I just read this entire thread from beginning to end and I'm glad that I did. As the result, when I move into my new house, I'll put a rubber mat under my workbench and the area directly in front of it. The work bench will be in the laundry room. There is a ceramic tile floor over concrete, and I know that high voltage can go through concrete if there is even a trace of moisture. It might also be able to go through the tile grout. Also, I shall get an isolation transformer.
As it turns out, I am usually unable even to feel 120 volts, but with voltages possibly exceeding 300 volts, there is a high risk. Years ago, when I took a course in industrial electronics, someone connected a plug to 120 vac and in series with an milliammeter and had me hold the plug between thumb and forefinger. I was able to hold it for about 30 seconds as the current gradually increased, then I had to drop it. But, high voltages are a different matter.
In the 19th century, it was discovered that AC is more dangerous than DC. Edison used that information in an unsuccessful attempt to promote his DC systems. Westinghouse pushed AC. Edison, to scare people, wanted electrocution to be called Westinghousing, so that people would be Westinghoused in electric chairs. He was a bit eccentric.
The GFIs here are supposed to trip at only 6 ma and are ordinarily built into receptacles. However, in Fiji (I lived there for 10 years) and Australia, the GFIs (they call them earth leakage breakers) are normally in the power panel and, to prevent nuisance tripping resulting from leakage, trip at a much higher current (about 20 ma, if I correctly recall). To make things even worse, the same ELB is used for several circuits by feeding multiple circuit breakers. If you ever go to a country which uses only 240 volts, remember that black is earth and white is "active."
As it turns out, I am usually unable even to feel 120 volts, but with voltages possibly exceeding 300 volts, there is a high risk. Years ago, when I took a course in industrial electronics, someone connected a plug to 120 vac and in series with an milliammeter and had me hold the plug between thumb and forefinger. I was able to hold it for about 30 seconds as the current gradually increased, then I had to drop it. But, high voltages are a different matter.
In the 19th century, it was discovered that AC is more dangerous than DC. Edison used that information in an unsuccessful attempt to promote his DC systems. Westinghouse pushed AC. Edison, to scare people, wanted electrocution to be called Westinghousing, so that people would be Westinghoused in electric chairs. He was a bit eccentric.
The GFIs here are supposed to trip at only 6 ma and are ordinarily built into receptacles. However, in Fiji (I lived there for 10 years) and Australia, the GFIs (they call them earth leakage breakers) are normally in the power panel and, to prevent nuisance tripping resulting from leakage, trip at a much higher current (about 20 ma, if I correctly recall). To make things even worse, the same ELB is used for several circuits by feeding multiple circuit breakers. If you ever go to a country which uses only 240 volts, remember that black is earth and white is "active."
FRE; this has its drawbacks too. CMOS is easily destroyed... by being safe for oneself as an insulator stores static. You are on the right track, but the solution is to find an anti static mat which can deal with both problems.
PS; The Ford motor company still hasn't learnt to use anti static upholstery that doesn't give me a darned jolt when getting out of my car. Maybe blame my clothes.
richy
PS; The Ford motor company still hasn't learnt to use anti static upholstery that doesn't give me a darned jolt when getting out of my car. Maybe blame my clothes.
richy
To make it clear
In the US:
Live/hot = Black
Neutral/cold = White
Earth (if used) = Green
Current International (CENELEC):
Yellow+Green: Safety ground
Blue: Neutral
Brown: First phase conductor
Black: Second phase conductor
Gray: Third phase conductor
but the old international colours were:
Live = Red
Neutral = Black
Earth = Green
So a serious mistake can be made if you confuse the US active/phase black wire with an old international neutral black wire. This can happen when you are working on an older piece of equipment
So the correct answer is ALWAYS check your wiring with a meter BEFORE applying power. Even if you have the correct colours, the 'other guy' might have mis-wired the conections - because YOU would never make a mistake would you?
richwalters said:
That's especially true here in Albuquerque where the relative humidity is usually the same as in desserts. One of the advantages of vacuum tubes is that, unlike solid state devices, they are insensitive to static discharges (and nuclear radiation). For working with solid state devices, conductive wrist bands with wires are available; one clips the attached wire to a ground. Those are fine for low voltages, but I wouldn't want to use one where voltages may exceed 300 volts.
Regarding staticky upholstery in cars, way back in the 1950s people used to install plastic seat covers. In dry weather, one always got a shock after sliding across the (bench type) seat and touching the door handle. In those days, car radios had vacuum tubes; a vibrator, transformer, and Hg vapor rectifier generated the high emf. When I had my antique Packards, I 'phoned around to various auto supply places trying to find vibrators. Later I realized that they were probably unfamiliar with vacuum tube radios and thought that I had a different kind of vibrator in mind.
For workbenches, try the 3M Ultra R2 rubber table mats. P/N RM2436L2RBL is one example
These are ESD safe but have a high enough resistance for electrical safety.
Ultra r2 Rubber Table Mat
I've used one for a number of years.
These are ESD safe but have a high enough resistance for electrical safety.
Ultra r2 Rubber Table Mat
I've used one for a number of years.
VivaVee said:
There must be mats available for computer rooms. If so, they would probably work.
Years ago, when I worked for Data 100 in suburban Minneapolis, I found what static electricity could do to a computer. I walked across the room and touched the computer. Immediately, it halted on a memory parity error, the printer ejected a page, and the card punch (remember those?) ejected a card. Fortunately, no damage was done, but after that, I always removed my shoes upon entering the computer room.
Id like to add an experience I had, if i may..
Last week I powered up my first ever build for the first time, very exciting!
The plan was to test the output of the rectifier so I new how much I had to bring the voltage down for my circuit. Everything was checked and double checked and I turned it on. However there was no reading on the multimeter. My lecturer and I decided to turn it off and check all stages one more time.
So I turned it off, put my hands on the leads to the DVM and got quite a shock.
The DVM AC/DC switch turned out to be faulty and I was trying to read a DC signal in AC. With a new DVM it showed that the rectifier was in fact producing 356V DC.
I can only assume that the rubber soles on my trainers, or just sheer luck is the reason I am still here. It was certainly a wake up call, and I have a new found respect for electricity.
All I can say is check everything twice, and then twice again. Not everyone will be as lucky as me...
Charlie
Last week I powered up my first ever build for the first time, very exciting!
The plan was to test the output of the rectifier so I new how much I had to bring the voltage down for my circuit. Everything was checked and double checked and I turned it on. However there was no reading on the multimeter. My lecturer and I decided to turn it off and check all stages one more time.
So I turned it off, put my hands on the leads to the DVM and got quite a shock.
The DVM AC/DC switch turned out to be faulty and I was trying to read a DC signal in AC. With a new DVM it showed that the rectifier was in fact producing 356V DC.
I can only assume that the rubber soles on my trainers, or just sheer luck is the reason I am still here. It was certainly a wake up call, and I have a new found respect for electricity.
All I can say is check everything twice, and then twice again. Not everyone will be as lucky as me...
Charlie
There are probes available that clamp on to the terminals to be tested. I haven't used one myself, but probably they are a good idea. They could be connected before powering up the device. Surely they would enhance safety by making it easier to use only one hand, or to use no hands. Also, they would reduce the liklihood of having a probe slip and cause a short curcuit.
When building, it might be a good idea to take clamp-on probes into consideration by shaping connections to expedite using clamp-on probes.
When building, it might be a good idea to take clamp-on probes into consideration by shaping connections to expedite using clamp-on probes.
Don't rely on isolation transformers or GFI's to protect you from voltages over 1000! At those potentials, a lethal current can be passed through you without tripping the GFI, popping circuit breakers or blowing fuses.
All the rules and tips posted here are good; but the number one rule in my book is to use CARE and pay attention to what you're doing.
The one time I got zapped by HV - about 50 years ago when I was a young ham working on a HV power supply - it was because I got careless (and forgot to discharge the filter caps). Luckily I was sitting in a swivel chair on wheels and the muscle reaction from my forearms which were in contact with the bench shot me backwards to the far wall - where I ended up with a nice knot on my head where it hit the wall to go along with the tingling sensation in my arm from the shock! ...Never again!
Be careful out there...
Bud
All the rules and tips posted here are good; but the number one rule in my book is to use CARE and pay attention to what you're doing.
The one time I got zapped by HV - about 50 years ago when I was a young ham working on a HV power supply - it was because I got careless (and forgot to discharge the filter caps). Luckily I was sitting in a swivel chair on wheels and the muscle reaction from my forearms which were in contact with the bench shot me backwards to the far wall - where I ended up with a nice knot on my head where it hit the wall to go along with the tingling sensation in my arm from the shock! ...Never again!
Be careful out there...
Bud
If it is less than 1000 volts...then I'm not interested!!! Trained on radar and radiotelephone equipment in the Air Force. No jewlery, one hand rule lock out tag out, etc. Still working on high voltage going on over three decades in the private sector.(digital WAS a fad all those jobs are in China)
I'll add that no matter what the voltage, after replacing components in anything, find a way to make sure all your little clipped leads, wire strands, and solder drippings ALL come out before you power up.
Use a brush, compressed air, something... along with a bright light, and make sure none of your "debris" is going to fall free, now, or in the future, and land across a couple dangerous places.
Regards...
art
Use a brush, compressed air, something... along with a bright light, and make sure none of your "debris" is going to fall free, now, or in the future, and land across a couple dangerous places.
Regards...
art
I actually had a transistor amplifier (a 50 wpc Pioneer SX838) that kept a 40V charge in each of the big capacitors (80V total) for days.
Days. Fully assembled and working, obviously when off there was no current path, even via the main output transistors.
I added bleeder resistors after I discovered that!!
Days. Fully assembled and working, obviously when off there was no current path, even via the main output transistors.
I added bleeder resistors after I discovered that!!
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Very helpful thread. I'm about to start on my first tube amp and this are good precautions. I hope I've captured them all. What I have taken away from this thread is:
Safety - preparing the Environment:
a) use a well lit workspace
b) insulated floor surface (rubber mat preferred, dry newspapers for 'plan B') and wear sneakers
c) mains isolation transformer is recommended
d) fit bleeder resistors to all hv capacitors - there's no need to ever remove them
Safety - preparing for work
a) make sure you are not working alone
b) double check everything, e.g. no foreign parts stuck in the chasis, insulation on hv parts, earth straps secure
c) if feeling tired, stop
d) before plugging in the power check isolation between chasis and prongs on power plug using ohm meter (chasis to power should be at least 1M)
e) after plugging in the power, before flicking the switch, put one hand in pocket
f) don't 'drink and drive' with hv
Safety - working with powered chasis
a) don't take the hand out of your pocket !
b) work methodically without haste
c) stop if feeling tired
Safety - finishing work
a) after turning off power wait and confirm psu caps are discharged before leaving the work area
b) physically disconnect the power
c) take hand out of pocket !
Yikes !
Safety - preparing the Environment:
a) use a well lit workspace
b) insulated floor surface (rubber mat preferred, dry newspapers for 'plan B') and wear sneakers
c) mains isolation transformer is recommended
d) fit bleeder resistors to all hv capacitors - there's no need to ever remove them
Safety - preparing for work
a) make sure you are not working alone
b) double check everything, e.g. no foreign parts stuck in the chasis, insulation on hv parts, earth straps secure
c) if feeling tired, stop
d) before plugging in the power check isolation between chasis and prongs on power plug using ohm meter (chasis to power should be at least 1M)
e) after plugging in the power, before flicking the switch, put one hand in pocket
f) don't 'drink and drive' with hv
Safety - working with powered chasis
a) don't take the hand out of your pocket !
b) work methodically without haste
c) stop if feeling tired
Safety - finishing work
a) after turning off power wait and confirm psu caps are discharged before leaving the work area
b) physically disconnect the power
c) take hand out of pocket !
Yikes !
I had a microphone phantom power circuit that in the haste of constructing to a deadline I forgot to put bleed resistors in; I found the caps still had 35V(out of about 50) after nearly two months. I think this must be an extreme case. They were described as computer grade electrolytics and were 6800 uF.
For all new to tubes!
So when you are working on or building a project.
Please ensure you fit discharge resistors to your project!
A good safety feature is to fit a 1M ohm 2-3Watt across your HT supply it will give a slow discharge should you have a break and start work on your project assuming you have discharged your HT! It may save you!
The golden rule test before you touch!
Those that already know take precautions!
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I know little about electronics. More about cars. Automotive ignition systems used to build around 15,000 to 20,000 volts. Today, 30,000-volt systems are wimpy. 40K-50K-60K and beyond are common. This amount of voltage is just ITCHING to go to ground. It will find the craziest paths. I have personally seen 3" arcs. I have also personally become a conductor, and this voltage will get your attention. Never ever touch an ignition distributor cap or ignition wires while the engine is running.