On 12/5/2010 3:42 PM, email@example.com wrote:
In my experience, high frequency AC hurts worse than any other shock
I've had. The horizontal output of old tube type TV sets can make you
feel like you've been turned inside out. It goes to the bone. :-)
While working on the LORAN transmitters I mentioned above, I witnessed
a guy come as close to death from electrocution as you can get.
When you removed any of the 3' x 3' panels from the side of the
transmitter, a spring loaded interlock grounded all high voltage. If
you then removed any of the grounded bus bars from the big oil filled
caps, you were required to attach a grounding strap across the
terminals to prevent the caps from charging back up from the energy in
the room. (There was always 1 live transmitter in operation while we
worked on the standby)
A tech had moved a cap to the workbench, shorted it out, and then
later put it back into the transmitter. He removed the grounding
strap, then got distracted and didn't hook up the bus bars. After the
cap had been sitting open for a few hours, he stuck his upper body
into the transmitter and reached across the cap. His chest came in
contact with the 2 terminals and it threw him upward into the bottom
of the shelf above, which bounced him back down onto the cap, which -
not having been fully discharged yet - threw him back up into the
upper shelf one more time.
This time he came down on the cap and sort of slithered to the floor,
almost unconscious and very bruised and battered.
We were 60 miles above Nome, AK, so we had to call in an air-taxi from
a nearby village ("nearby" was 15 miles across the Port Clarence Bay)
to come get him and take him to the hospital in Nome.
I was going to post the same thing. I've worked on a lot of video game
monitors. They all have a hot chassis with about 130VDC to ground
(always run them through an isolation transformer) but from that hot to
the HOT (horizontal output transistor) is what gave me quite a few
burns and the smell of burning flesh. I think it does hurt more than
any other shock, and damn, it grabs you and doesn't want to let go.
Most of the shocks I've encountered ran from one hand to the other...
with my heart in between. Either I'm lucky as all hell or that thing
about the one hand behind the back and the current going through your
heart is just a story.
I think my worst ever shock was _only_ 120VAC from my pliers with sweaty
hands, onto a hot wire, through me and to ground through my sweaty
forehead. It went through my head, I did see a very bright flash, I
suppose when it went through my eyes and the nerves for them. I had the
machine unplugged and a good Samaritan plugged it in for me.
One of my little brothers was very helpful by cutting off the little
plastic nub made when my insulated pliers were dipped in plastic. I
suppose he thought it should be more symmetrical. I got the crap zapped
out of me when I grabbed a hot wire with them.
Yeah... Having done a lot of lighting work in commercial buildings,
I always touch the hot wire in the fixture to a ground before I work
on anything inside it (for other than re-lamping) -- this does two
things: one, it either lets me verify that I was successful in
locating the correct circuit and two, if I did not locate the correct
circuit, I now have a tripped breaker to help me locate the means
to re-energize the fixture after I finish working on it to know where
to kill it the next time...
It is often difficult to locate the correct breaker for a light
that has either burn out lamps or a non functional ballast...
You have no positive indication that the power is off as the light
was not lit when you started...
Well, there is a new requirement for disconnects in light fixtures now.
It's a little plug an socket set that you just unplug for service. It
seems a lot of maintenance people were getting hurt or killed while
servicing 277 volt lighting. Just about every electrician I run across
on a job will cut the things off and use a wire nut. SOP for me has been
the installation of a fuse holder and fuse. One on the hot wire
for 120 volt ans two for 277 volt lighting. It serves a dual purpose
of disconnect and keeping the magic smoke inside the ballast. I see from
your post that you use the Jesus method to find circuit breakers. :-)
Dunno. My last "tickle" was actually the worst jolt I've ever gotten,
one I won't soon forget.
Was working on a friend's shop in a commercial space in San Francisco,
installing lights. Somehow contacted two wires that I *thought* were
disconnected but weren't. What I didn't know at the time was that these
weren't 120 volts, but instead were 277 volts.
Big difference. Big buzz. I was on a stepladder at the time, and am
*very* lucky I wasn't thrown clear off.
I heard of a bald electrician who was working on 277volt lighting when
he raised up while making a connection and his bald head touched the
fixture. R.I.P. A lot of guys are hurt or killed working on 277volt
lighting circuits because they're not careful enough.
I've had more than I can count, and I become more careful with each
I've gotten them from electric fences.
I've gotten them from automotive ignition systems (capable of over
I've gotten them from electronics - including TV High voltage
I've gotten them from 115 and 230 volt AC mains
re: "I did vaporize in half a pickup dipstick..."
As part of the Safety Training for new arrivals at the Loran
transmitter sites I mentioned earlier, we came up with a way to keep
the non-electronics personnel out of the transmitter building.
All we needed was a huge oil filled capacitor, a Hi-Pot power supply
and a Dead Man stick - AKA a grounding rod: a long wooden handle with
a metal hooked rod threaded into it and a braided grounding strap
attached to the rod. It's main purpose was to tap around inside the
transmitters once they were turned off to make sure there were no
stray valotages hanging around. Their secondary purpose was to hook
the clothing of anyone unlucky enough to get stuck inside a powered on
piece of equipment and pull their dead, smoking carcass out so we
could get back to work.
Anyway, as part of the newbie tour, we'd let the guys peek into the
transmitter room and then close the door. We'd then explain to them
that the machines on the other side of the door wanted to kill them
and they they should never to go into that room without a journeyman
Then we'd take a big oil filled cap, hook the grounding strap of a
Dead Man stick to one terminal, use a Hi-Pot to charge the cap up to a
couple of KV and, right after turning the lights off, we'd tap the rod
to the other terminal, shorting out the cap. The resulting CRACK and
sparks were enough to convince them that they didn't want to hang
around inside the transmitter building.
Well, one time we got a little ballsy and charged the cap up a bit
higher than we normally did. When I tapped the rod to the terminal,
not only was there a CRACK that sent even the most seasoned of us
running, it split the hardwood handle and shot the metal rod halfway
across the room.
After we calmed down, someone realized that there was a good chance
that the cap was not fully discharged, so he grabbed another Dead Man
stick and shorted it out again. Good thing too. We got a decent CRACK
out of the second try, but nothing like the first.
Me and the other broadcast engineers I know refer to them as
"Jesus Sticks". When you ground something with it that has a
high potential, you shout "JESUS!" when it explodes. The other
explanation is that the safety device keeps you from going to
Jesus but all the guys I know who work on electronic gear are
all going to meet the other guy. :-)
On Thu, 02 Dec 2010 19:09:17 -0500, firstname.lastname@example.org wrote:
Ground itself has significant resistance -- that's why grounding rods
require a lot of ground contact, a great deal more than the tiller
blade. And it's not certain that the tiller blade would even have good
ground contact. And unless the grounding is adequate to reduce the
voltage potential, it does not affect the shock given. Since the
poster hit an entrance cable, the breaker was at the transformer and
was probably several hundred amps at least.
1 mA is enough to feel, and 100mA is enough to kill.
Human body resistance may vary from 1000 ohms (wet hands) to 100,000
ohms. (Numbers from a Wikipedia article, so take it for what you think
it's worth.) Assuming a 100V shock (one leg), at the highest
resistance the shock would be felt, and at the lowest resistance,
electrocution is a distinct possibility.
My favorite method of popping a circuit breaker, I have seen this.
Wire the light switch and the light in parallel. Need to turn off the
light, just throw the switch. Turning it back on is slightly more involved.
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