Electric Shock Threshold

[Snipeye]

I was wondering what the threshold for being able to feel an electric shock was under normal conditions. I realize "normal conditions" is very vague, but to try and be a little more specific: temperature in the 60's or 70's, humidity fairly low, dry skin, etc. I want to be able to have some sort of feedback from a device I'm considering building, and I think a small electric shock - just enough to feel it, basically, maybe a little more - will be a good, silent sort of feedback.

Additionally, what happens when these factors change - temperature gets lower/higher, air and skin humidity increase/decrease, etc. What sort of current/voltage am I looking at?

[phild13]

That is not really an easy question to answer and has no straight forward here is the number answer. Voltage is a component of the shock threshold, but is not so much a concern as the amount of current flow or potential current flow at a given voltage through a persons body. Just to start out with, the maximum generally accepted voltage that can be touched bare handed (no PPE) is 45 volts and even that can be too much under some conditions and so that voltage should be reduced where possible to 10 volts maximum. Most industry is switching from 120 volt control systems to 24 volt control systems as equipment gets replaced or updated, because it is much safer to work on.

A general answer to your question is an average threshold of perception of an electric current is 5mA dc in men and for women it is about 2/3 of that. Body resistance with intact skin varies between about 100,000 ohms and 1000 ohms and internal body resistance can be as low as about 500 ohms.

Some people can sense a tingling sensation with as little as 1 mA and you would need about 100v to feel that 1mA at the 100,000 ohm skin resistance and 1 volt at 1000 ohm skin resistance and you will definitely feel that 1mA at the 500 ohm body resistance if the skin is punctured. The threshold current varies widely between individuals and ranges from about 1 mA to about 10mA and varies with type and points of contact for each individual. The average threshold of 60Hz AC current is about 1mA but also varies between individuals, points of contact, and type of contact. As the AC frequency increases, so does the threshold where a person can detect a tingling sensation. At 100kHz, the threshold is 150mA.

The maximum accepted harmless current is 5mA so under no circumstances should a current higher than that be allowed to pass during the normal process or during component failure.

For a reference, I think residential (class A) GFCI will trip at a current greater than 6mA in 6ms and commercial/industrial ones (class B) trip at a current greater than 20mA in 7 ms time.

[mwilson]

Interesting. I've had a project going -- not very seriously -- to produce perceptible electric shocks. My idea was to charge a capacitor up to, say, 5V and discharge it through a step-up transformer. In theory you could choose the capacitor to limit the energy in the shock to a safe level. The transformer would produce an AC current. It hasn't worked reliably: sometimes I feel a shock, sometimes I don't, but I haven't put much work into it. There are commercial muscle-stimulation machines available for physiotherapy, so it has to be possible.

[adafruit_support_bill]

There are commercial muscle-stimulation machines available for physiotherapy, so it has to be possible.

EMS machines generally use electrodes designed for good skin conductivity - often augmented with a conductive gel. They also come with specific instructions (and operator training) on where not to attach electrodes. An electrical current capable of stimulating muscle contractions is also capable of seriously disrupting heart rhythms.

[1chicagodave]

Interesting. I've had a project going -- not very seriously -- to produce perceptible electric shocks. My idea was to charge a capacitor up to, say, 5V and discharge it through a step-up transformer. In theory you could choose the capacitor to limit the energy in the shock to a safe level. The transformer would produce an AC current. It hasn't worked reliably: sometimes I feel a shock, sometimes I don't, but I haven't put much work into it. There are commercial muscle-stimulation machines available for physiotherapy, so it has to be possible.

Lots of ways to approach that. Some a lot safer than others.

Would need some kind of oscillator circuit to start with.
Here are a couple simple versions, which may or may not be more effective.

Relaxation Oscillator

image.jpg (15.39 KiB) Viewed 552 times

...and what is appears to begin as a simple 555 buzzer circuit.

Good ole' 555 timer!

image.jpg (40.83 KiB) Viewed 552 times

**....not that I condone stun guns or shocking others with high voltage or (especially not) high current.

[adafruit_support_mike]

I just made a post on the same subject in another thread: http://forums.adafruit.com/viewtopic.ph ... 11#p235858

[Snipeye]

Thank you all very much for the replies! Lots of good info.