2016 at 5:52:15 PM UTC-5, wrote:


With alternating current, there is a feeling of electric shock as long
as contact is made. In contrast, with direct current, there is only a
feeling of shock when the circuit is made or broken. While the contact
is maintained, there is no sensation of shock. Below 300 mA DC rms,
there is no let-go phenomenon because the hand is not involuntarily
clamped. There is a feeling of warmth while the current travels
through the arm. Making or breaking the circuit leads to painful
unpleasant shocks. Above 300 mA, letting go may be impossible.4 The
threshold for ventricular fibrillation for direct current shocks
longer than 2 seconds is 150 mA as compared with 50 mA for 60-Hz
shocks; for shocks shorter than 0.2 seconds, the threshold is the same
as that for 60-HZ shocks, that is, approximately 500 mA.4


Based on my "inability to let go" experience while in the USCG, I don't
think I agree with this statement:

"...with direct current, there is only a feeling of shock when the
circuit is made or broken. While the contact is maintained, there
is no sensation of shock."

I was learning how to work on power supplies using a "training device"
while attending the USCG electronics school. The training device was a
microwave sized 300VDC power supply which was set up to easily
accept failed components that the students had to find via systematic
trouble shooting steps. It was basically an open box so that all the
components were in full view. It weighed in at about 35 lbs.

One of the troubleshooting steps was to remove the built in load from
the power supply to see if the symptoms changed. The proper way to
remove the load was to shut down the power supply, remove a jumper -
a short cable with banana plugs on both ends - and then turn the power
supply back on.

I was a cocky kid and to save time I figured I would just grab the
jumper in the middle of the loop and just yank it out. Unfortunately,
the load side of the jumper came out, but the supply side stayed in.
I had my left forearm resting on the case and the open end of the jumper
came in contact with my hand. (4 decades later and the scars are still
very visible). At that point my arm became the load for the 300VDC supply
and my brain did not like it. I couldn't move my left arm so my brain
told my right arm to push the case away. As soon as my right arm touched
the case, I was stuck. I grabbed the 35 lb unit and lifted it right off
the table screaming "Turn it off! Turn it off!" I absolutely could not
let go and I absolutely felt the electricity flowing through my arms
and chest. It was no "feeling of warmth", it was in every way the
"sensation of shock".

But totally different than an AC shock. You had the muscle clench but
it's totally different from AC.

The lines I object to are not related to the muscle clench. I specifically
quoted the lines related to no sensation of shock while contact is
maintained. The article says that no shock will be felt and I sure as
hell felt the shock during the entire time I maintained contact. Up one
arm, across my chest and back down the other arm.



The lab was set up like a classroom and when I started yelling the
guy in front of me turned around and grabbed the power cord to pull
it out of the power strip on my table. Unfortunately, the power strip
just came up with the cord. The guy next to him slammed the power strip
back down to the table and the cord came out. Once the current stopped
flowing through my chest, I literally threw the power supply down onto
the table. Man, was I ****ed.

They took me to the infirmary and did the whole EKG thing. It turned out
that I was OK, other than being pretty shook up and having some bad burns
on both hands. When I went back to class the next day, a couple of things
had changed:

1 - 2 guys quit electronics school after seeing what happened to me.
2 - All the power strips had been screwed down to the tables. :-)

Anyway, bottom line is that I do not agree that with DC there is "no
sensation of shock" while contact is maintained.