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Engineers: Have You Ever Burned Off Your Fingertip?

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warren@fourward.com
User Rank
Platinum
Re: Spark coil sparks indeed
warren@fourward.com   7/19/2012 1:07:16 PM
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That reminds me of my high school physics teacher.  He brought in a Jacobs Ladder and had it working on the table while he talked.  While explaining things he took a metal ballpoint pen and suavely touched the spark in the middle.  By my calculations, if the transformer driving it was putting out 20kV the middle of the spark was 10kV.  He got sick leave for three days after it knocked him very painfully backwards into the chalk board.

sensor pro
User Rank
Gold
Re: Burned fingers? Sure!
sensor pro   7/19/2012 11:26:32 AM
while working on Argon Opthalmic laser tubes I also had some problems with my wedding ring. Numerous shorts and also beal diflections. All this until my lead engineer recommended one of two solutions: remove the ring or get divorced.

Well, I'm still married.

OLD_CURMUDGEON
User Rank
Platinum
Burnt fingertips
OLD_CURMUDGEON   7/19/2012 10:45:33 AM
In the early years of my engineering career, I was charged w/ the design of several high power rf (tube) amplifiers.  More than once did I smell the unique odor of "rf-cured bacon" extending from my hands.  After a while, I played it more safely, using an NE-51H neon bulb securely taped to the end of a plastic wand about 3 feet long.  Much safer tool to investigate "hot spots" on the chassis. 

Specific incidents?  Too numerous to mention & too long ago to account accurately.

Larry M
User Rank
Platinum
Spark coil sparks indeed
Larry M   7/19/2012 10:14:26 AM
In my early teens someone gave me a spark coil from a Model-T Ford. This device contains a transformer and mechanical vibrator in an elegant wooden box with dovetailed joints. The vibrator chops the incoming 6 volts DC. The resultant square wave feeds a step-up transformer to produce about 10KV.

I decided to make a Jacob's Ladder by attaching two bare wires configured in a V-shape to the high-voltage terminals. The trick to this is adjusting the spacing so that the arc will jump across the V-gap at the closest point. Localized heating of the air causes the arc to be blown upward across the widening gap.

After three or four power off-on tries at getting the spacing right and having it too far (no arc) or too close (insufficient heating). I decided to try moving the wires while it was on.  Had I picked up a plastic-handled screwdriver from the bench, all would have been fine, but none was at hand. Instead I picked up a plastic-handled hunting knife which was on thw workbench, without noticing the rivets which passed through the plastic handles and blade.

When I touched the hot electrode and received the shock, my arm jerked upward over my head and I released the knife. It flew the 20' length of the workshop and stuck (Jim Bowie style) in a wooden bookcase at the end of the room. I couldn't have thrown it better had I tried.

It was a good thing I was working alone at the time.

Old Man
User Rank
Iron
High Voltage
Old Man   7/19/2012 9:55:10 AM
One of my first jobs I was tasked to build and debug a complex high voltage TWT switching power supply.  The voltages I was working with were +20kV to -20kV and some supplies were as much as 2kW, more than enough to kill you.  I asked my boss what safety proceedures were in place and he told me, "Don't die." (this was a very small company)  As cautious as I was I would recieve mild to moderate shocks most days.  To help prevent the moderate shocks, a technician and I developed the 'wand of power', basically a long plastic stick with a ground wire attached to the end, and used it to pre drain the capacitors before working on a board.  This job was hair raising, electrifying and definately memorable!

MaruaderMan
User Rank
Iron
Re: Lessen in heat transfer
MaruaderMan   7/19/2012 9:38:48 AM
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Sorry to be a nit-picker, but you also need a "lessen" in spelling.

Tim
User Rank
Platinum
Lessen in heat transfer
Tim   7/18/2012 9:58:36 PM
NO RATINGS
As an engineer, i have had my fair share of experiences with errant voltages and shocks from contact with incorrect wires, but my only real injury was due to inexperience when I started my first job out of high school.  At the company, rookie engineer projects were usually completed through the build process with the engineer working with the necessary support personnel to physically complete the project.  My design called for a bracket of steel bent into a certain angle and then drilled and tapped.  The technician that I was working with explained that they usually complete brackets like this by heating the bend point cherry red and attaching a clamp and bending the bracket into place.  I said no problem and the tech left for break.  I attached the clamp, began heating the steel and when it was cherry red, i grabbed the clamp and immediately learned that heat transfers through steel quickly.  I missed the step that stated to attach the clamp after the metal was hot.  I still have the burn scars to remind me of the heat transfer capabilities of steel.

Charles Murray
User Rank
Blogger
Re: Exploding meter
Charles Murray   7/18/2012 5:25:49 PM
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ttemple: "...holding the meter, with the leads hanging down, with the charred spot square in the middle of my shirt..." Sounds like a classic Wile E. Coyote picture. The only part missing was the burn marks on your face.

NadineJ
User Rank
Platinum
Where to begin?
NadineJ   7/18/2012 2:02:37 PM
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The fact that I have all ten fingers is remarkable.  I'm always amazed when my fingerprints reappear.

I've defintely burned and sliced off my finger tips several times.  I think it all started when, at the age of 12, I put a sewing machine needle through my right index finger.  All of the adults panicked but the nail eventually grew out.

akili
User Rank
Iron
Exploding Switchboard
akili   7/18/2012 1:16:37 PM
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I had a problem with the 100A three-phase feed to the earth station servo system. I traced the problem right back to the main station distribution switchboard, well beyond my pay-grade at the time.  With the chief electrician in charge reading out the maker's instructions I followed his every word to remove and inspect the contact carriage. According to the book by means of a "special feature" it was supposedly safe to do this operation off-load but with the rest of the switchboard on-line.  We had never used that brand of switchboard before and we took the instructions at face value.  "Remove locking screw A" - OK.  "Raise latch lever B" - OK.  "Grasp carrier firmly, lift and pull out" - BANG!  When our eyes and ears returned to normal I was unhurt and had not received an electric shock but my hand was covered with that lovely bronze sheen from vaporised copper.  The switchboard was wrecked and we never used that brand again.  Surprisingly they are still in business.  No names, no pack drill...

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