Appeared so, but we just tossed the whole thing in the trash, it was a mess.
I won't even mention the guy who destroyed a huge floorstanding Staco three phase Variac
that cost around $10k. That wheel on top is nearly a foot in diameter.
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Early in my career I worked on the RF side of broadcast TV. 200kw Transmitters with DEADLY voltages and current. The station group required any engineer on the RF side to attend a short electrical safety school. One comment from the instructor still hangs with me and it's quite good advice:
"Don't worry about contacting high voltage! Just don't allow yourself to become grounded. Where is your other hand? What are you standing on?"
When you think about it it's the ground that gets you, not the high voltage! Of course we are talking less than 25kv here. When you get up into the 100kv range, even air is a conductor.
"Don't worry about contacting high voltage! Just don't allow yourself to become grounded. Where is your other hand? What are you standing on?"
When you think about it it's the ground that gets you, not the high voltage! Of course we are talking less than 25kv here. When you get up into the 100kv range, even air is a conductor.
Of course we are talking less than 25kv here....Not really as my final years of doing tube colour TV work around 1978 when the final years of glass screens were quite wide there were other hazards such as radioactive cathodes in line output sections. 35kV wasn´t untypical. The old motto "keep the other hand in your pocket" is one that keeps me alive. Use probes with isolating clips one at a time as there´s no point getting stung by it as if it was a ranch fence. A good isolating transformer is also a prerequisite for the work we undertake with tube circuits.
That would suggest it is OK to touch high voltage as long as you keep one hand in your pocket. An irresponsible and possibly deadly suggestion.
ANY tech person worth his salt knows that it is the voltage across something, and across your body parts, that determines the current and the danger.
That is why multimeters have two leads.
Unless you levitate, you always have some contact with earth, so it is always dangerous to touch a live conductor.
One hand in the pocket may make the difference between death or 'only' a broken arm due to violent reaction, but only when you're lucky.
Just make sure it can't happen.
Jan
ANY tech person worth his salt knows that it is the voltage across something, and across your body parts, that determines the current and the danger.
That is why multimeters have two leads.
Unless you levitate, you always have some contact with earth, so it is always dangerous to touch a live conductor.
One hand in the pocket may make the difference between death or 'only' a broken arm due to violent reaction, but only when you're lucky.
Just make sure it can't happen.
Jan
Not quite correct. Keeping one hand in the pocket and standing on an insulated floor avoids any electric pulse around the critical body cardiac circuit. 1960´s Standard British TV trade practices.. It was even more dangerous remembering the those days of 240V AC/DC bakelite radios which was much worse with full mains current. Put the plug the wrong way round with a live chassis ? Ooop´s. Many of my colleagues fell for that one. Use an isolating transformer ! The same with HAM radio sets with exposed tank coils to catch the elbow, shocks then were common-place but more RF burns, which sting.
For those unfamiliar or new to this subject, worth a web peep at safety shoes and the industry definitions that constitutes EH (electrical hazard) designated footware. Loads of websites on this very issue. There are differences between secondary protection and elimination of static build up as regards resident resistances of both.
IMO it is the simplest things that catch most people out. Getting quickly out of my car does a "stinger bolt" every time. Does one learn ? The modern impulse cattle fence is another nasty that can get one´s parts right in the middle.
IMO it is the simplest things that catch most people out. Getting quickly out of my car does a "stinger bolt" every time. Does one learn ? The modern impulse cattle fence is another nasty that can get one´s parts right in the middle.
The “one hand in your pocket rule” keeps you from getting both hands across a live circuit. That path goes right through your heart. The path from your hand to your feet doesn’t. It can still kill, but the odds are a little better.
“Properly insulated“ floor spaces are a hazard for ESD. ESD won’t hurt a tube (unless we are talking lightning), but microcontroller boards and mosfets could get szhekxed. I’ve never blown out a TO-220 hexfet with ESD, but you are still supposed to handle them properly. With enough of a charge, you could build up 100 volts or more on the gate of even the biggest ones. Grounded bench, grounded floor, grounded operator, grounded tools - what is required in industry. That a B+ shock waiting to happen. A hobbyist tube-o-phile has to strike some sort of balance. Most of us “ignore” whatever ESD practices we can. And not everybody mixes modern digital stuff with their tubes - but some do.
“Properly insulated“ floor spaces are a hazard for ESD. ESD won’t hurt a tube (unless we are talking lightning), but microcontroller boards and mosfets could get szhekxed. I’ve never blown out a TO-220 hexfet with ESD, but you are still supposed to handle them properly. With enough of a charge, you could build up 100 volts or more on the gate of even the biggest ones. Grounded bench, grounded floor, grounded operator, grounded tools - what is required in industry. That a B+ shock waiting to happen. A hobbyist tube-o-phile has to strike some sort of balance. Most of us “ignore” whatever ESD practices we can. And not everybody mixes modern digital stuff with their tubes - but some do.
That's the difference between electronics and electrical.
No electrician with a working brain would ground themselves - they all wear electrically insulated PPE.
In reality, electricians working on high voltage will clip to the HV line and be at that voltage while they work (linesmen). They draw a long arc in the process.
No electrician with a working brain would ground themselves - they all wear electrically insulated PPE.
In reality, electricians working on high voltage will clip to the HV line and be at that voltage while they work (linesmen). They draw a long arc in the process.
Agreed, but there's a world of difference between the 25kv @ 1ma in a TV versus the 25kv @ 18amps in high power TV transmitters. Even 1kw ham transmitters are 3-5kv at several hundred milliamps.
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I was a Mr. Fixit at the Motorola plant in Florida from 1975 to 1984. During the 70's we made NiCad batteries and cells. There was a "very scary machine" for "polarizing" newly made NiCad cells that I got to fix several times. It included one of those huge three phase Variacs. That Variac fed a three phase custom made transformer that had three large copper bars sticking out of its side. There was a row of about 10 stud mounted diodes about the size of a doorknob on each bar. This apparatus made about 2 volts at "thousands of amps" which fed a rack of several hundred newly made NiCad cells. Measuring the current involved measuring the voltage drop across a piece of metal that was about a foot long and a half inch in diameter. When said "very scary machine" wouldn't make rated current, or blew the breaker, they called me, as the last guy managed to melt a large wrench and wouldn't go near the machine again. The line workers were quite astonished at my diagnostic technique. For blown breakers I turned the Variac up slowly until the scary machine emitted a loud hum and touched the fat braided cable coming out of each diode. The hot one would be on the shorted diode. For "won't make current" I turned the knob up full and again touched each wire. The cold one was on the open diode. Remember to turn off ALL the breakers before trying to change a diode. That machine was only scary to those who didn't understand it. All of the lethal voltage was enclosed inside the Variac box or the breaker panel. We did have other machines capable of killing a Mr. Fixit dead. They demanded respect and real safety procedures. The big CO2 lasers had power supplies rated for 25KV at half an amp. The vapor deposition chamber had a vacuum tube based RF "power supply" that ran on 3000 volts and made 1.5 KW of RF power.
The trick is that all the ESD mats, wristbands and such should have a 1 Meg resistor in the connecting lead, so that static bleeds off, but even contacting a 500V B+ is only 500uA (Which you will feel, but should not stick to).
You don't need much conductance to keep the static under control, and certainly do NOT need a hard ground connection.
O.M.O, 1 Meg for a bench mat is too low resistance. My bench mat has a 36 Megohm carbon resistor to main earth for static drain, and low voltage soldering iron 22M to mains ground........more than adequate. I am one of those who often work on circuits whilst they are active.....Only seasoned brazen veterans do this, unless I am totally wrong
. This year will have seen me 65 years of HV electronics.
Bear in mind, I get stung by more static for getting out of my car than I do from real shocks from my work bench !
. This year will have seen me 65 years of HV electronics.Bear in mind, I get stung by more static for getting out of my car than I do from real shocks from my work bench !
Yea, 1 Meg is a safety minimum, you can go way higher then that, and that is before you consider the resistance of the static dissipative sheet itself.
Point is that a correctly done ESD safe work area is just fine working around high voltage, there is no real conflict between an area where you can do cmos and one where tube work is safe.
Point is that a correctly done ESD safe work area is just fine working around high voltage, there is no real conflict between an area where you can do cmos and one where tube work is safe.
When I was a kid, my "O" level Physics teacher invited me to stand on a 3" thick block of expanded polystyrene and touch the (running) van der Graaf generator. I was mildly zapped. At the time, I thought it was deliberate* and teacher didn't like me. Which was a shame because I thought she was gorgeous. Decades later, I realised her physics knowledge wasn't great and that she had not considered the current required to charge my capacitance to the surroundings. Still, I learned that it's best not to touch live stuff. Even if you think you have taken precautions.
* Entirely normal teacher behaviour in those days. When Geography teacher threw a wooden board rubber at kid at the back of the class and got him on the side of the head, we were all impressed by the quality of her marksmanship.
EC8010.... I did go to UK schooling and Uni during the slide-rule time. When the geometry wasn´t correct, a green inkwell and soft chalk landed nearby (either way). The physics lab was potentially a very dangerous place with no sense of insulation or isolation transformer on bench work. It was quite normal for an early 405 line B/W TV using a radiation coated cathode to operate completely naked with a live chassis.
I find it interesting that all my recent test equipment exposed to 30V rms and above immediately flags a dangerous over voltage. An overkill as one might say. Although now in Germany one looks back to those high risk days, that in perspective today´s lot should have no excuse for getting electric jolts !
I find it interesting that all my recent test equipment exposed to 30V rms and above immediately flags a dangerous over voltage. An overkill as one might say. Although now in Germany one looks back to those high risk days, that in perspective today´s lot should have no excuse for getting electric jolts !
I've worked in crews laying residential Low Voltage where a common hazing was to get the new guy to test the POTS line with their tongue (a reasonably stiff 48VDC IIRC). Never in front of me, but it happened. One guy bought a two fixed prong taser and offered $100 to any of the crew who'd let him test it on them - fortunately no takers. I did much worse in my youth - guys are just dumb. Hold my beer!
All good fortune,
Chris
All good fortune,
Chris