Why AC Kills

Why fluctuating current kills? Is the power being delivered much higher than DC? Thanks Jack

Reply to
Jacky Luk
Loading thread data ...

"Jacky Luk" wrote in news:cgmt65$ snipped-for-privacy@imsp212.netvigator.com:

Whether it is AC or DC really makes no difference. It takes approximately

0.1 Amp to kill a human being, provided there is enough voltage potential present to get it through the body in the right path. It's not the volts that get you.....it's the current.
Reply to
Anthony

The reason that AC is more deadly is that it has the ability to disorganize the beating of your heart at very low current levels. The resultant condition is called ventricular fibrillation. You can read about the effects of V-fib at

formatting link
Tom H

Reply to
HorneTD

There are differences in the effects of electric shock with AC vs. DC. These are dependent upon the voltage levels, the point of contact, and the path of the current once it enters a human being.

In general, just like it is difficult to break a dc arc with a switch, it can be difficult to let go of a DC circuit once contact is made. This can make lower voltage DC circuits (60 volts or so) more dangerous than the equivalent AC circuit if the current is strong enough.

AC shocks above a certain voltage level are more likely to interfere with heart functions due to the fluctuating characteristics of the current..

Beachcomber

Reply to
Beachcomber

In addition, a DC shock results in a single massive depolarization of the muscles through which the electric current is flowing, which causes a muscular jerk that often throws a person free of whatever they are on contact with.

AC makes the muscles to try to follow the polarity changes, but

60 Hz is faster than the muscle can react. For cardiac muscles that causes fibrillation (uncoordinated movement of different parts of the heart) or even just totally stops the muscles completely. For other muscles, much the same thing happens, with the effect that a person can't let loose of whatever they are in contact with that is causing the shock.

The effect is that exposure is likely to be much longer with an AC shock than with a DC shock. That will cause greater nerve and muscle damage, in addition to a much higher likelihood of cardiac fibrillation.

(One interesting experience is being shocked by 20 Hz AC! That is the ringing voltage for telephone systems, which isn't usually too bad if you get it on a telephone line because it is turned on and off with an interrupter. But in telephone offices there are wires that have 90 to 105 VAC at 20 Hz continuous. And grabbing one of those is *not* fun. Your muscles can indeed follow the 20Hz AC, and a couple seconds of that is a *lot* of exercise! One good jolt, and you feel like somebody mopped the floor with you.)

Reply to
Floyd L. Davidson

I believe you have that backwards. AC is harder to get loose of.

DC circuits below 60 volts generally are not considered dangerous, at all.

For example, telephone battery plants are nominally run at 54 to

56 VDC, and the bus voltage supplying equipment is 52 to 54 volts. Bus bars on both battery plants and on fuse bays are commonly not insulated, and are exposed to workers who do in fact commonly touch them without effect.

That is correct. (I posted details in a previous article and won't repeat it here.)

Reply to
Floyd L. Davidson

in article cgmt65$ snipped-for-privacy@imsp212.netvigator.com, Jacky Luk at snipped-for-privacy@knight.com wrote on 8/27/04 1:59 AM:

I remember back to my student days when I went to an AIEE lecture on shock. The lecturer claimed that he never heard of a DC fatality that did not involve cooking or an inductive kick.

Bill

Reply to
Repeating Rifle

There was a test of electrocution devices - Chairs, in the 1800's between AC and DC, Edison (yes, the guy that invented the light bulb) sponcered DC. Not sure who won, Edison got some patents on it.

Reply to
Carl Kalman

The story is that Edison "invented" an electric chair and carefully pointed out that it would only work on AC. (Edison was pushing his DC system; Westinghouse, with Tesla, was pushing the AC system.)

It doesn't matter whether it really happend that way (Edison pushing the AC powered electric chair) since it is just a GOOD story.

Reply to
John Gilmer

Reply to
Don Kelly

Seems to me that if DC were all that dangerous, there would be a LOT more dead bodies along side of DC electrified railroads. There likely would be even more small animals being fried. The 3rd rail voltage is 600 volts.

I understand that at one time the Long Island Railroad (the line running on the South side of the island) was level grade with no fences keeping folks from the tracks. I think the same is still true of much of the NY Central RR running along the Hudson River north of NYC. (I know the names are no longer valid.)

I knew a woman who as a kid would think nothing of walking across the RR tracks and often just stepping on the board that covered the 3rd rail.

Reply to
John Gilmer

in article snipped-for-privacy@uni-berlin.de, Carl Kalman at snipped-for-privacy@kkalman.com wrote on 8/27/04 4:35 PM:

If I interpret you correctly, you are wrong. Edison sponsored DC and did not want it used for electrocution. He wanted to call the process Westinghousing.

Bill

Reply to
Repeating Rifle

600 VDC is indeed dangerous. This is the voltage used for the Chicago L system and it has killed or seriously injured numerous people over the years. At the few grade level crossings (Kedzie, and two streets on the Evanston/Wilmette Line), automatic fence barriers that block the tracks when the train has passed were installed years ago. The CTA doesn't want children and others who may be stupid to wander about its dangerous yards.

The CTA uses an exposed open third rail at +600 VDC system. There have been other schemes developed over the years that have the exposed voltage conductor partially concealed and these systems are considered somewhat "safer". That would be "safer" for the yard crews, but you still couldn't expose these systems to the public.

Washington, DC. streetcars used to derive their current through a recessed shoe in a channel that ran down the center of the tracks. (You can see this in many old newsreel films - the track looks like SF cable car track, but they were really electric). Although this system was fairly safe, I understand it was abandoned because ice would build up in the center channel during bad winter days and cause many problems.

Although I don't know too much about it, I've heard that England has a history of running exposed third rail pickup at grade level for some of their electric rail lines that run through the countryside (without protective fences). I'm not sure if this is still the case. Perhaps an English reader would care to comment?....

Beachcomber

>
Reply to
Beachcomber

snipped-for-privacy@barrow.com (Floyd L. Davidson) wrote in news: snipped-for-privacy@barrow.com:

.

Been there, done that, got the nerve damage to go with it. I do quite a bit of residential/industrial electrical work. Got into a 110VAC circuit in a bad place....(my own lack of my normal safety procedures was the root of the accident), however, I was in it for ~30-45 sec. Still not sure how I got out of it...except I did black out, probably fell out of it. Weakness for days, numbness/tingling in the arm/neck/face on that side to this day, two years later. AC is not fun. 24V DC isn't all that pleasant either.

Reply to
Anthony

Ouch. That is really nasty sounding.

If you can even feel 24 VDC, you are unusual! Most people can't, at least without making an effort at a very good contact. Your skin is probably either more moist or more salty than average.

I'm somewhat more sensitive that most people, but not that sensitive.

On the other hand, I've seen people who could test 115VAC with two fingers, and they claimed to get only a slight tingling feeling! Drove me up a wall to watch, because for me even the slightest brush with 115VAC is a *jolt* that just jangles me silly.

Reply to
Floyd L. Davidson

I was living in DC when the streetcars were taken down.

THE reason was 100% political. Congress (which actively ran the District back then) didn't like the guy who owned the streetcar company. The owner wanted to put air conditioning in the streetcars but congress would only let him air condition ONE car (which was supposed to be for sightseeing.) Busses by then were air conditioned. Finally, congress just flat out required that the streetcars stop running and that was that.

I rode the street cars to school for 2 1/2 years. The route took me over the point where the service changed from underground to overhead wire. I was NEVER on a stuck car. However, there were claims that the salt used to remove ice from the roads in winter would cause problems.

The streetcars were taken down in early 1961 as best I can recall.

Reply to
John Gilmer

In our company, people that test 115VAC with two fingers have a special name. *UNEMPLOYED* Sure, most times if you use the back of your hand or such, you won't get much of a jolt. But violating electrical safety procedures is a firing offense. Course, we also work with much higher voltages. But it always amazes me how 'experts' will get sloppy around the normal 'house current' and not follow the rules.

Interestingly, OSHA has seen an increase in the incidents of shock *to electrical workmen* on low-voltage equipment. Not the general public, but the guys trained in electrical work. (OSHA considers low-voltage as 600V nominal and below). The arc/flash burns from a 480V MCC can be *very* serious, but guys that work on 13.8kV and 4160V think 480V is 'kids stuff' and aren't being careful.

daestrom

Reply to
daestrom

Volts jolt and mills kill!

Whether it is AC or DC really makes no difference. It takes approximately

0.1 Amp to kill a human being, provided there is enough voltage potential present to get it through the body in the right path. It's not the volts that get you.....it's the current.

-- Anthony

You can't 'idiot proof' anything....every time you try, they just make better idiots.

Remove sp to reply via email

Reply to
Brian

in article snipped-for-privacy@netnews.comcast.net, Beachcomber at snipped-for-privacy@nospam.xyz wrote on 8/27/04 9:51 PM:

What was the immediate cause of death? Did the dead ones get cooked? Did they have circulatory failure? Did they get hit by a train?

Bill

Reply to
Repeating Rifle

in article dg0Yc.31386$A91.30465@okepread02, Brian at snipped-for-privacy@whatisitgood.for wrote on 8/28/04 7:05 AM:

I knew that there was something funny about that last loaf of bread that I baked. :=)

Bill

Reply to
Repeating Rifle

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.