[Elecraft] Mistakes (WAS: One more on the "stupid" thread)

[tom.w3qs]

Love this thread, makes me feel more 'normal'.  However, from an earlier
post... 

-----Original Message-----

"... In power supplies the mains voltage is absolutely deadly."

The father in me yearns to leave this alone, but the physics teacher in me
requires me to set this record straight.

Except in pretty extreme circumstances, mains voltages (in the US where the
mains run around 117 VAC) are not generally considered fatal.

As we all (should) know, it ain't the voltage that does ya in, its the
current.  While it only takes about 24 volts to push a fatal current, it all
boils down to Ohm's Law.

A typically healthy person has a normal body resistance of about 100,000
ohms (a pretty low estimate), and across a 117 volt line, that's only about
0.0012 amps, a bit more than one milliamp, which is not a fatal current.  It
should take 50 times that much (for a second or longer if through the heart
or brain) to do a person in, although you can certainly feel 1 milliamp!
Even considering that 117 is RMS, and the actual voltage can be as high as
170, you should still be safe.

Now, all bets are off if you're standing in a pool of water or are drenched
from rain, or do everything else wrong.  

Best advice I ever got was from an old navy chief (when I was a young
radioman), to wit:  "One hand for the Navy, one hand for yourself".  IOW,
when working on anything that could possibly have live current, keep one
hand behind your back.  Completing a circuit with both hands puts your
pumper in the circuit which is powered by electricity.

Tom