On Thu, 2010-02-18 at 21:53 -0500, DAVID HELLER wrote:
I too do electrical power consulting work, and, like Jerry, have been on
cases involving poorly-trained people working on hot stuff - and it's
never
fun to reconstruct the blame where severe injuries or fatalities are
involved.
Sometimes its not been the poorly trained, its been the poorly
maintained tool or work place and the deceased didn't do anything wrong.
I have testified in depositions (involving other products problems as
well as fires accused to be of electrical origin) about 200 times and in
court about 75 times. I think I have given up that line of work, I hope.
Between graduation and grad school I did a stint as Jr.Engineer for an
electric utility - and whether beginner or old timer safety was preached
day
in, day out.
My first job out of college was at Collins in the BC and high power
transmitter department. We kept test voltages under 100 KV peak and
radio operating voltages down to 60 KV peak. And we spent much time
discussing safety and worked safely. The Collins 821A-1 was pretty good
though a couple of us found 900 volts where it was a hazard without
protection. Burned a hole in my left index finger all the way to the
bone and raised the pitch of my voice about two octaves for a couple
days. My left elbow was grounded.
Richards' laughing friends are the stupid ones. Do it yourself is fine
for
many things, but not power-electric. I hate these home-mechanic books
explaining how simple it is to add an outlet, etc. Fine IF and ONLY IF
you
have had the equivalent of an apprenticeship - or degrees in EE with a
bit
of hands-on experience - or - adequate fire and life/health insurance.
With care its not all that hard, if you believe ALL the book tells you
about connections and wire colors but even electricians some times don't
understand the need for separate ground wires since by their
understanding of circuits the safety ground adds nothing to the circuit
function or safety. Just that when the metal case of the tool is
grounded to the return wire (neutral) and that wire breaks the tool case
is now at 120 volts with the impedance of the motor in series. When it
only takes 50 milliamps to put the heart into fibrillation, the
impedance of a 7 or 15 amp series motor has no effect on the current
through the heart.
Even with supposedly qualified electricians doing the work I've seen too
many installations that are booby traps, and too many of them have been
sprung before I get to see them.
Suggestions to all: two things to avoid: adapters for 3-prong 120 plugs
to
old style 2-prong (ground terminal cut off is same thing), and the
all-too-common in residential construction: blue plastic junction boxes.
I call those adapters "ungrounding adapters." And I live in an old house
with two wire wiring. I use them on occasion, but I know the condition
of the tool I'm using them with, usually is also double insulated and in
a dry place. There are three wire outlets here, but only the circuits
I've added for computers and hamshack in the basement and for work in
the garage have proper grounds.
Unfortunately plastic for junction boxes and conduit is approved by the
NEC. I prefer steel for junction boxes and for all wiring to be in steel
conduit. The makers of plastics have convinced the NEC committees that
plastic holds in arcs and holds out fires adequately and certainly in
wet applications plastic can last longer. In steel conduit I want a
separate copper safety ground conductor in all pipes and all circuits
and that can't be left out of plastic. I don't want to depend on the
conduit connectors for my safety.
Will Jerry back me up?
Dave K3TX
73, Jerry, K0CQ