Question for John T about GFI's

RwEny

Member
If it takes such a small amount of current to cause fibrilation why is it that I have received a lot of shocks over the years and not had it happen to me. When I was in high school I took an electronics class. Our instructor was always working on an old TV. When he got a shock we heard some words not appropiate for teenagers at that time. My grandfather would wet his finger and stick it in a socket to see if there was power there. I'm not disputing the danger' just wondering why in these times why we didn't fibrillate. Thanks John just my brain wandering
 
It all depends on resistance, mainly your skin, and what body part the current travels through. Lots of variables. Just because it didn't doesn't mean it can't. John T will give you a lot more info.
 
It depends on where the current flows. In your grandpa's case the current just passed through his finger. Now if Grandpa would have grabbed the hot wire with one hand and the neutral wire with his other, the current would have passed through his heart causing fibrillation.
 
The big thing about electrocution is the way one gets the shock. If you get it in a way that it does not cross the heart your a lot less likely to get in trouble. Like say from one arm to the other arms which is a path right threw the heart. When I was in the Navy E.T. school we where told it only takes a milli volts to kill you and 32 volts to shock you
 
It's hard to figure, but like Rich says, if it passes through your heart, it does not take much at all.

I can relate given I had the unfortunate experience of almost frying on a steel column when I was a kid helping out in our ford tractor dealership shop. Some jerk on the payroll had taken the cover off of a unit heater thermostat. The building was completed in 1947, in those days, thermostats were controlled with full power, not low voltage. This was 220. I reached up with my right arm to a small shelf where welding lenses were kept to get one for some reason I cannot recall. 3 bare wires were exposed and I contacted them at the underside of the wrist. I was about glued to that steel column for what seemed to be an eternity. I could not get myself off of it and it took 2 men to pull me from it. The whole time its arcing onto my skin and burning me. I can still see the scars, one for each wire. There is no doubt in my mind this would have killed me and it would have been a long torturing affair before dying. Its hard to describe what electricity feels like when its running through your entire body from head to toe, between the humming, vibration and burning skin. Your muscles lock up, there is no doubt about that. It would have been nice to have been thrown by the initial jolt, but I was not so lucky.

Another hard lesson learned, some parents never gave a crap about looking out for their kids like they should. I've suffered the consequences of that more than once, this was one of them. To this day I do not forget 2 things, the jerk that left the cover off with exposed bare wires and whomever allowed me to work around such a hazard. I never even got the benefit of seeing a doctor either, was left with 3 nice burn holes in my skin, and they were nasty to heal up. Its hard to explain why it did not short my heart, thankfully the good lord had other plans for me.
 


Three factors to consider.

1. The path the current takes thru the body.

2. In amount of current.

3. And the length of time.

That was what they taught us sparkys three decades ago.
 
rw, good question and there are a ton of variables at work when it comes to the feeling of being shocked versus enough current passing in the area of your heart causing it to fibrillate.

First of all if you have ever taken part in science experiments where high tension static generators were used that made your hair stand on end or you walk across carpet in the winter and feel a shock its true you feel it, however, the energy level is so extremely low you probably couldn't get 20 to 30 milliamps of current (cant let go value) to flow continuous through your body. You can get shocked but not killed as the current capacity is so low

The first rule electricians were taught in our shop was the old one hand in the pocket rule. If youre working in typical AC distribution systems believe me there is enough energy to pump 20 to 30 to 100 or more milliamps of current through your body. Therefore, with one hand in their pocket even if they got shocked its probably NOT arm to arm current flow WHICH IS THE WORST AS YOUR HEART IS IN THE PATH unlike if current flowed finger to finger or even hand down to a leg on same side of body.


GFCI's trip at 5 milliamps

10-20 mA is the typical "Can't let go!" current and creates the onset of sustained muscular contraction.

I have seen data where as little as 30 to 50 mA of current through the heart can cause fibrillation

100-300 mA is like for certian big time ventricular fibrillation, fatal if continued.


As far as voltage and current through your body and whether or not it can shock or kill you Ohms law and Energy still applies. Again a sciene lab generator can produce thousands of volts but is of such low energy it cant pump enough current in the body to kill you. I still = V/R HOWEVER a low energy device will not sustain its voltage once a current path is introduced. However if youre wird to a 5 KW Transformer even if its only 120 volts it can deliver enough current to both shock and kill you.

Its impossible to say exactly how many volts might kill a person (assuming theres enough energy) because it depends on their body and skins resistance and moisture etc. I think even different ethnic groups may have different skin resistance. Still the current figures above apply so it just might take more or less volts to deliver that to two different persons.

Nuff said

John T
 
Old, you claim, "it only takes a milli volts to kill you " Are you sure about that??? hey were never too old to learn and Im ready willing and able if Im not too old lol


I dont think a millivolt can cause 30 to 50 or 100 miliamps of current to flow through such high resistance of the typical human body. Nowwwwwwwwww 30 to 50 to 100 milliAMPS of current through your heart can indeed kill you, but I just dont see how a millivolt across even hand to hand could kill you, but Im willing to learn mind you.

Thanks for all your help, I hope your ct scan and medical stuff turns out okay, let us all know

Happy Fourth of July to you

John T
 
Funny, all the times I've worked on electricity without turning the power off and the only time I've been shocked was from a short in a tool. The worst was one day I was working with an old all metal hand held circular saw bent over and to stand up I put my other hand on a table saw someone was running and got zapped. Took me a couple of seconds of telling myself over and over to let go to get away from it. I think I must have gotten 220v.
 
The most painful experience I've had with electrons was from 12V!
Failed to disconnect the battery on a car while working on the starter. really hot and sweaty, I leaned over the fender, laid my sweaty arm on the battery post and with the same hand touched a wrench to a bolt (ground). Lots of current available, short distance post/arm to hand/ground. Hurt like the dickens. arm cramped for hours.

Sort of felt like the frog leg on a lab table with a battery probing it looks!
 
"Its impossible to say exactly how many volts might kill a person (assuming theres enough energy) because it depends on their body and skins resistance and moisture etc."

Interesting concept... I wonder if you could also figure in the "fear factor", as in someone terrified of electricity, or caught completely off guard, as Billy NY explained below.

There is an electric motor shop near me, a family owned shop, been there forever. One of the owners (who has now passed), for years would demonstrate to anyone who asked, his ability to hold 120vac, hot in one hand, neutral in the other, and carry on conversation as if nothing were happening!

I still don't know how he did it, how he avoided the physical burning if nothing else! His explanation, he had been shocked so many times he could just ignore it. Claimed he could do it with 220 in his younger, pre-heart attack days!!! He did have some very hard, dry, calloused hands.

But I think one big factor was, he was expecting it. Deliberately subjecting himself to something that, in his mind wouldn't hurt him, so no combined fear induced adrenaline rush, and the heart stopping fibrillation.

So similarly, someone familiar with the dangers of getting shocked, as in working near live circuits as we've all done... Gets nipped, it's usually no big deal, as long as it's not 480 or more (which I have great respect for and avoid touching at all)! We usually expect it, and take the proper precautions, as in keeping the path clear of the heart area.

Just a thought...
 
That's a deal where there was indeed sufficient energy, although I = 12/R shouldn't have pumped too much current through you.

John T
 
Well if I am wrong then the Navy is and has been teaching it wrong for decades. But again you know there are many way a person can get shocked and you also know there is no way you can tell me every time one dies from a shock is the exact same
 
Volt should have read milli amp was in a hurry this morning when I posted that so replace volt with amp. amps kill volt just push it into you but it you where really thinking you should have known what I was saying
 
OLD, you state "Volt should have read milli amp was in a hurry this morning"

NO PROBLEM I'm often in a hurry myself, glad you understand it

Best wishes

John T
 
Glad I was able to help you Rich, take care now Happy Fourth, hope your health problem works out

John T
 
It's based on the resistance where the electrode touches you and your body to a ground source. 1/10th of amp through your body can kill you. I got zapped by a 13,000 volt line when working as a lineman and it blew a chunk of my arm off. I was in a fiberglass bucket though and my only contact with an "earth ground" was a green tree branch touching me. For all the years I worked for the power company, and my dad as a line-foreman - I knew of three guys getting killed and all died from 120 volt, 60 cycle current. I know many who got zapped by much higher-voltage and they just got burned - not killed. I suspect that is often the case because people working around very high voltage and current sources wear better protection. Thomas Edison used to go around the country electrocuting circus elephants to show the "evils" of 60 cycle AC power.
 
Years ago when I was an electrician and went to these trade shows some of the guys talking shop started to 'one up' each other.
One gut said he got hit by 120, another said "Oh man, I got hit by 220." And so on.
I just grinned to myself thinking how lucky you guys are still able to tell about it.

At one of our safety meetings a doctor was invited to speak to us.
Maybe he was trying to scare us but it worked.
He said if you get shocked it leaves a scar on your heart for life.
I rarely if ever worked stuff hot.
 
No you did not get 220 unless you contacted both phases at once. If you work on circuits live you will be cured of that the first time you get hit with 277 volt lighting circuits. Once you get hit with 277 you will not work hot anymore . You also will make much tighter screw connections with power off and not worrying about shock hazard.
 
I suspect I got one leg from the circular saw and another from the table saw. I've gotten ahold of 110v before and this was so much stronger.
 
I knew a Navy guy who told me he was shocked by a 480 volt welder. I told him he got 277 to ground . He said no , he fell into both phases one on each arm . He is pretty lucky to be alive.
 
I was work off a buss duct that was an isolated system, that had one leg that had gone to ground.
I got nailed by one of the other legs and ground so that was the full 480. Took it kind of easy for an hour or so after that one.
Also got it from a 277 once.

Dusty
 
I was work off a buss duct that was an isolated system, that had one leg that had gone to ground.
I got nailed by one of the other legs and ground so that was the full 480. Took it kind of easy for an hour or so after that one.
Also got it from a 277 once.

Dusty
 

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