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ttemple
User Rank
Platinum
Exploding meter
ttemple   7/18/2012 10:05:32 AM
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Many years back, I was using an inexpensive digital meter to check for the presence of 480 volts.  It turned out that I had the meter leads in the current measurement positions.  The meter was giving me funny results, and I was getting rather annoyed.  I kept trying to get a reading, and suddenly the meter exploded in my hand.  The front half of the case split from the rear half, and was hanging by some wires.  I had a charred spot on my shirt, and the lead sockets were basically vaporized.

There was photographic evidence taken, and I wish I could find it.  Since I wasn't actually injured, it was a pretty funny picture.  I was holding the exploded meter, with the leads hanging down, with the charred spot square in the middle of my shirt, and a big smile on my face.

Jennifer Campbell
User Rank
Gold
Re: Exploding meter
Jennifer Campbell   7/18/2012 10:18:01 AM
NO RATINGS
Thanks for sharing your story, ttemple. Given your level of annoyance/frustration over the uncooperative meter,  it must have been a little satisying when it vaporized itself! Glad you weren't hurt.

 

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.

gsmith120
User Rank
Platinum
Filament input resistor fire
gsmith120   7/18/2012 12:15:07 PM
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Fresh out of college I was given a filament circuit to design, prototype and test.  One day in the lab my mentor was helping me with something in the lab and for some reason wanted me to apply more input voltage than required.  I remember telling him the input resistor isn't rated for this kind of power.  He said no problem keep going... I kept going... then I said that resistor is getting hot...he said no problem keep going...as the resistor glowed..smoked and then fire... The fire scared him and for some reason seemed to surprise him.  I was thinking I kept telling you that resistor wasn't going to make it.   But to his defense people would be a little jumpy in our lab since we designed high voltage circuits. 

Not really a funny story on paper, it was much funnier to me back then.

warren@fourward.com
User Rank
Platinum
Burned fingers? Sure!
warren@fourward.com   7/18/2012 12:29:51 PM
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I was a marine service engineer while completing my college studies, and I got a call to work on the Mal de Testa, the ship the original Goodbye Mr. Roberts was filmed on.  They had a radar problem.  I reached under the console to feel where the 24VDC power wires were going and my wedding ring shorted out the reverse-biased protection diode was mounted and blew a chunk out of my wedding ring and burned my finger nearly down to the bone.  Yes it hurt.

Now I am careful.  Very careful.  I get to show off my scar from time to time, so it wasn't a total disaster...

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.

tekochip
User Rank
Platinum
Prairie Dogging
tekochip   7/18/2012 12:46:57 PM
NO RATINGS
Too many to list, but here's the biggest.
 
I was working on an electric oven control.  This one was for Europe and ran off of 50Hz.  We didn't have 50Hz supplied to the building, but we did have a rotary converter (a motor with a generator attached) by the docks to provide 50A/230V 50Hz in the labs.  My technician had made a slight wiring error on the control I was working on and I had a dead short across the mains.  I plugged the control into the wall socket and instantly the walls of the building began to vibrate at 50Hz because the wiring inside was vibrating from the dead short.  With a 50A breaker and hefty wiring to handle oven currents, nothing was going to open the circuit.  I tried to pull the plug from the wall, but it only moved a couple of millimeters before becoming welded inside the socket.  Everybody in the building was now "prairie dogging" to see what the source of all the noise was.  I waited a second for the plug to melt a little and then pulled it out another couple of millimeters until it welded again.  I had to do this a couple more times before the plug was clear of the socket showering me with a little splash of molten copper.
 
Since then I always test the controls with a small load and a tiny fuse before stepping up to the real world.


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...

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.

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.

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
Re: Lessen in heat transfer
Tim   7/19/2012 10:31:32 PM
NO RATINGS
Missed that one.  It should be "lesson"

Island_Al
User Rank
Gold
Re: Lessen in heat transfer
Island_Al   7/21/2012 12:18:50 AM
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Years ago I got back from a 2 month field job, wrote my trip report, and sent it to our shop typist/secretary. I then just gave it to my boss. The next day he brought it into my office and it looked like a term paper with red pencil "spelling", "restructure", "needs clarification", etc notes all over it.  It was not a deliverable paper, but just for in-house future work.  I wrote across the top in caps "SEND TO THE TECH WRITER SHOP INSTEAD OF ENGINEERING.  THEY ARE MUCH LESS EXPENSIVE TO USE" and brought it into his office 5 minutes later, dropping it on his desk. I never saw the paper again. I think he just filed it.


Moral of story: Don't let English majors design electronic circuits (or manage engineers). You can't win in a battle of wits if you are half prepared. - Dilbert (paraphrased).

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!

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.

warren@fourward.com
User Rank
Platinum
Re: Spark coil sparks indeed
warren@fourward.com   7/19/2012 1:07:16 PM
NO RATINGS
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.

warren@fourward.com
User Rank
Platinum
This is fun!
warren@fourward.com   7/19/2012 1:18:43 PM
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I use copper beryllium flat spring material as a spring set to move lenses.  I have to cut it to length then drill holes in the corners in a fixture I made.  While holding the fixture and drilling with a high speed Dremel tool the drill bit went through multiple layers of copper beryllium and through my left index finger.  Then the drill bit came out of the Dremel.  I stood there with a drill bit through my finger and my finger nail with equal amounts of drill bit on either side.

I drove myself to the hospital emergency room and held up my finger and told them, "I think I have a problem."  They took me into a room and the Dr. just unscrewed the drill.  I could have done that!

But for the next week I was pulling out little curlicues of spring material out of my finger.  My finger should have been X-rayed, and I should have kept my finger away from the business end of a drill!

Larry M
User Rank
Platinum
Re: Spark coil sparks indeed
Larry M   7/19/2012 1:29:30 PM
NO RATINGS
Warren wrote:  While explaining things he took a metal ballpoint pen and suavely touched the spark in the middle.

Interesting that he had the electrodes exposed. I've built several Jacob's Ladders over the years, usually from discarded 10KV neon sign transformers. They work best if they are in an enclosure vented at the bottom, since they rely on convection airflow to move the arc up from the bottom of the V to where there's really an impressive width.

I've demonstrated this principle by standing above the enclosure and blowing down to hold the arc at an arbitrary spot.

A Jacob's Ladder without an enclosure would only work well if the air was very still.

warren@fourward.com
User Rank
Platinum
Re: Spark coil sparks indeed
warren@fourward.com   7/19/2012 2:04:39 PM
NO RATINGS
I failed to mention that this was in 1966 when the air was still and there were jobs to be had.


bob from maine
User Rank
Platinum
Re: Spark coil sparks indeed
bob from maine   7/26/2012 2:17:20 PM
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Model-T spark coils could, under the right conditions of condensing humidity, energize the dashboard metal each time the #1 cylinder fired. This made for some very entertaining driving. While in the military, we had HF transmitters of various output power all going through one antenna patch panel. Connecting a 10KW transmitter to a whip-antenna with a 1KW tuning coil at its base usually caused the whip antenna to launch at fairly significant velocity. It also occasionally caused the transmitter power-supply to crow-bar and scare the heck out of anyone standing nearby.

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.

Bob Salter
User Rank
Iron
Shock & Burn
Bob Salter   7/19/2012 2:36:43 PM
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I watched a young man, a new hire, operate a drill press for his first job at my plant.  He claimed to be experienced, and after turning on the drill and pulling on the feed lever, nothing was happening. After about half a minute, he let the drill bit retract and was somewhat a little confused and amazed that the end of the drill was a bright red color. Before I could say anything, he quickly touched the end of the bit with his thumb and index finger. The smoke that came off was definately not cutting oil evaporating. I explained that in any metal removing operation, if the tool is not advancing and no chips are being produced, you are definately not cutting. When he asked why this drill did not cut, I asked him if he turned the switch to FWD or REV.

JimT@Future-Product-Innovations
User Rank
Blogger
How NOT to measure the length of a battery
JimT@Future-Product-Innovations   7/22/2012 4:50:40 PM
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In the 1990's in Telecom, before LiIon batteries became the normal standard, NiCad and NiMetal Hydride cylindrical batteries were the cell-phone industry's power-source of choice.  These cylindrical cells, just like Lead-Acid Duracells, were only 1.5V nominal, so typically, three were used to engineer a "cell pack" with a safety circuit. 

The battery department design engineers would routinely measure length of these cells using a metal Vernier caliper.  Guess what happens when you measure across (+) and (-) of a battery cylinder with a metal caliper-?

There was not a Vernier caliper in the entire department that didn't have arc-burns on them, and not an engineer in the department who didn't recognize the "pop" and burnt smell after the failed measurement. It got to be a running joke for the battery engineering department.

Scott Orlosky
User Rank
Platinum
Does the Chemistry lab count?
Scott Orlosky   7/22/2012 8:14:01 PM
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I loved my chemistry lab as a youngster, especially my alcohol lamp burner - you could really get reactions going with a little heat.  One day I was trying to remove the protective metal cap off the top of the burner (i couldn't figure out why it would rust since it was full of "alcohol" and not water).  Undaunted, I grabbed a pair of pliers, twisted for all I was worth and cracked the glass base severing my index finger down to the tendon. Yowtch!  Five stitches later and a bandage the size of a golf ball on my finger - I returned home.  Never did that again.

ervin0072002
User Rank
Gold
6Joule cap fully charged = Pain
ervin0072002   7/23/2012 7:52:24 AM
NO RATINGS
 

Ok so let me define pain in electrical engineering terms. 6 Joule cap charged at about 4kV (do the math if you want to know C I don't remember it) shorting it across my thumb and pointing finger. I had a hard time closing my hand for about a week and had no strength on it for a good two weeks. I know there was some nerve damage but then it went away and did not need therapy.... Of course had I shorted that from one arm to the other I might not be here to tell the story ;)?

Oh and then there is the time when I shorted a capacitor of the same kind that had been sitting in a shelf for over three months. Don't you love capacitors that always stay charged and in case you discharged them they go ahead and charge themselves? Only at a couple of hundred volts but still tickles you if you short it across your fingers...



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