Further Thoughts from C.D. Prewitt on Electricity Safety, A.C. vs. D.C.

In this piece C.D. Prewitt argues that, contrary to the opinion of several readers, personal experience has taught him that where electricity safety is concerned direct current is much less dangerous than alternating current.


| May/June 1973



Prewitt - Lightning Strike 2

A direct current shock of this magnitude might kill you, but small ones aren't dangerous.

PHOTO: MOTHER EARTH NEWS STAFF

MOTHER EARTH NEWS contained some feedback on my statements about the advantages of direct over alternating current, and I'd like to offer a rebuttal that's based on my own experience . . . not on theory, as the criticisms seem to be.

First of all, an alleged danger of D.C. is that one might not be able to let go of the electrodes that are producing the shock. Now, I've been hearing that statement all my life, and I'm convinced that it's nothing but theory, with no real foundation. I've had all sorts of shocks—up to and including one of 10,000 volts, when one contact was with my left had and the other with both feet thoroughly grounded—and I've never felt any inclination to hold on. On the contrary, either kind of current causes an irresistible urge to disengage, which some people feel so strongly that they claim the jolt has "knocked me down." I've seen victims do some wild jumping, but I've never seen one want to continue grasping the conductor.

In fact, I wonder whether shocks are necessarily as deadly as is generally believed. That time I was hit with 10,000 volts (A.C.) I didn't dare pick up a cup of coffee for three days afterward because I was sure I'd slosh it all over the room. I was convinced that my nervous system had had it . . . yet a week later I was as good as new. If some people's notions are true, my heart must have moved out of the way.

Yes, I admit that even a small current could kill you if it passed through the heart . . . but to accomplish that you'd probably have to introduce electrodes into the organ. Actually, of course, a current (unless it's of very high frequency) doesn't flow through one geometric line, but through a considerable area. In a case like my accident, one's heart might or might not get a lethal amount.

By the way, Peter Grant's statement that the body's resistance is only 500 ohms is clearly out of line . . . it's known that across any substantial part of the anatomy—as from hand to hand—the figure is well up in the thousands of ohms. Since I had no exact data of my own on this point, I made a test by thoroughly wetting my hands and grasping the prods of an ohmmeter. I got a reading of 50,000 ! I then attached the prods to sizable pieces of metal (something no one would do where there was shock hazard). When I again wet my hands and gripped these conductors, I couldn't get the indicator below 20,000 ohms.

Now don't misunderstand me! Current can be dangerous, especially if you don't know what you're doing, and there are some chances no one should take. (For example, don't risk shocks of any kind when you're working in a high place . . . on a windmill, perhaps. If you feel the current it's likely that you'll instinctively jump away from it, and you may lose your hold and fall.) Nevertheless, there's a theory—one I subscribe to—that most so-called shock deaths are really caused by fright. Certainly a severe jolt can be an alarming experience.

john_129
11/28/2007 2:17:57 PM

As a person who has had the experiance twice, I can aszxure anyone that if you grasp a conductor with 120 vac with your hand around the conductor, and are grounded through your feet, you will not be able to turn loose even tho you REALLY want to! And you will not be able to inhale, although your muscles are forcint the last bit of air out of your lungs, and you will not be able to speak. What happens is the electrical curent causes every muscle it is traveling thru to contract to its fullest capicity. In my first instance, I survived only because I lifted my body off the ground with one arm. In the second instance, the wire I had foolishly grasped broke from the end delivering the power. If it had broken from the other end, I would be dead. At least one investigation into real life electrocutions determined that usually the current through the body was between .1 and .2 amps. Skin resistance with modest contact ares moisture usually provides between 20000 to over 100,000 ohms which saves us from most shocks. But, leaning on an airconditioning duct, and runing a metal framed drill motor into a 120 v wire has been fatal. I too worked in electronics durring the vacuum tube eara, and I occasionally came in contact with B+ which could exceed 200 v, with significant current capacity, and I can assure you my reaction was violent. So, don't be either too fearful, or too complacient around electricity.






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