Electric Shocks

[Cursitor Doom]

A while ago I accidentally stuffed my fingers into an uncovered wall socket and got a 240VAC shock (actual full 240 in this instance - according to my Megger). But it wasn't a shock. It was a slowly building tingle I wasn't even aware of to begin with, which slowly wormed its way through my peripheral perceptions to eventually become fairly unpleasant. Having nothing better to do this week I rigged up a Cockroft-Walton multiplier and discovered the same thing with DC. At 150VDC, initially I can feel *nothing* at all, but then a slow burning sensation develops such that after about 5 seconds I have to take my pinkie away. The effect is exactly like touching a low-power soldering iron; it's no big deal at first but then gets increasingly intolerably hot. That's exactly how it feels. I've been goofing around with electrics (with a heavy electronics bias) for nearly 50 years but I can't work out what's going on here. BTW, can't feel anything at all at under 90V. Any insights from our resident sparks as to what's going on here? I mean, why the *slow* build-up?

[Tim Watts]

Something about you I think.

I have had a couple of belters from 240V through one hand and my perception is:

1) It's like being punched in the arm and hand slapped, hard, instantly.

2) It hurts afterwards.

No slow build up.

[NY]

Everyone has a different sensitivity and tolerance to electric shocks. I can feel a slight tingle at about 50 V with dry hands. A 240 V shock definitely comes into the category of "never to be repeated if I can help it". I knew a woman at university who was unbelievably sensitive to electric shocks: she could distinguish a fully-charged from a flat 1.5 V battery by putting her finger and thumb across the ends, and found a brief shock from a 9 V PP9 battery or a 12 V car battery to be exceptionally painful to the extent that her muscles twitched for several hours afterwards. (*)

But whatever the sensitivity, I've never heard of DC or AC at level that can be felt producing a *gradually-increasing* sensation of tingling.

(*) She had a number of medical peculiarities, some diagnosed in later life. She had hypermobile joints (double-jointed) and she developed a rare syndrome whereby her body continued to feel the effects of pain for a long time after the stimulus was removed, to the extent that a surgeon who needed to perform an important operation on her decided it was not in her best interests for him to continue, as he could not guarantee that she would not feel the pain of the incisions for many days after the general anaesthetic had worn off.

[Archibald Tarquin Blenkinsopp]

Bilge!

Accidentally waiting for the tingle to build up?

Multiplier to develop 150V DC?

Has Alt.looney.rec [overy] closed down?

AB

[The Natural Philosopher]

Only if its a gradually incressing voltage

[James Wilkinson]

I've had 240V between two parts of one hand, and it felt warm and tingly. I let go because I knew it was an electric shock, not because it was painful, as it wasn't.

I've had 240V from a hand to my bare feet on the ground. That made my arm and leg muscles jump suddenly. Again, not sore, just gave me a fright.

And there was definitely nothing afterwards in either instance.

[James Wilkinson]

Being able to detect 1.5V is quite amazing. That's not just a medical problem, that's an ability that nobody else has. I can't even feel a 12V car battery with wet hands. 30 volts is required before I notice it. Or about 9V on my tongue (all kids do that with PP3s don't they?)

Sounds like nerve damage.

[James Wilkinson]

I've had 240V between two parts of one hand, and it felt warm and tingly. I let go because I knew it was an electric shock, not because it was painful, as it wasn't.

I've had 240V from a hand to my bare feet on the ground. That made my arm and leg muscles jump suddenly. Again, not sore, just gave me a fright.

And there was definitely nothing afterwards in either instance.

[James Wilkinson]

I've had 240V between two parts of one hand, and it felt warm and tingly. I let go because I knew it was an electric shock, not because it was painful, as it wasn't.

I've had 240V from a hand to my bare feet on the ground. That made my arm and leg muscles jump suddenly. Again, not sore, just gave me a fright.

And there was definitely nothing afterwards in either instance.

[Mike Tomlinson]

En el artículo , bm escribió:

Fried his brain, explains the tripe he posts to usenet.

[Harry Bloomfield]

Cursitor Doom a écrit :

How much effect you feel, is due to the thickness of your skin, how moist it is and the current path. As a kid, to satisfy my curiosity, I would stick my fingers into a live BC lamp socket, I would feel barely a tingle.

I also can feel a slight burning effect, over a short path. I would assume this effect is due to the moisture in your skin 'boiling', or maybe electrolysis.

[0345.86.86.888]

I stuck my finger in a bayonet fitting of a bedside lamp as a kid too. It wasn't nice and I didn't do it again.

:)

[Cursitor Doom]

That's pretty amazing for a child. It's understandable as one ages and the skin gets dryer and hornier through work that its resistance would increase, but for a youngster...

That's what I was wondering, because on the DC multiplier setup, I was monitoring the voltage across my fingers at the final node at the *same* time, and as the burning sensation was increasing, the voltage was actually *falling* (due to the impedance of the C-W ladder I'd imagine) since they're not capable of sourcing much current with the more stages you add (although this was only 3 double-diode stages away from a 100VA

24-0-24 transformer.)

Thing is, though: it's only skin resistance. If you prick your skin on one of these nodes which is all too easily done and all that skin resistance is lost, so the risk of instant death due to fatal current levels (particularly across the chest if you're absent-minded) is vastly increased. I would *never* advise anyone to "try this at home" as they say.

[Michael Chare]

Some time ago, I was told about someone who could hold onto two wire of a three phase 400v supply.

I was also told separately that it was possible to survive an 11KV shock, but that that the burns from a 33kv and above would be fatal.

[Davey]

I got a shock from one of these once. Not pleasant at all.

[Johnny B Good]

The short answer: You're incredibly thick skinned. :-)

The long answer: You have incredibly (dry) thick skinned fingers? :-)

The skin on your fingers must be unusually thicker than most and very likely drier. There is some conduction but since most of the volt drop must be across the high resistance skin barrier, what little current is flowing must be building up heat which must be causing higher evaporation from the sub-dermal layer which I surmise raises the water content in the relatively thick and drier outer epidermal layer increasing its conductivity to accelerate the heat build up which you seem to be sensing rather than the expected effect on the nerves due to electrical excitation normally described as a tingling or electric shock.

With DC voltage, there is also the compounding effect of electrolysis (largely absent with AC voltage) producing conductive chemical products in the skin, the production of which is accelerated by the resulting increase of conductivity in a runaway positive feedback effect.

Most cheap TENS units (and some not-so-cheap) use unipolar pulses which add some risk of electrolytic damage to the area in contact with the conductive pads. The properly specified "Medical Grade" units use a double pulse where the second pulse is of equal and opposite amplitude and follows the first by just a few microseconds (typical pulse width settings range from 30 to 300 microseconds with unipolar devices, a bi- polar pulse device would use the equivalent of a pair of 15 to 150 microsecond pulses).

Interposing a suitable 1:1 isolating transformer between a cheap unipolar TENS unit and your skin can mitigate electrolytic erosion to a degree but the optimal solution is to use a proper "Medical Grade" unit that specifically claims the use of paired bi-polar pulses. Never succumb to the temptation to read into advertising blurb, information that was at best, merely implied.

[Johnny B Good]

Having seen the other replies, I have a feeling you'll like mine the best. :-)

[Brian-Gaff]

Get tested for Diabetes. Brian

[RayL12]

I had a friend in the early 70's who was serious when he said, his girlfriend, who would enjoy the sex they had, would orgasm any time up to 3 hours later, but never during sex?

As for the slow electric shock build up, you think it may be skin moisture build-up?

[harry]

The 240V AC is only the rms ("average") voltage, the peak voltage is much higher.