Everything is dangerous if your scared of it.
Always keep one hand in your pockit
Thing I see is always start low and slow make sure you no where both hands are.

 

Exactly! Before they added all sorts of things to college ball. That's pretty cool with your dad. I never went to a bowl game but my parents lived in Worthington, north of campus and my dad would get OSU tickets. I made a few OSU home games.

My dad was on the faculty, and we always lived within walking distance of campus. I worked my way through school, EE during the day, nights building WOSU. I've missed a few home games.

 

I personally don't see the fear of working with AC. Guess it's because that's where I started with electrical things, AC. Or maybe you are still thinking about the Edison vs Tesla current war times? https://en.wikipedia.org/wiki/War_of_the_currents

Both can hurt you, but only if you do something stupid. You just need to play/work safe. If that wasn't the case we would all be living like the Amish.

The worst shock I ever got was from DC. It was from a discharge of a television tube. I was working late. Not paying enough attention when I tested for an arc under the HV cap of the tube. Either I forgot to ground the jumper or I became the ground. Either way I got zapped and knocked on my butt. I couldn't see for about 30 seconds. I still hate working with AC.

 

High voltage AC is safer than high voltage DC, but either can be bad. One "odd" shock I got years ago was after building a 100W tube audio amp. It was running 1Khz tone into a dummy load for some time as a test. I decided to see if the output transformer was heating, so put my hand on it to feel. But my fingers draped down and touched the anode top cap of one of the output valves. It bit!
Maybe you could argue it was DC with a large AC superimposed on it. Besides my exclamation, the arc produced had a 1Khz modulation that could be heard.
At least it was not a belt from one of the 100KW transmitters. If that was so, I would not be here to talk about it. 30KV DC supply with a working 5Amp capacity would not have been forgiving.
Still, the mains is the most common lethal power supply most people will come across so it does need to have safety stressed.
Mains shocks hurt! At least 240V ones do.

 

Late 60's, RCA color TV (the kind with the round CRT that was flattened across the top and bottom),. My thumb got between the boosted B+ and the chassis. But only for a very short time. It drilled a small, self-cauterized hole through the tip *and the nail*. I invented new words for that one. It was an excellent example of single-trial learning.

ak

 

Or so I have been warned. I saw a picture of one like this and wondered why. Something to do with not having an isolation xformer. Some variac do, but big $$$$. Price restricted.
I had planned to take the output of 3V to a breadboard someway and didnt see any bare wires laying around with more than 3V. So, where is it going to bite me ? Is it that there is a potential for the full mains voltage to be present on the case ?
And thanks, I didn't buy one but I want to know why.

View attachment 142563

Hi,

It is not the VOLTAGE SETTING that can hurt you, it is the fact that the output is always in contact with the line voltage which means you can get a shock even if you have it set to zero volts output if the ground wire of the line does not go to 0v on the variac input. This can happen if the outlet is not wired right or the plug is reversed in the outlet or the variac is not wired right, so it's tricky to get it right.

It is a little tricky to explain, but one lead of the line will always be connected to your circuit, and if that line lead happens to be the 'hot' side, you have 120vac on your circuit always even though it runs on only 3v ac.

To protect against shock, you can use an isolation transformer in addition to the variac.

If you are running a wall wart though, then the wall wart will provide isolation. It's only a risk when you use the variac output directly.

A variac will allow you to adjust the voltage output of some wall warts but not all. The non regulated type can be varied but the regulated type cant be varied.

 

Late 60's, RCA color TV (the kind with the round CRT that was flattened across the top and bottom),. My thumb got between the boosted B+ and the chassis. But only for a very short time. It drilled a small, self-cauterized hole through the tip *and the nail*. I invented new words for that one. It was an excellent example of single-trial learning.

ak

My first electronics job was a a test technician. One circuit hat a PCB mount pot with a disc to adjust it. It was convenient to put a finger on a nearby component to do the adjustment. I quickly (and permanently) learned not to use the transistor that had 90 volts on its case to steady my hand.

This was one of the _least_ scary/dangerous traps in the system I was testing. There was a CRT with plus and minus 2500 volts near it. This was at 60Hz so the rectified DC had huge filter caps.

 

I quickly (and permanently) learned not to use the transistor that had 90 volts on its case to steady my hand.

Those who do things, also make mistakes. Those who live after those mistakes develop deep respect for higher voltage.

Before i had HV probe, common practice was to hold CRT cap close to chassis and estimate voltage by length of spark. Scared and impressed everyone... until one day insulation had tiny crack near the CRT cap and i wanted to check what is this mad hissing all about. I was alone, unable to move for good few minutes, just trying to ignore buzzing in my ears, spinning room and focus on breathing.

tip of my index finger was burned. small puncture mark on skin was smoking and i was in serious pain. when i tried to rub it, it collapsed like deflated basketball. fortunately it recovered with time

 

Those who do things, also make mistakes. Those who live after those mistakes develop deep respect for higher voltage.

Before i had HV probe, common practice was to hold CRT cap close to chassis and estimate voltage by length of spark. Scared and impressed everyone... until one day insulation had tiny crack near the CRT cap and i wanted to check what is this mad hissing all about. I was alone, unable to move for good few minutes, just trying to ignore buzzing in my ears, spinning room and focus on breathing.

tip of my index finger was burned. small puncture mark on skin was smoking and i was in serious pain. when i tried to rub it, it collapsed like deflated basketball. fortunately it recovered with time

Hi,

Wow, sorry to hear that, must have been nasty.
I got shocked by maybe around 300vdc once in a basement. I was lucky to not get seriously injured. Maybe blanked out for a second or two that's all. Dont know if it had any long term effects though.
That was years and years and years ago when i was playing with tube amplifiers as that's all we had back then.

 

Variacs are no more dangerous than many of the things we encounter in day to day life. The trick, should we wish to call it a trick, id to understand the things around us that we use. Power tools are dangerous, yet many of us use them in our chosen line of work. Misuse of a variac can result in a nasty electrical shock but to just call a variac dangerous seems a bit foolish. High voltage transmission lines are dangerous yet they are maintained by people who know how to service them daily. Mains voltage is far from dangerous for those trained to work with and around it. Within electronics and electricity for the hobby enthusiast it was not always about low voltage DC and the wall wort. There was a time when projects were done around vacuum tubes (valves) which required DC power supplies of several hundred volts.

Working with electricity requires paying attention to detail and while there is no room for complacency when aware of what one is doing and working with electricity or an auto-transformer is hardly dangerous. I do not know anyone in the electrical / electronic field who has not been bitten (shocked). However, to say an auto-transformer is dangerous is just plain foolish unless we choose to say an auto-transformer is dangerous to an unskilled or untrained user who does not understand its operation.

Ron

 

Variacs are no more dangerous than many of the things we encounter in day to day life. The trick, should we wish to call it a trick, id to understand the things around us that we use. Power tools are dangerous, yet many of us use them in our chosen line of work. Misuse of a variac can result in a nasty electrical shock but to just call a variac dangerous seems a bit foolish. High voltage transmission lines are dangerous yet they are maintained by people who know how to service them daily. Mains voltage is far from dangerous for those trained to work with and around it. Within electronics and electricity for the hobby enthusiast it was not always about low voltage DC and the wall wort. There was a time when projects were done around vacuum tubes (valves) which required DC power supplies of several hundred volts.

Working with electricity requires paying attention to detail and while there is no room for complacency when aware of what one is doing and working with electricity or an auto-transformer is hardly dangerous. I do not know anyone in the electrical / electronic field who has not been bitten (shocked). However, to say an auto-transformer is dangerous is just plain foolish unless we choose to say an auto-transformer is dangerous to an unskilled or untrained user who does not understand its operation.

Ron

You are correct there but the TS was going to use a Variac to run 3VAC to a breadboard. THAT is potentially lethal. And not a very practical use of a Variac anyway.
As often happens, the original question was a bit lost along the way.

 

You are correct there but the TS was going to use a Variac to run 3VAC to a breadboard. THAT is potentially lethal. And not a very practical use of a Variac anyway.
As often happens, the original question was a bit lost along the way.

Oh I absolutely agree and as Analog pointed out good luck with repeatability as getting 3 volts on a standard US flavor 0 to 140 VAC is a trick unto itself.

Ron

 

I use the Variac to power a 120:12 transformer. That makes a low voltage output more like 25% rotation than 2.5% rotation of the knob on the Variac. Easier to adjust!

 

There's the answer.

 

Variacs are no more dangerous than many of the things we encounter in day to day life. The trick, should we wish to call it a trick, id to understand the things around us that we use. Power tools are dangerous, yet many of us use them in our chosen line of work. Misuse of a variac can result in a nasty electrical shock but to just call a variac dangerous seems a bit foolish. High voltage transmission lines are dangerous yet they are maintained by people who know how to service them daily. Mains voltage is far from dangerous for those trained to work with and around it. Within electronics and electricity for the hobby enthusiast it was not always about low voltage DC and the wall wort. There was a time when projects were done around vacuum tubes (valves) which required DC power supplies of several hundred volts.

Working with electricity requires paying attention to detail and while there is no room for complacency when aware of what one is doing and working with electricity or an auto-transformer is hardly dangerous. I do not know anyone in the electrical / electronic field who has not been bitten (shocked). However, to say an auto-transformer is dangerous is just plain foolish unless we choose to say an auto-transformer is dangerous to an unskilled or untrained user who does not understand its operation.

Ron

Hi again,

The reason we sometimes say a variac is dangerous is not because the variac in itself is dangerous it is the in situ common use where the expectation may be that of an isolated transformer. That is, an inexperienced user holds the belief that they are somehow getting isolation as well as a variable output. When that mistake is made, the variac becomes dangerous.

Somehow this belief that a variac is isolated came about over the years. I think it is because a transformer is usually isolated and it is more rare to find an auto transformer of fixed or variable voltage and when one is found it is sometimes just referred to as a transformer so the user may make the assumption that it's isolated too simply because it is a transformer and all the transformers they had encountered so far had been isolated.

So the danger really only comes in with the way it it used or in the way that it is believed that it can be used and that belief is all too common usually by people who are somewhat new to the field of electronics.

 

Hi again,

The reason we sometimes say a variac is dangerous is not because the variac in itself is dangerous it is the in situ common use where the expectation may be that of an isolated transformer. That is, an inexperienced user holds the belief that they are somehow getting isolation as well as a variable output. When that mistake is made, the variac becomes dangerous.

Somehow this belief that a variac is isolated came about over the years. I think it is because a transformer is usually isolated and it is more rare to find an auto transformer of fixed or variable voltage and when one is found it is sometimes just referred to as a transformer so the user may make the assumption that it's isolated too simply because it is a transformer and all the transformers they had encountered so far had been isolated.

So the danger really only comes in with the way it it used or in the way that it is believed that it can be used and that belief is all too common usually by people who are somewhat new to the field of electronics.

I wish I could click "Like" twice.

 

however, to say an auto-transformer is dangerous is just plain foolish unless we choose to say an auto-transformer is dangerous to an unskilled or untrained user who does not understand its operation.
Ron

And Ron, that describes me exactly. So, I am staying away from them for now.

 

You are correct there but the TS was going to use a Variac to run 3VAC to a breadboard. THAT is potentially lethal. And not a very practical use of a Variac anyway.
As often happens, the original question was a bit lost along the way.

Exactly right dendad. I started this thread based upon another thread.
What is still not so clear but not worth the effort to dig into it, is why couldn't they be made safer as a matter of course. $$$$, I am sure but there is more that I don't understand for another time.

 

Hi again,

The reason we sometimes say a variac is dangerous is not because the variac in itself is dangerous it is the in situ common use where the expectation may be that of an isolated transformer. That is, an inexperienced user holds the belief that they are somehow getting isolation as well as a variable output. When that mistake is made, the variac becomes dangerous.

Somehow this belief that a variac is isolated came about over the years. I think it is because a transformer is usually isolated and it is more rare to find an auto transformer of fixed or variable voltage and when one is found it is sometimes just referred to as a transformer so the user may make the assumption that it's isolated too simply because it is a transformer and all the transformers they had encountered so far had been isolated.

So the danger really only comes in with the way it it used or in the way that it is believed that it can be used and that belief is all too common usually by people who are somewhat new to the field of electronics.

My opinions are biased cause I work with mains voltage daily, and I've never had the benefit of an isolation transformer, but I would even go a step farther.

I would say that many people also over estimate the safety they get by using isolated transformers (which then feeds into the mistaken sense of security on non-isolating transformers.)

I know that the isolation is a huge safety benefit when you're stepping down to safe voltages, but I've heard countless people preach the importance of isolation transformers even when the output will still be potentially lethal. Don't get me wrong - I understand that isolation makes things a little safer, in that certain mistakes that could hurt you without isolation won't hurt you with isolation... but you're still dealing with lethal voltages, and you've still gotta have your head in the game and pay close attention or there are plenty of ways to get hurt even with isolation.

Maybe I'm misinterpreting people's statements and comments, but I get the distinct impression that some people feel a lot safer than they should when they use an isolation transformer.

If people didn't have so much faith in isolation transformers in the first place, there wouldn't be any confusion about non-isolated variac safety.

 

Exactly right dendad. I started this thread based upon another thread.
What is still not so clear but not worth the effort to dig into it, is why couldn't they be made safer as a matter of course. $$$$, I am sure but there is more that I don't understand for another time.

To make them safer would probably double their weight and price. I think if you just look at them as a variable mains supply that idea may help.
Don't connect anything to it that you would not just plug into the wall socket. A Variac is a really useful device, and I can't think of anything to easily replace them with to get the same functionality and power if you need variable mains power. Switched transformer tappings or a power amp running into a transformer could be used but the Variac is so much simpler and easy. But remember, it is an "Autotransformer", not a "normal" transformer.