60V DC dangerous?

EDN magazine had an article in the May 11 issue on the subject. You can get to it online at:

Regards, Mike Stanley

Mike M>

Piffle. Only 1A. That is nothing.

For entertainment and pleasure, some reach for a Bud.

Real men grab 16,600 Volts!

Officially hazardous with some risk of shock being able to be fatal.

DC, at least smmoth DC, is less likely to cause death than AC of frequency in/near the 50/60 Hz ballpark. By-and-large, DC has some significant hazard down to about 50 volts and AC down to about 25-30. Less if you are likely to be wet with sea water - then, 28 volts DC is borderline (29 volts is "officially hazardous") and AC is no better down to something lower - maybe 13-15 volts?

Keep in mind that the horror stories of DC causing bad burns in railroad/subway workers got told by people who survived and lived to tell the ugly tales of top degree burns extending into deep tissue and muscles and burn damage can have a halflife of 7 years or whatever and muscles with fibers being totalled will never be the same again and nerves grow back at some awfully slow pace or even worse when nerve cells get totalled. Same voltage and current with 50-60 Hz AC is more likely to cause either ventricular fibrillation or cardiac arrest - which gives hardly any chance of the shock victim talking about nerves being fried or muscles or deep tissue feeling fried (and feeling burned and hurting) many years later.

Keep in mind the Edison vs. Westinghouse stuff, especially where it relates to the "Electric Chair"!

- Don Klipstein ( snipped-for-privacy@misty.com)

AC is worse for both making muscles shake and worse still for making muscles freeze. DC shock tends to have main stimulating impact on muscles being with application and release, with 60 Hz AC accomplishing either of these 240 times a second! (Actual effect is largely from current change,

120 times a second with 60 Hz AC.)

Most sources say the "deadly range" is 100 mA to 1 amp - but this is the range with higher probability of ventricular fibrillation from an arm-to-arm shock with 50-60 Hz AC. Shocks a little outside this range are only a little less deadly. Neon sign transformers (with built-in magnetically-based current limiting means) rated at 30 mA output have a slight bit of a body count!

These latter parts are true!

- Don Klipstein ( snipped-for-privacy@misty.com)

In article , lieven 'nuts' citters wrote in part:

AC worse than DC is largely true.

My experience tells me that 2 mA is almost always felt and 1 mA is usually felt and .5 mA is felt to a significant extent. This is with small contact area with 60 Hz AC.

I have been through a couple 5-6 mA shocks that were so bad that I would rank below drinking a mixture of 2-week-old coffee, grapefruit juice and milk even while seeing the milk curdling!

Sometimes less than 20 mA will make you latch onto a conductor, with

50/60 Hz doing this worse than DC, and occaisionally also freeze your breathing muscles or have slight chance of causing some fatal heart disturbance! 100 mA is the lower end of the "most deadly range"! I would measure human body resistance with some small fraction of a milliamp at most, and keep in mind that currents that have any detectable shock effect (even if less than 1 mA) could also stimulate sweat glands and lower human skin resistance!

- Don Klipstein ( snipped-for-privacy@misty.com)

That's not how I remembered it, at least in terms of electrocution ability of steady DC vs. AC of lower audio frequencies.

The main battle there was Edison vs. Westinghouse. Edison favored DC while Westinghouse favored low frequency AC that Tesla favored and did a lot of development work for.

Meanwhile, less-shocking forms of AC associated with Tesla had frequencies too high (typically ultrasonic to radio frequencies) to be practical for long distance AC power transmission to intermittent and variable loads, and utilization by at least all too many industrial motors.

- Don Klipstein ( snipped-for-privacy@misty.com)

How is DC more dangerous? Railroad/subway DC shock victims survive to tell horror stories of 3rd degree burns into deep tissue and/or muscles?

- Don Klipstein ( snipped-for-privacy@misty.com)

On 03 Jul 2006 15:55:25 GMT, snipped-for-privacy@spamnuke.ludd.luthdelete.se.invalid Gave us:

Even a 24V configuration can cause damage applied in just the right circumstance.

You should study up on "skin resistance", and then how water, or particularly salt water can make that drop a lot. Or even body lotions. The worse off one's skin gets for ESD (very dry), the better off they are for shock resistance. Though one could argue them to be a better "attractor" as a dry, insulated body.

Also, if one gets shocked by DC, and an arc was involved, it goes right to the VERY SALTY bloodstream, and you get a much stronger jolt. There is also usually an arc at the exit point to wherever the return was. Those two points of entry become very low resistance locations.

In our power supply shop it was common to hear that "one only gets to make a mistake once with HVDC". Whether true or not, it is always best to act as if it is, and follow all those old basics you thought were so unimportant.

No wrist straps on HV PS benches... :-]

On Tue, 4 Jul 2006 05:05:20 +0000 (UTC), snipped-for-privacy@manx.misty.com (Don Klipstein) Gave us:

120.

On 03 Jul 2006 18:49:42 GMT, snipped-for-privacy@spamnuke.ludd.luthdelete.se.invalid Gave us:

And to think the stupid bastards gave Arafat a Nobel Prize.

Actually, the whole involuntary muscle contraction business is less bad with steady DC - a steady DC shock has little ability to force a muscle to have a sustained contraction (more than several milliseconds), anhd pulsating DC and power-line-frequency AC are much worse than steady DC in terms of causing involuntary sustained muscle contraction!

Largely not true! Unsteadiness of current is more of a muscle stimulant, as long as it has significant spectral analysis to frequencies within maybe 3 octaves of the low end of the audio range!

That part I could agree with!

My favorite riddle:

Q: What do you call a 47K-ohm 1/4 watt resistor with tolerance of +5,000/-98 percent?

A. A live human being!

With body count being outright high due to false sense of safety due to low fatality rate!

- Donb Klipstein ( snipped-for-privacy@misty.com)

On Mon, 3 Jul 2006 19:05:14 +0000 (UTC), snipped-for-privacy@green.rahul.net (Ken Smith) Gave us:

Depending on the amount of stored energy available, DC can literally disintegrate you. However even a single pulse from say a laser pulser supply would light your ass up REAL GOOD. S P A N K! Somebody better go get the wall mounted defib kit that most companies have nowadays...

Take the Bonneville DC Intertie run. Place yourself between a conductor and earth such that you establish an arc.

No one will be able to find any of you. Relatively instantly.

On Tue, 4 Jul 2006 00:32:39 +0000 (UTC), snipped-for-privacy@green.rahul.net (Ken Smith) Gave us:

Hahahahahahahahaha! That is funny!

On Tue, 4 Jul 2006 00:32:39 +0000 (UTC), snipped-for-privacy@green.rahul.net (Ken Smith) Gave us:

• B O O ! *

from

The physiological effect of different currents is as follows:

10 to 20 mA painful sensation

20 to 40 mA muscular paralysis, cannot let go

40 to 80 mA breathing is difficult

100 to 200 mA fibrillation of the heart and death

The internal resistance of your body (right hand to left hand, or hand to leg) is typically 500 ?. In series with this is the surface resistance of your skin which varies from 1000 ? when moist to over 100 k? when dry. Thus a voltage as low as 50 V can produce a hazardous current if your hands are wet.

Never work with electrical equipment if you hands or clothing are wet. Dry yourself thoroughly before you start work. Note that when you are hot the perspiration on your hands increases the hazard.

On Mon, 03 Jul 2006 17:53:18 -0700, John Larkin Gave us:

A DC pulse produces a single contraction that can be huge. Muscle tearing even. A continuous DC shock with begin to cook one's flesh too, (as will AC). AC is less likely to punch a hole in the victim, however, and the skin resistance therefore helps. A DC shock that started with an arc entered the body directly (as well as the exit), and upon entry has a MUCH MUCH lower body resistance to deal with. It gets direct contact with your body's internals (salty blood). If it arcs into you, you are "toast" in many cases. I of course leave out current limited HV supplies in this, as I have made many 20uA 15 to 40 kV supplies that one can handle the arc from, but it isn't pleasant while that current is being limited, and the voltage capped to do so. I wouldn't try this at home.

Again, our rule was, you only get to make one mistake...

Fear can cause a heart fibrillation too ya know. Even small shocks that do not travel through the chest can cause a weak hearted man to spawn a little fear based heart attack.

I can be working on a stereo chassis or whatever at home, and accidentally brush the ac line and get sent across the room by the spasm it induces (it's mental though). I can also, however, take two bare 6" wires, AC fed, and put them between my fingers and thumbs, and slowly work my way up on them till my arms are curling. Knowing that you are passing current makes a difference.

Still, you should all leave that kind of thing to us certifiable shock jocks (screw howard).

On 3 Jul 2006 19:04:41 -0700, snipped-for-privacy@eehomepage.com Gave us:

It is ALL at 60 Cycles, and even the chart where the breaks for "low voltage" etcetera are still in place.

Trust me, you would not want one of out 250Volt DC converter supplies hitting you, even at a mere 3W output (2" x 3" brick)

We certainly call 1kV "high voltage", and yes, we make 'em all the way up to 400kV. I never did like that power company centric naming convention chart.

On Mon, 03 Jul 2006 23:15:06 -0400, Mike Monett Gave us:

Have you not seen the video of that?

There are about six videos of transformers exploding, big interrupters opening while live, etc. out there somewhere... I have them here somewhere as well... one is that guy getting a taste of hades early.