60V DC dangerous?

Bad enough that CE wants you to keep it from your product's consumers. I would assume that it can be fatal on a Very Bad Day.

I would answer your second question but the ghost of my Lawyer is whispering in my ear so I won't. I _will_ say that _I_ would treat

220VAC with a great deal more respect than I would treat 60VDC, because 220VAC can kill you faster.

Surely this information is out there on Google if you can think of the right search terms?

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Posting from Google?  See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Where's the CE "keep out" limit?

(48V dc is used in PoE apps..)

Problem with google is that it will more or less act like a "yes-sayer"..

snipped-for-privacy@spamnuke.ludd.luthdelete.se.invalid =E5=86=99=E9=81=93=EF=BC=9A

I my opinion, 36V DC is dangerous enough......So keep away from it.

I'm not sure about CE, but NEC says 50V DC and above is potentially fatal. That's why 48V is used for telecom apps, and PoE would likely follow those guidelines if a lot of power must be transferred.

As far as AC vs DC goes, the only real difference is whether or not you shake before you fall on the floor.

It only takes about 50mA to kill you. Depending on how good the connection is, it takes a lot less than 50V to cause that much current to flow through your chest. The dry skin of your hand is where most of the voltage drop happens when you get a shock.

Depending on where you are voltages under 48V or 24V or some other is considered by the government to be safe. At these "safe" voltages you no longer have to make sure that a person can't come in contact with it.

Low voltage, high current situations can cause injury if a metal object comes in contact with it. This is why, (smart) people remove any rings or wrist watches before working on such things.

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kensmith@rahul.net   forging knowledge

42 V pk IIRC ( peak value of 30V ac ). 48V is inded a bit of an anomaly but who cares ?

Graham

if you want to make something for your baby, you should stay below 24V DC. otherwise, you need to take 48V DC Normally, AC is more dangerous then DC. It's not voltage that's dangerous, it is current. You can feel 2 or

4mA, 10mA gives a serious chock, 20mA will make you stick on the conductor, 50mA will knock you onconscious and 100mA will kill you. As a student, i tried to make an ohm-meter for persons, and i started calculating with a current of 100mA. You need way too much voltage! :D

if you want to know more about this, read ESD regulations on

greets

Not very.

..?,, or 50V ?

48 DC is usually considered safe, so 50 can't be a lot worse.

Not really. Aside from the magnitude difference, AC is much more dangerous.

John

For the progress of humanity .. :-)

Reminds me of the "taste great; less filling" AC vs DC debate between Edison and Tesla. Each promoted using the other's form of power for the electric chair!

Luhan

snipped-for-privacy@spamnuke.ludd.luthdelete.se.invalid ??:

I my opinion, 36V DC is dangerous enough......So keep away from it.

Big girls blouse!!!

In article , John Larkin wrote: [....]

No, DC is much more dangerous. I like Tesla better than Edison.

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kensmith@rahul.net   forging knowledge

Edison used to electrocute cats in his garden to demonstrate to visitors how dangerous AC was.

There's a graph, somewhere, of how lethal AC is as a function of frequency. I believe it peaks at about 30 Hz.

John

Wow, really? Edison and Schrodinger would have gotten along very well together, I can see...

Wow, really? Edison and Schrodinger would have gotten along very well together, I can see...

Edison used to be my childhood idol (no, he was not a contemporary), but then I discovered Edison's uglier side and Tesla's eccentric and unappreciated brilliance, so now he earns my respect and interest.

As for dangers of AC and DC currents and voltages, it is true that it is the current that causes physiological problems that can be fatal. Current causes muscle contraction, so AC current causes characteristic shaking, which has the advantage of allowing you (possibly) to let go. DC current causes continuous contraction, and because the muscles for gripping are more powerful than those for opening the hand, the tendency is for it to be impossible to release the conductor. This is why, if you MUST touch an energized conductor, use the back of the hand, so the contraction will take you away from danger.

The conduction of the human body varies considerably due to skin conditions, and I think it is nominally about 10 k Ohms from one hand to the other, or from hand to feet (the usual paths). So 120 VAC will cause about 12 mA, which is well above the threshold of sensation (about 5 mA), but below that for near certain fatality (50-100 mA). However, heavy perspiration can bring that resistance down to 2-3 kOhms or less, where 120 VAC becomes very dangerous. Also remember that 120 VAC has peaks of 180 volts, which cause pulses of more dangerous current.

Another big problem with AC voltage is that power line frequencies are just about the worst (or best) for causing fibrillation, which is a life-threatening condition that can continue after removal of the power. Essentially the heart pacemaker becomes confused and causes extremely rapid beats that do not pump blood. A high current DC jolt from a defib essentially resets the pacemaker and allows a normal restart. Dick Cheney has one of these "Watchdog Timers" in his chest.

Higher frequencies often tend to travel more on the surface of the skin, bypassing internal organs such as the heart, and are thus a bit safer, as well as not being as likely to cause fibrillation.

Even very low voltages can cause some interesting physiological effects. I have heard of an experiment (or party prank), where a gold coin or a valuable ring is placed in a tank of salt water, and a 12 volt battery is connected to electrodes passing perhaps an ampere or so of current through the solution. You can have the coin or jewelry if you can pick it up. However, the current causes nearly immediate paralysis of the hand while in the water. Maybe you can cheat and cover your hand in vaseline?

I have also heard horror stories of people who were in a boating accident with an electric motor, where the cables fell into the water where they were trying to stay afloat, or possibly holding onto the aluminum boat. Rather uncomfortable!

I have not fully researched the above statements, but I believe they are at least close to realistic. The bottom line is, almost any voltage can be dangerous, and deserves to be treated with respect and caution.

Paul

(Re-posted via Google because of problem with Coretel.net)

In article , Paul wrote: [....]

No-one is fast and strong enough to gain let go during the very brief time that the current is small.

This isn't completely true. The contraction may only take you to a lower danger or just as serious of one. Based on the one experiment of this type I did, I know that the muscles in the human arm are designed so that the joint where the thumb connects to the hand is brought with considerable force directly to the eyeball on the same side.

[...]

Yes, but higher frequencies tend to punch holes through your flesh. I have at least one scare from this.

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kensmith@rahul.net   forging knowledge

Uh, I believe that's backwards. AC produces the stronger muscle contractions. 8 milliseconds isn't a lot of time to let go.

John

It's pretty hot here at the moment, my hands feel slightly clammy. Taking a firm grip of my fluke probes between thumbs and forefingers the grip has to be so firm as to be painful before I see a reading below 300k ohms.

I thought 10k sounded way low, however, I don't know what if any breakdown voltage is associated with that resistance.

Overcoming my instincts not to be a human resistor I tested up to 24Vdc,

0.15mA, 160k. That was gripping a couple of croc clips - maybe I was sweating a bit more by then - lol.