Electronics for Audiophiles: Voltage and Current (Video)

[DonR]

Welcome to the forum (sincerely)!

But do stop furthering this bit of apocrypha about voltage being the primary risk in electrical injuries—I don’t know what is taught in engineering forums, but those of us in the medical field who deal with the consequences can assure you that although voltage does play a role in fatal outcomes from electrocution injuries, but current is the factor that correlates with morbidity and mortality.

Moderate to low voltages applied to low resistance tissues at high currents are lethal, while implantable defibrillators hit you with 6,000 volts at low currents for a fraction of a second and you’re A-OK.

Despite some debate about the worthiness of this topic for Amir’s primer, based on some of the answers I’ve seen here I’m concerned that quite a few folks might do well to go back to the basics on this one, or at least stop offering advice.

PS Your battery analogy was a poor one and a gross oversimplification of the science at work here. At this point I’m going to let this one go, because since you’re all still here, clearly you’re not putting yourself at substantial risks. But for the first time since I’ve been on this forum I’m the one speaking from a position of authority for a change, and folks are still convinced that their EE degrees grant them a medical license. I’m at the learned helplessness stage, you just can’t cut through the crap on here sometimes

We were taught the rule of thumb is 50V and up is unsafe and that while dry skin can handle a decent voltage, a sweaty palm or a wire puncturing the skin can lower the body's resistance by up to 2 orders of magnitude and all it takes is 25 mA or so to get through your heart to kill you. Not sure about anyone else but every time I am near high voltages, I sweat. I am glad that most of the high voltage power supplies I have used are current limited to 16 mA or less. Luckily, I think most of the time its a case of one hand touching a live wire and the circuit completing to ground so hopefully bypassing the heart through a fairly high resistance path. That is why we keep the other hand playing pocket pool.

 

[amirm]

I think its better to explain its the current trough the body that kills not the voltage.

No, no, no.

Once more, with high impedance of body, the only way to get sufficient current into body is to push the voltage up: I = V/R. You usually have no control or idea of current in the supply. But you know with very higher certainty the voltage. A 120 volt AC mains will absolutely cause more danger than 12 volt coming out an AC adapter. As a result, a person dealing with these situations only needs to look at the voltage to determine level of danger.

With respect to current, your worry is NOT electrical shock but short circuit sparks, fires, etc. I made this point clearly in the video as well.

I have built very high current Lithium battery cells. The worry there is always to make sure that you don't short them out (hence special attention to fusing, cabling, etc.). I never, ever worry about electric shock from such a 12 volt cell. And I don't know any other practicing tech or engineer that would either.

Your advice of worry about current in the context of electric shock is completely wrong and can lead to very dangerous advice to unskilled. I suggest leaving Internet arguments on this topic at the door. I explain what I explain in these videos based on real experience spanning decades (including many electric shocks) and proper fundamentals. Don't keep repeating these one-liners as if they have value. They do not.

 

[srkbear]

No, no, no.

Once more, with high impedance of body, the only way to get sufficient current into body is to push the voltage up: I = V/R. You usually have no control or idea of current in the supply. But you know with very higher certainty the voltage. A 120 volt AC mains will absolutely cause more danger than 12 volt coming out an AC adapter. As a result, a person dealing with these situations only needs to look at the voltage to determine level of danger.

With respect to current, your worry is NOT electrical shock but short circuit sparks, fires, etc. I made this point clearly in the video as well.

I have built very high current Lithium battery cells. The worry there is always to make sure that you don't short them out (hence special attention to fusing, cabling, etc.). I never, ever worry about electric shock from such a 12 volt cell. And I don't know any other practicing tech or engineer that would either.

Your advice of worry about current in the context of electric shock is completely wrong and can lead to very dangerous advice to unskilled. I suggest leaving Internet arguments on this topic at the door. I explain what I explain in these videos based on real experience spanning decades (including many electric shocks) and proper fundamentals. Don't keep repeating these one-liners as if they have value. They do not.

At this point I think I’d prefer to be wrong and happy. Obviously “Danger—High Voltage!” is the appropriate nincompoop warning to keep dolts safe from jolts, because the average Joe is most likely in general to run into trouble if they mess with electrons under considerable force.

As for the actual science involved in electrical injuries, my training and experience and rounds in burn units for two decades be damned—it’s your forum, and I’ll defer to your omniscience.

One thing I do want to clarify though, with no rejoinder expected—the impedance of the contact surfaces of the human body ranges from 300 ohms all the way up to 100,000, depending on surface area, region, moisture, and integrity of the tissue involved. If a live source punctures the epidermis, the body’s impedance can actually drop quite low. And for what it’s worth, I did enjoy your video. Peace.

 

[amirm]

One thing I do want to clarify though, with no rejoinder expected—the impedance of the contact surfaces of the human body ranges from 300 ohms all the way up to 100,000, depending on surface area, region, moisture, and integrity of the tissue involved. If a live source punctures the epidermis, the body’s impedance can actually drop quite low. And for what it’s worth, I did enjoy your video. Peace.

Typical person messing with audio is indoors, usually on dry, insulated flooring and surroundings. So issues like moisture and such, don't enter the equation. Indeed, chances of electrocution in such situations is extremely rare as there would be many dead electronic technicians! Industrial or outdoor work is entirely different situation.

As I explained, the factors you mention are not what a person can determine anyway. As such, they are best to stay away from high voltage which I defined as low as 30 volts. Keep in mind that your speaker terminals generate this type of voltage. How many audiophiles you know that have been shocked by that?

I repeat again: any talk about current being more lethal than voltage will lead to opposite and dangerous advice to audiophiles.

 

[srkbear]

Typical person messing with audio is indoors, usually on dry, insulated flooring and surroundings. So issues like moisture and such, don't enter the equation. Indeed, chances of electrocution in such situations is extremely rare as there would be many dead electronic technicians! Industrial or outdoor work is entirely different situation.

As I explained, the factors you mention are not what a person can determine anyway. As such, they are best to stay away from high voltage which I defined as low as 30 volts. Keep in mind that your speaker terminals generate this type of voltage. How many audiophiles you know that have been shocked by that?

I repeat again: any talk about current being more lethal than voltage will lead to opposite and dangerous advice to audiophiles.

They’re both lethal, Amir, clearly. I never said voltage wasn’t important or dangerous. I believe it was you who responded to the omission of this topic in the video by defining your audience as above a remedial level, and what I offered was in that spirit. We all know Ohm’s Law, and it’s clear you can’t have an electrical injury without a combination of both factors. However I see electrical injuries and burns from all causes, not just from capacitors and wires and batteries.

And since this is a scientific forum, I was endeavoring, perhaps hoping—for once—to offer insight on a topic for which I had specific expertise—in the humble service of enlightening others on here for a change, as I am otherwise a lay person amongst engineers. I realized that it was a tall order, because as much as I admire you and benefit from your startling fund of knowledge about innumerable disciplines in general but my favorite hobby in particular, I have to timidly admit that I have not known you to admit you’re wrong all that much or to apologize easily. So if it won’t steal too much of your sunshine at 1AM on a Tuesday, I’ll offer the following, just in case someone might be interested…

From our gold standard text on electrical injuries:

“Injuries due to electricity occur by three mechanisms:

●Direct effect of electrical current on body tissues

●Conversion of electrical energy to thermal energy, resulting in deep and superficial burns

●Blunt mechanical injury from lightning strike, muscle contraction, or as a complication of a fall after electrocution

The primary determinant of injury is the amount of current flowing through the body. Clinically, contact with a 120 V circuit carrying a 1 milliampere (mA) current is imperceptible to most persons, 3 mA leads to mild tingling, and 10 to 12 mA leads to pain. One hundred mA directed across the heart can cause ventricular fibrillation. In addition, the voltage, resistance, type of current (AC or DC), the current pathway, and duration of contact all influence the extent of injury.

The tissue damage inflicted by most electrical currents can be primarily attributed to the thermal energy (or heat) generated by the current, as predicted by Joule's law:

Heat = current (I) x voltage (V) x time of contact (t)

= I x V x t
= I x (I x R) x t (from Ohm's Law)
= I2 x R x t

Resistance is a function of the area of contact, pressure applied, and the presence of moisture. Tissues with higher resistance have a tendency to heat up and coagulate, rather than transmit current. Skin, bone, and fat have high resistances, while nerves and blood vessels have lower resistances.

Of all organ systems, the skin has the greatest effect on the severity of an electrical injury. Dry skin has a resistance of approximately 100,000 ohms; however, this drops to less than 2500 ohms when the skin is dampened. Thus, in some cases, a lower voltage applied to tissue with low resistance can generate more current and be more damaging than higher voltage applied to tissue with high resistance.

DC current tends to cause a single muscle spasm that throws the victim from the source. This results in a shorter duration of exposure, but a higher likelihood of associated trauma. In contrast, AC repetitively stimulates muscle contraction. Often, the site of exposure is at the hand, and because the flexors of the arm are stronger than the extensors, the victim may actually grasp the source, prolonging the duration of contact and perpetuating tissue injury.

The amount of AC needed to cause injury varies in proportion to its frequency, expressed in cycles per second or hertz (Hz). Skeletal muscle can become tetanic with frequencies between 15 and 150 Hz, and although a 20 mA current may not be perceptible at 10 Hz, the same current may cause respiratory paralysis or ventricular fibrillation at lower frequencies.”

Thanks for allowing me the floor for a brief moment Amir, truly. I’m done, back to you.

 

[DualTriode]

No, no, no.

Once more, with high impedance of body, the only way to get sufficient current into body is to push the voltage up: I = V/R. You usually have no control or idea of current in the supply. But you know with very higher certainty the voltage. A 120 volt AC mains will absolutely cause more danger than 12 volt coming out an AC adapter. As a result, a person dealing with these situations only needs to look at the voltage to determine level of danger.

With respect to current, your worry is NOT electrical shock but short circuit sparks, fires, etc. I made this point clearly in the video as well.

I have built very high current Lithium battery cells. The worry there is always to make sure that you don't short them out (hence special attention to fusing, cabling, etc.). I never, ever worry about electric shock from such a 12 volt cell. And I don't know any other practicing tech or engineer that would either.

Your advice of worry about current in the context of electric shock is completely wrong and can lead to very dangerous advice to unskilled. I suggest leaving Internet arguments on this topic at the door. I explain what I explain in these videos based on real experience spanning decades (including many electric shocks) and proper fundamentals. Don't keep repeating these one-liners as if they have value. They do not.

@amirm,

Sorry to report that you are completely mistaken.

For more than a few years I have made my living in hospitals, operating rooms, procedure rooms and medical research facilities. For ten years plus I worked at University of California teaching hospital with 25 plus operating rooms, one with a MRI scanner in the O.R. After that I was a consulting engineer for a M.E.P. engineering firm that specializes in health care facilities.

Every hospital approved by the JCAHO to receive Medicare money is designed, inspected and tested to compliant to NFPA 70, NFPA 99 and NFPA 101. Without JCAH approval the insurance companies will not pay for services in a unlicensed facility That is just a beginning.

Medical electrical device are also designed and tested to be compliant to NFPA standards.

Now take the time to look up the Life Safety Codes, they are all about limiting current through the human body if your body is the unfortunate path to ground.

Part of the acceptance testing does measure differential voltage between grounded surfaces in the O.R. The intention is to stop even uA levels of current flow.

Thanks DT

Just a sample

https://www.controlledpwr.com/wp-content/uploads/2018/07/NFPA-99-Compliant-UPS.pdf

 

[amirm]

They’re both lethal, Amir, clearly.

They are not both lethal. Saying this means touching the battery terminals in your car shocks you. Tell that to any mechanic and they would think you are from Mars.

No way can you quantify "dangerous current" in any audio equipment. You can however easily quantify dangerous voltage.

Go ahead and tell me what the implications are for an audiophile in what you wrote. What is safe for them to touch and what is not? This was the one and only point of that one line in the presentation was.

 

[amirm]

@amirm,

Sorry to report that you are completely mistaken.

For more than a few years I have made my living in hospitals, operating rooms, procedure rooms and medical research facilities. For ten years plus I worked at University of California teaching hospital with 25 plus operating rooms, one with a MRI scanner in the O.R. After that I was a consulting engineer for a M.E.P. engineering firm that specializes in health care facilities.

Every hospital approved by the JCAHO to receive Medicare money is designed, inspected and tested to compliant to NFPA 70, NFPA 99 and NFPA 101. Without JCAH approval the insurance companies will not pay for services in a unlicensed facility That is just a beginning.

Medical electrical device are also designed and tested to be compliant to NFPA standards.

Now take the time to look up the Life Safety Codes, they are all about limiting current through the human body if your body is the unfortunate path to ground.

Part of the acceptance testing does measure differential voltage between grounded surfaces in the O.R. The intention is to stop even uA levels of current flow.

Thanks DT

Clearly you have lost the plot. None of this has remotely anything to do with the topic of my comment in the video. Someone touching a piece of equipment simply needs to know what is dangerous, and what is not per my last post. This has nothing to do whatsoever with safety standards for equipment design, the code, etc.

And are you kidding me with that line about insurance companies? You think an audiophile's home is covered as "unlicensed facility?"

 

[srkbear]

They are not both lethal. Saying this means touching the battery terminals in your car shocks you. Tell that to any mechanic and they would think you are from Mars.

No way can you quantify "dangerous current" in any audio equipment. You can however easily quantify dangerous voltage.

Go ahead and tell me what the implications are for an audiophile in what you wrote. What is safe for them to touch and what is not? This was the one and only point of that one line in the presentation was.

I meant they work together, I never said they are both lethal, and I have no idea why you are being so inexplicably defensive and contentious about this. I am looking at this topic from a completely different perspective than you are, based on our different disciplines.

And since you’re at risk of, and experienced with, one comparably tiny proportion of all the cases I’ve seen involving electricity and the human body in my career, and since I have 15 years of training at a leading university medical center and another ten teaching there, I’m wondering what threshold of credibility is required—if any—for you to not lecture someone who in one tiny sliver of space on this forum, has greater authority than you on a single subject. Are you really that authoritarian and undiplomatic in your views? What is wrong with you?

 

[srkbear]

Clearly you have lost the plot. None of this has remotely anything to do with the topic of my comment in the video. Someone touching a piece of equipment simply needs to know what is dangerous, and what is not per my last post. This has nothing to do whatsoever with safety standards for equipment design, the code, etc.

And are you kidding me with that line about insurance companies? You think an audiophile's home is covered as "unlicensed facility?"

Now I just think you’re being an insufferable jerk. This isn’t a collegial conversation. I’m shocked by your lack of humility on this one Amir, you have my utmost respect but this I don’t understand at all. Goodnight.

 

[amirm]

I meant they work together, I never said they are both lethal, and I have no idea why you are being so inexplicably defensive and contentious about this. I am looking at this topic from a completely different perspective than you are, based on our different disciplines.

And since you’re at risk of, and experienced with, one comparably tiny proportion of all the cases I’ve seen involving electricity and the human body in my career, and since I have 15 years of training at a leading university medical center and another ten teaching there, I’m wondering what threshold of credibility is required—if any—for you to not lecture someone who in one tiny sliver of space on this forum, has greater authority than you on a single subject. Are you really that authoritarian and undiplomatic in your views? What is wrong with you?

This is as serious of a topic as it gets: what is safe to play with in electronics and what is not. I asked you this question and you refused to answer. I provided the answer that anyone working in electronics day in and day out knows and follows in the video. Nothing about this is related to treatment of such in which you have expertise.

My presentation here was specific for audiophiles and meant to inform them of key concepts they need to learn. And that key concept is mains is dangerous, low output DC from a power supply is not. Anything else you want thrown in there muddies this clear message and can lead to confusion and hence danger.

 

[DualTriode]

Clearly you have lost the plot. None of this has remotely anything to do with the topic of my comment in the video. Someone touching a piece of equipment simply needs to know what is dangerous, and what is not per my last post. This has nothing to do whatsoever with safety standards for equipment design, the code, etc.

And are you kidding me with that line about insurance companies? You think an audiophile's home is covered as "unlicensed facility?"

No we do not need to follow the National Electric Code when we do stuff on out bench. However we do spend a lot of time discussing UL listings and other certifications that the Codes require.

The only reason that I brought up the safety codes is that the codes identify the hazard.

The hazard is current.

DT

 

[amirm]

Now I just think you’re being an insufferable jerk. This isn’t a collegial conversation. I’m shocked by your lack of humility on this one Amir, you have my utmost respect but this I don’t understand at all. Goodnight.

Watch your language. I am confident you didn't understand a word in his post so I suggest, you keep your cool and not interject.

 

[tomtoo]

No, no, no.

Once more, with high impedance of body, the only way to get sufficient current into body is to push the voltage up: I = V/R. You usually have no control or idea of current in the supply. But you know with very higher certainty the voltage. A 120 volt AC mains will absolutely cause more danger than 12 volt coming out an AC adapter. As a result, a person dealing with these situations only needs to look at the voltage to determine level of danger.

With respect to current, your worry is NOT electrical shock but short circuit sparks, fires, etc. I made this point clearly in the video as well.

I have built very high current Lithium battery cells. The worry there is always to make sure that you don't short them out (hence special attention to fusing, cabling, etc.). I never, ever worry about electric shock from such a 12 volt cell. And I don't know any other practicing tech or engineer that would either.

Your advice of worry about current in the context of electric shock is completely wrong and can lead to very dangerous advice to unskilled. I suggest leaving Internet arguments on this topic at the door. I explain what I explain in these videos based on real experience spanning decades (including many electric shocks) and proper fundamentals. Don't keep repeating these one-liners as if they have value. They do not.

Amir i completly get you. You like to keep it easy. Imo to easy. No voltage will kill me as long no current runs thru my body or the current is not high enough . And thats how it is. You like to explain it from a practical point of view to the average joe, ok. But this not tells the real story. To tell the complete story, you have to talk about resistance. You have to talk about body resistance and inner resistance of a voltage source. Yes more complicated, but people that see this as to complicated should just not "bastel" on electrical devices.

 

[amirm]

No we do not need to follow the National Electric Code when we do stuff on out bench. However we do spend a lot of time discussing UL listings and other certifications that the Codes require.

The only reason that I brought up the safety codes is that the codes identify the hazard.

The hazard is current.

DT

You can throw away all of that as soon as you open a piece of equipment. There is not a shred of regulation that applies to that situation. And per my repeated post, any mention of "current being the hazard" is totally wrong with respect to what is and is not dangerous inside some audio gear.

But I will humor you. Go ahead and explain what you can, or cannot touch given your claim that "hazard is the current." This is the second time I am asking.

 

[srkbear]

This is as serious of a topic as it gets: what is safe to play with in electronics and what is not. I asked you this question and you refused to answer. I provided the answer that anyone working in electronics day in and day out knows and follows in the video. Nothing about this is related to treatment of such in which you have expertise.

My presentation here was specific for audiophiles and meant to inform them of key concepts they need to learn. And that key concept is mains is dangerous, low output DC from a power supply is not. Anything else you want thrown in there muddies this clear message and can lead to confusion and hence danger.

This is the last I think I should say on this because no communication is happening here, but I’ll remind you that this imminently life threatening and catastrophic issue you’re invoking now is the same one you initially declared was too remedial and unnecessary for you to include in your video—when challenged on it by one well-meaning person amidst the rally of adulation and high-fives you’re accustomed to.

Throughout this entire discussion your audience has been engaging in a perfectly safe, stimulating discussion on this topic, and your only contributions have been to argue and denigrate those posts where you found opportunity to do so. I think you’re demonstrating intolerance of any criticism, silencing or shaming those who differ in your opinion, and what I’m making up—charitably—is that basically you worked very hard on this video, and had very clearly defined expectations of the response.

In my experience with scientific inquiry and academia, when I present a lecture on a particular subject of interest to me, the questions, challenges and criticisms are the most enjoyable, stimulating and informative aspects of the endeavor. To feel this way one has to proceed with the belief that one’s fund of knowledge is not complete.

I wish you had handled this differently, but as I said I enjoyed your video, and look forward to more of them. In the future I’ll keep my comments within the strict sphere of those topics solely of interest/use to the audiophile, and I’ll be mindful not to encroach upon your place on the lectern. Good night.

 

[srkbear]

Watch your language. I am confident you didn't understand a word in his post so I suggest, you keep your cool and not interject.

I understood him fine! I’m an associate professor of medicine, if you landed in an ER I’d care for you—please do not talk to me that way. I’m being civil here, and I don’t think you’re being kind. I’m prepared to shake hands and walk away peacefully from this—but please don’t talk to me that way anymore. I made a considerable donation to support your efforts—at minimum please don’t insult my life’s work. I may have disagreed with you on this topic but I’ve repeatedly praised your work.

 

[amirm]

I understood him fine! I’m an associate professor of medicine, if you landed in an ER I’d care for you—please do not talk to me that way. I’m being civil here, and I don’t think you’re being kind. I’m prepared to shake hands and walk away peacefully from this—but please don’t talk to me that way anymore. I made a considerable donation to support your efforts—at minimum please don’t insult my life’s work. I may have disagreed with you on this topic but I’ve repeatedly praised your work.

Oh? You know the NEC? How about "NFPA 70, NFPA 99 and NFPA 101?" The insurance code? The teach you these things in med school? I think not.

Come work for me as an electronic tech and I will teach you how to stay alive. If you violate that and listen to internet arguments about "it is current that kills you," then sadly your odds of needing the services from someone like you rises substantially.

 

[solderdude]

It is really simpele.
You have tot watch out for high voltages.
That is...... high voltages that van provide a lethal current.
Such are
1. mains ( ground referenced, which most is)
2. High AC and DC voltage rails inside (mostly tube Gear) which has voltages referenced tot (audio)ground.
Touching low voltage rails, unless one came from the shower, punctured the skin on a sharp pin while standing barefoot on a somewhat conductive floor from grounded mains fed audio gear is niet going tot kill you as not enough current can/will flow.

So watch out for high er voltages in general is sound advice. A high voltages acties the body van easily lead tot high enough currents that van potentially kill domeinen.

One has to creatie a current path as well going either to the floor (through the body) or from hand to hand, so one hand on the metal chassis and the other hand touching the exposed voltage.
When that path exists a lethal current can flow.

I have accidentally touched 220V mains, got jolted by 1.5kV between electrostat stators, high voltages in CRT and SMPS by being careless and lived to tell with only some small burns here and there.

 

[pma]

Guys, this debate is ridiculous and reminds me to a story what was the first: the hen, or the egg?

Every oversimplification is wrong, and actually we have some standards to define safe voltage and safe current, under various conditions.