The old jumper cables always had little plastic covers for the clip handles and I always assumed that it was that plastic that kept me from getting shocked, but the new ones don’t have anything on the handles other than paint.
So here’s the procedure. I connect the red ends to the two positive posts, and I connect a black end to a negative post. Now at this point I’m holding in my hand a live circuit, right? When I touch the end to the car body I see and hear sparks. So why isn’t that current coursing through my hand and down my leg?
It’s only 12 volts (actually about 13-14 volts). You can grab the terminals with both bare hands and not feel a thing. You might feel a bit of a tingle if your hands are particularly sweaty, but that’s about it.
As Q.E.D. pointed out the voltage is very low. Also the paint is an insulator. Bottom line is on a standard automobile electrical system it is very hard to get a shock.
There are two large exceptions to this. The secondary ignition system on a gasoline engine can shock and even kill if conditions are right.
The other exception is hybrid cars. Those systems use serious voltages. IIRC 10X-20X the voltage of the battery of your average car.
I know the technician training for the Ford Escape hybrid included a section on how to get someone that is being being shocked away from the car without getting electrocuted yourself.
It’s not the voltage that will hurt you, it’s the current and automotive batteries pack a punch. I have been knocked on my butt when I accidently shorted myself across battery terminals.
No. You have no connection to the positive. In order to complete the circuit on the negative side, the current would have to go from the clip you hold, through your body, through your shoes, through the pavement, through the tires, then through the chassis of the car. While the chassis offers virtually no resistance, the other items have considerable resistance at that voltage and any current flow will be miniscule.
As you surmise, at the moment you make connection, the current readily flows from the clip to the battery terminal. They offer essentially no resistance, in contrast to your body and the other items mentioned above.
If your hand is anywhere near the end of the jumpers and you cross connect them you might lose a finger in the ensuing spark. I vaporized 1/8 of a lead battery terminal because the person on the other end of the cables reversed them.
Also had a screwdriver blown out of my hand poking around a 120V circuit. Again, the spark vaporized the tip of the screwdriver.
Assuming your skin was intact, I don’t see just how this is possible. It’s true that auto batteries pack a shit load of amps, the new battery for my truck is over 800 cold cranking amps. At room temp it can probably deliver over 1000 amps for a short burst.
However with that said, I did have a terminal in each hand during the installation, and I have grabbed both terminals of a battery (or the positive and a good ground) lots and lots of times in my career and I have never even gotten a tickle.
Back in the old days, one of the tests for an oxygen sensor circuit was to grab the positive battery post with one hand, and the O2 sensor lead with the other. The resistance in your body, cut the voltage to about .7V at 0.nuthin amps. You would then observe if the control unit responded.
Shrug, I don’t know what happened to you, but I don’t see how you got a shock off of a 12V battery.
Current, or amps, maybe what is needed to injure you, but high voltage is what is needed to overcome the incredibly high resistance the human body has to completing a circuit. And without a completed circuit amps don’t exist. And 12VDC is not even remotely high enough.
It’s not the voltage. It’s not the amperage. It’s the coulombs.
Anetdote: Mrs. Alta Harrington of Harrington, Delaware was visting and decided to hand to one of the horses an apple. Unbeknownest to her the apple holding arm was brushing against the electric fence. The horse was the first to notice.
Parlor Trick: When working on a car and someone comes up and leans against the car to chat - without touching anyother part of the car, with your fiinger on the shaft of a screwdrive touch the blade to the distributor coil output. You will feel a slight shock but you are expecting it. The circuit completing car leaner is not expecting it.
This would presume that you could reach the coil output without grounding yourself to the car in the process. It also presumes that the insulation on the coil output is broken down enough to conduct electricity. If yo are leaning up against the fender yourself it is quite likely the electricity would travel up your arm, down your torso and out either your thighs or via Mr. Happy. Now this might give you a momentary belief that you are Thor God of Thunder, but let me assure you, you aren’t.
Finally on some modern cars this is a very bad idea. Unlike a points equipped car that put out about 12-18,000 volts, some modern cars put out upwards to 90,000 Volts and at a much higher amperage than a points equipped car.
I worked with a guy that told me that he laid his arm (reaching for something) on a set of GM coil packs on a running V-6. He got shocked. He said that the muscles in his forearm stopped responding for about 30 minutes. :eek:
Now I was not there when this happened, it just what I was told. I can tell you for a fact that the instructors manual that I used at Sun Electric has some rather serious warning about high energy ignition systems and the potential for electrocution.
I have experienced fairly significant shocks from 24 VAC transformers capable of providing less than 2 amps. In every instance, I was sweating profusely. IIRC, the normal resistance of dry skin is on the order of >100,000 ohms. Sweaty skin has less than 10,000 ohms of resistance. Assuming heavy sweating and a large area of contact, I can believe that a 13.8 VDC car battery could give a frightening shock.
Reading your cite, I was pretty much in agreement with what was written until I got to the part where he showed one hand grabbing a pipe with 2000 ohms resistance, and with two hands it would have 1,000 ohms resistance.
This would only be true if the was a separate ground connection to the body (which isn’t shown in the picture) absent this separate ground connection, this is not a parallel circuit, but rather a series circuit. The resistance of each hand is additive, instead of 2,000 ohms for one hand, you have 4,000 ohms for both hands.
All I can tell you is that in all the years I have been working on cars I have never had a shock from a 12V automotive system. Primary ignition? Yes. Secondary ignition? hell yes. The battery? No.
In the interest of fighting ignorance, if it isn’t raining too hard in the morning, I’ll go out and short my wet hand across a battery terminal to observe the effect.
One thing you can do with batteries, of course, is burn rather than shock. Model fliers often use some nifty NiCds (or NiMHs or LiPolys) and these can hand out current on a par with similar-sized lead-acid batteries. A mag carried a picture that showed why you should remove watches and rings while playing with these - someone had a nice ring-shaped burn on his finger, and a wedding ring with a hole in it. Skin may have resistance in the kΩ range, but a gold ring doesn’t, and if you put a nice big amperage through metal in contact with you, you will get very warm in not much more time than it takes to say “Ouch, that’s hot!”.