Engineering Horror: Shock of a lifetime

10/11/2012 7:33 AM EDT

occupational Hazard. similarly when i was working with my new elecronic ballast unknowingly my hands came into contact with 230 volts a.c. phase and neutral. A big shock. The hands moved out automatically. In my brain i felt the 3D images of all my organs in my body area.For about 3 days i felt little different then i become normal.

10/11/2012 1:01 PM EDT

I was developing a new space-launch range safety radar transponder in the mid 1980's. The power supply was at the bottom of the board stack and distributed the low voltage DC as well as 350V to the boards above it by a series of exposed pins that plugged into the bottom of the connector strip on the next board. That is, they were exposed only when the cover was removed. Well, one somewhat fatigued evening, the company's president was in the lab working with another engineer, and asks me if I was still using an oscilloscope. I was about to reply "yes" as I firmly grasped the chassis and board stack to take it apart. Without turning off the power supply. After I managed to let to of the board stack and slumped back onto the lab stool to catch my breath, he remarked "No, I think you're finished tonight."

10/11/2012 11:17 PM EDT

I remember back in the "old" days, we used to have to manually align the read heads on the 'washing machine" type hard drives, you know, with the 10Mbyte (yes, 10 Mbyte not Gbyte!)removeable platters. Well the adjustment had to be done with an allen key to move the heads, Unfortunately it was difficult to get to, and the heads were positioned just above the power supply capacitors (BII..IIG capacitors). One of our techs was working on one machine, head down, when he accidently touched the capacitor terminals with his metal watch band... Smell of burnt flesh and a welded watch band!

10/12/2012 1:25 PM EDT

I grew up in a 220VAC country, and the electricians there used to check the 'live' status of a circuit by flicking a finger across the line. I hope that is no longer the accepted practice, but I remember doing that myself and it wasn't too bad---if done properly the shock would be minimal and very short.

Here in the US I have heard this electrician's joke: "What is the difference between a 120VAC and a 240VAC circuit?" "The 220VAC hurts more".

10/12/2012 7:40 PM EDT

I was proudly demonstrating my new transmitter to my sister when I was age 11. The output rectifier fed into a 32 uF smoothing cap at 240 VAC. I turned it off, but of course there was still charge, and I accidentally brushed the hot terminal while holding the case. POW!! I flew backwards through the air, landing on the other side of the room. The bad news was that she laughed for the longest time. The good news was that I landed smack dab on the bed, uninjured!

10/12/2012 11:41 PM EDT

FYI: There can be serious delayed effects from an electric shock. Although still being alive is a good sign, after a moderate or severe electric shock you should contact EMS.

10/13/2012 9:45 PM EDT

Quite a few years ago I was working on the startup of an industrial test machine that used 480 volts, 3-phase power. This was our first machine to use a STD-bus computer system, and the control computer card rack was just a few inches below the disconnect switch. Late in the afternoon, as I was reaching for the reset button on the processor card, the back of my hand touched a terminal on the disconnect switch. I jumped about six feet backwards and jumped up and down because of being startled so much. That scared my co-workers quite a bit. I had to explain that the time to be scared would be when I fell down and was silent.
We did get a plastic shield on those temporary connections after that incident.

10/15/2012 3:07 PM EDT

I built a Tesla coil when I was about 15. I used a 7.5 KV @125 mA neon tube transformer to drive capacitor bank. The HV was switched to the 10T primary of the Tesla coil through a spark gap. The secondary was a 4 foot long piece of carpet tube with 2000T of #31 wire in the center of the "squirrel cage".

I didn't know too much back then so I had to experiment a lot to optimize performance. I ended up being able to achieve a 3 foot arc.

My most difficult problem was the spark gap. I burned up steel, graphite, and copper until finally settling on 2 chrome-plated balls salvaged out of a WWII lightning arrestor.

The noise from the spark gap was deafening while sparking but you only heard a slight hum from the transformer when the gap was too large. My older brother came into my lab/bedroom while the gap was open and asked, "What are these?" (Oh! Shiny!) He grabbed a ball in each hand before I could stop him. He hopped/danced around the room for about 20 seconds before he recovered.

He was lucky to have survived. Where was a camcorder when you needed one?

10/22/2012 2:12 PM EDT

Sounds like a lot of readers had their experience when quite young, as I would expect. I got to shake Mr Electron's hand in my early teens. Back then, I was obsessed with strobe lights after visiting a particular exhibit at the Canadian National Exhibition in Toronto. My first attempt was a contraption consisting of a lightbulb in a box with a rotating shutter in front of an aperture. I eventually graduated several years later to Xenon flash strobes, after eagerly reading through all the published construction projects of the day. I built a strobe light using a flash tube and trigger transformer salvaged from a broken flash unit. The B+ was doubled line voltage, which reached almost 340V, stored on a 10uF 450V capacitor. Although I was aware of the danger, some clumsy handling one day in my lab/bedroom blew me back on my chair and, luckily, onto the bed behind me. I was thankfully uninjured, and the experience gave me a fortified respect for high voltage that I carry to this day.

12/26/2012 6:11 PM EST

"Shocking! Positively shocking!"
-- James Bond (Goldfinger)

I remember as a pre-teen using two knives to get a piece of toast that was stuck in the toaster. It felt like a pulse, as if an expanding wave, went through my arms and chest.

Another time I blew a fuse in the fuse-box in my basement "lab" when I tried to wind my own transformer. My father asked me not to do that anymore.

In high school, while up on a ladder checking fuses on the gym's malfunctioning basketball scoreboard when I thought it was turned off, I unscrewed the cap and got zapped when I grabbed one of the fuses. I distinctly remember my body's automatic reaction: my arm pulled back and threw that fuse away as hard as it could, no thinking required. I managed to stay on the ladder.

"They say God protects children, idiots, and drunks. I know this to be true, for I have tested all three on many different occasions."