A little anecdote to this thread:
When I was an apprentice in engineering college (UK Military, in the 60's),
I had an instructor who's job it was to teach us "basic electricity". Back
in the barrack block in the evenings I was building my second radio
transmitter. It delivered 40-Watts, using an 807 final stage.
During one of the first daily lessons the instructor, a Flight Lieutenant
Barker, told us:
"Current cannot flow unless there is a complete closed circuit. If I had a
source of voltage: two contacts with 1000 Volts between them, then I could
safely touch just ONE contact and not feel anything at all. I could only get
a shock if there current flowing from one terminal to another, or Earth."
The following day we all sat in the classroom, and the following
conversation took place:
FS: "Lythall! What IS that hideous contraption on your desk?"
ME: "Yesterday you said that if you had 2 terminals with a 1000 Volts ..."
FS: "Yes, but what is that to do with that - er - THING on your desk?"
ME: "This thing, sir, is a 350v-0-350v mains isolation transformer and there
are 700 volts between these two terminals, here. Yesterday you said you
could touch them and not feel a thing."
Old "Barky" (although he was quite young) was quite brave and took up the
challenge. He used a 1000v Bridge MEGGA to check the primary/secondary
isolation, then he wired 3x mains light-bulbs in series and connected them
to the secondary. He stood on dry wooden duct-boards, and a rubber mat, and
then plugged in the transformer. He measured the voltages with an AVO for us
all to see. He put one hand in his pocket and touched one terminal with his
other hand. Nothing! He was most definitely alive. He then moved his hand to
touch the other terminal, and with a painless grin on his face, yet these
three 240v lamps were still grinding red-hot.
FS: "Now Lythall, do you believe that I can safely touch one terminal?"
ME: "Yes sir!"
FS: "Do you have confidence in my teachings?"
ME: "Yes sir!"
(Then with an evil glint in his eye he said:)
FS: "Good! Now Lythall, it is YOUR turn to come up here and show the rest of
the class just how safe it is. You can repeat what I have just done."
Those were the days! There is no way a teacher could ever use such teaching
techniques today. But we all learned a lesson that day. Although I was quite
advance, far ahead of the other students, thanks to Amateur Radio, I still
learned to treat instructors with respect. I also gained a lot of self
confidence, for a mid-teenager.
Best regards Hairy Lethall - oeieio(at)hotmail(dot)com