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Sherlock Ohms

Staying Safe From High Voltage

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tekochip
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Platinum
Chicken Stick
tekochip   2/21/2014 9:30:45 AM
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It's been a while, but I remember those, as a student it frightened me that there would be enough energy in the air to illuminate the bulb, and we sometimes called the tester a "chicken stick".  The neon bulb tester was a handy little gadget.  I had one that also had leads and would use it at gigs to see if all the amps were grounded properly.  You could touch one side to the chassis and let the other hang in the air to see if the ground was correct.  The cords were all two wire and a switch on the amp would flip the chassis to be AC coupled to one side of the mains or the other.  Guessing the wrong polarity would make you mighty uncomfortable, especially if you bumped into a sweaty lead singer or other similar stage prop.


al_phelps
User Rank
Iron
Arc tuning
al_phelps   2/21/2014 11:53:49 AM
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As a young Aviation Electronics Technician in the Navy I remember using two different tuning aids we used to peak the output of the ARC-1 HF transmitter. The preferred tuning aid was the flourescent lamp from a bunk light, a small flourescent tube about a foot long. When held close to the output terminals of the transmitter, it would glow, the transmitter would then be tweaked for the brightest glow. The second method was using an ordinary wooden pencil, with the metal band and eraser removed. The pencil when held close to the terminals would draw an arc, adjusting the transmitter for the brightest arc. Sometimes when you were in the field, test equipment was not always available when you needed it.

bob from maine
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Platinum
Re: Arc tuning
bob from maine   2/21/2014 1:32:07 PM
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We had medium (1KW) and high (10+KW) power HF transmitters in the Navy and the thrill of troubleshooting an open HV power supply drawer on a rolling ship brings back memories, not all fond! You learned early-on not to point at a suspected bad part, as the resulting arc could be painful and healed very slowly. Imagine working in a military radio transmitter site with 50 or so LF and HF transmitters all radiating between 1 and 100KW through exposed hard copper antenna leads stacked 9' above a sheet copper floor. You carried an insulated copper bar 6' long which had a trailing woven copper grounding strap that had a big alligator clip on the end; as long as the end of the copper bar was above your head, any stray RF would bleed to ground through the bar. Ball-lightening (loosely defined) was a common sight.

dj95014
User Rank
Iron
Neon lamps
dj95014   2/21/2014 3:50:52 PM
When I was in the Navy I worked onboard a carrier around a few high voltage circuits. However, I could never top one apocryphal story I heard from a Fire Control tech. He said that a shipmate went up into the island to trouble shoot a radar problem. The shipmate entered a compartment with his tool kit, set it down, opened it and discovered that all of his neon testers were glowing brightly. Whereupon he closed the kit and promptly left the area. I was told the the root cause turned out to be a hole in one of the waveguides.

William K.
User Rank
Platinum
Re: Neon lamps
William K.   4/4/2014 10:07:52 AM
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@dj95, I can easily believe that tale abot the neon tester lights, and am amazed that the person was able to leave with no injury. There are areas like that where one should simply never enter when the system is operating.

William K.
User Rank
Platinum
A very educational demonstration.
William K.   3/3/2014 3:38:45 PM
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Abord "some navy ship" (I don't wish to get in trouble for revealing excess information), one of our first things as new arrivals was a tour of the hazards to be found on board. One of those hazards was a radar antenna that was used for gathering details about things that other radar systems saw. We were cautioned to stay clear of the area on deck that had the painted warnings. The demonsration that convinced us was seeing seagulls fly into the beam and then hit the deck in a fairly cooked condition. Seeing was believing in that case.

Of course that was more high power than high voltage. The high voltage area for that system was also explained, as well as the hazards thereof. 

The other high voltage area was associated with some of the power system generators. The really nasty part of that hazard is that the high voltage had lots of amps behind it. So not only could it arc to a tool in your hand, it could then evaporate the tool. 

We were quite careful to stick to our assigned tasks and not visit elsewhere.

dgreig@ieee.org
User Rank
Iron
The Skin Effect
dgreig@ieee.org   4/2/2014 9:02:00 PM
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Whilst working with a well tanned Indian egnineer, on 5kV 200kHz resonant inverters and +-75kV transformers we both discovered the "skin effect" - a slight whitining of the epidermis when in close contact. My invertor design and was pleased that he added a rather graceful insight.

For me, and this was over 20 years ago, touching a 340VDC or 500VDC bus was a twice weekly event in the lab. Obviously no harm done! Being "Clyde Built" may have helped.

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