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eA near miss <Zap!>
From: Gary Lau 21-Nov-1997 1019[SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Friday, November 21, 1997 8:28 AM
To: tesla-at-pupman-dot-com
Subject: A near miss <Zap!>
I had a near-miss about a month ago that upon further thought, might benefit
others to share it.
I was tuning my coil, moving the primary tap from turn to turn. Since it
involved screwing and unscrewing a clamp on each iteration, it was difficult to
accurately compare the arc length at each position, so I thought it might be
better to tape the end of the wire to the end of a long pole and drag the tip
from turn to turn, noting where the arc is best.
When I did this, each time I broke the connection, a rather fierce flaming arc
was drawn, and fearing that I might damage something, quickly put down the wire
and turned off the power. Back to plan "A", fasten the clamp to each turn and
make that subjective decision which is best.
Upon picking up the loose wire from the cap, I received a startling shock. I
don't recall whether I had one hand on the primary and the other on the tap
wire, or one hand on the concrete floor, or none of the above, but I do realize
that I was lucky and that it could have been MUCH more severe, if not fatal.
Normally with the tap wire connected, any charge in the cap after turning off
power would be shorted out by the DC path through the primary and transformer,
but in this case, after drawing an arc through the cap and then it being
open-circuited, an indeterminate charge was left on it. An easy thing to
understand in the clarity of hindsight, but not something I thought of at the
time, being used to the cap being safe when power is off.
I hope someone else may benefit by my near miss.
Gary Lau
Waltham, MA