[Lab] Open Question: Dumbest Thing You've Done While Making

Richard Guy Briggs rgb at tricolour.net
Mon Jun 24 16:49:38 EDT 2013

On Mon, Jun 24, 2013 at 04:00:51PM -0400, Jason Cobill wrote:
>    Experiments gone wrong? Tools gone out of control? What's the dumbest
> thing you should have caught before you nearly set your house on fire? What
> did you learn from it?
>    Me first: I plugged in a table saw without checking the switch first -
> it was on. And it was covered in 2x4s and sheetwood scraps, which it
> proceeded to launch across the garage and nearly take out a window.
>    It _should_ have been off, but I _should_ have checked. So now I check.
> Every. Time.

Oh, this one's easy.  ;-)    I have two related to electricity.

1)  When I was about 10 I had a power transformer that I had taken out of a
wood-cabinet vacuum tube TV set.  I had learned to solder when I was about 8.
I knew which side was the primary and I wanted to test the secondaries.  I knew
they would be high.  I had a cheap analog multimeter from Radio Scrap with a
750V rating.  I carefully attached and shielded the primary wires to a
standard two-prong plug.  I was sitting on my bed (so no danger of
grounding out, plus it was an isolated secondary).  I pinched one
secondary wire with the meter test lead, then grabbed the second test
lead and went to pinch it with the other secondary...  (It was about 350V.)
	I haven't done that ever again!  Now I used insulated leads.

2)  In my last year of Electrical/Computer Engingeering at U of Ottawa,
I was working on the U of Ottawa solar rayce car RALOS-II, wiring up the
main power backplane of the car (I was the Electrical Systems
Co-ordinator) working on some low-voltage wires on one card that
happenned to be facing a high-voltage, high-current card connected to 7
car batteries in series (90VDC, 1000A?). As I pulled my hands away from
my work something sparked.  Naturally I pulled back, jamming my family
gold ring into the high-voltage card.  Once the sparks stopped, two of
my fingers were black.  After a quick throw of the main power switch for
the car to avoid any further incident, one of my teammates packed me off
to the hospital to clean things up.  On the way to the hospital, I was
babbling with all the wire cross-sectional diameters, materials and
resistances per metre still fresh in my mind, calculating that must have
been a 100kW arc welding burn.  
	I was lucky.  I still have all my fingers, but one has an
interesting ring-shaped scar (that was 20 years ago this month) and the
bloodstone with the family crest in the ring cracked.  I thought of
getting it repaired, then decided to leave it as a reminder.  I was very
lucky it didn't instead hit the iron ring on the adjacent finger that I
had earned not 2 months prior.  Gold is a much better conductor, so it
didn't heat up much compared with the other parts involved.  The two
one-inch spade terminals on the card along with 1/2" PC board traces
vanished.  I had to check a second identical card to find out what was
there.  I earned the nicname "Zot" for that one...
	I now remove my rings when working with high voltage/current.

I still love electricity!  :D

>    -Jason Cobill

	slainte mhath, RGB

Richard Guy Briggs               --  ~\    -- ~\            <hpv.tricolour.net>
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