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TENS above the waist

13 May 2012

I posted this on FetLife in October, but figured it could use some more coverage …

Here’s the thing. We’ve all heard the “rule” that you should never play with electricity above the waist. Some people are quite vehement about it.

On the other hand, I’ve never actually heard of above-the-waist electro-play, at least not using electro-stim or TENS units, killing anyone, or even putting them in danger. Medical supply outfits routinely sell TENS (transcutaneous electronic nerve stimulation) units for pain relief, and folks put the electrodes in all sort of places, mostly well above the waist. Nobody appears to have ever died from this.

Since for the most part, when we talk of electro-play, we’re really talking about TENS units or electro-stim units that work on fundamentally the same principle, this seems to fly in the face the oft-quoted advice. Somehow, if there was, I’d expect that somewhere along the line, at least some of the vast numbers of vanillas with a TENS unit and no clue about electricity or physiology would have managed to fry themselves by now.

It seems I’m not alone, the Kinkbusters have actually tried it, placing TENS electrodes front and back of willing participants, right across the heart, cranked it up to full power and watched as they twitched and expired on the floor. Oh dear.

Actually, they didn’t. They were fine. I’m guessing they were more masochistic than me, ’cause I’ve got a fair idea how much that’s gotta hurt. But no heart fibrillations, no trouble breathing. Here’s the video:

Yeah, that myth seems pretty much busted.

But to me, there’s a difference between a safe activity and pulling a stunt that you just managed to get away with, this time, and there’s always this nagging little feeling that just because someone got away with it once, well, twice, actually make that quite a few times, things might be close to the edge and they might not always make it. Or what didn’t kill these chaps might just kill you … or, much more importantly, me. The trouble with all of the above is that the evidence is basically anecdotal.

I’d rather work with facts and measurements. Stand back! I’m going to try SCIENCE!

Now, the particular case I’m interested in is TENS stimulation of the nipples. I acquired an electro-stim device a while ago that has a pair of clips, with a copper contact on it, which accept a standard electrode lead plug. With my basic TENS unit, is hooking up the leads to my buds dangerous? Because, I might be crazy, but I’m not insane, and I’m certainly not suicidal.

The mere fact that the electro-stim device with nipple clips exists suggests that it’s probably fine … the manufacturer wouldn’t want to kill their customers, would they? But it’s also a cheap nasty device, re-purposed from a muscle stimulation device, and frankly, some stuff I’ve seen come from China scares me.

(Note that these clips are uni-polar, not the bi-polar nipple clips sold for some commercial “BDSM” stim units, which theoretically don’t pass current anywhere but through the nipples. Theoretically.)

So, let’s start from first principles.

A bit of Googling suggests that a danger of electrocution starts with a current of around 60-100 milliamps (mA) passing through the chest cavity. Now, you actually need a really tiny current (microamps) to pass through the heart itself to cause fibrillation, but its seems that to get that much current to the heart itself, a much larger current has to be passing through and around the chest cavity. Obviously, the game changes if one or more of the electrodes is inside the chest in close proximity to the heart, but …. well, let’s just say I don’t plan to test that scenario.

I won’t get too hung up on how the lethal-current through-heart number relates to the lethal-current-through-chest number, but suffice to say, lots of good authorities seem to think that over 60 mA (some say more), applied across the chest cavity e.g. in an arm-to-arm or arm-to-leg shock, carries a risk of death. So let’s just run with that.

Right, so the next question is, can a TENS unit deliver 60 mA.

The TENS 3000 (my unit, a fairly typical one), claims its pulse amplitude is “0-80 mA”


But wait, there’s more! In full, it’s “0-80 mA peak into a load of 500 ohm load each channel”. And further down, it puts the voltage at “0-40 V (Load 500 ohm)”.

Now, a power supply provides volts, not amps. Amps – current flow – is a function of voltage and resistance. Ohm’s Law, E=IR, says voltage (E, “electromotive force”) equals current (I, in amps) times resistance (in ohms). And if we plug 40 volts and 500 ohms into the formula, we do indeed get 80 mA of current.

But we have some variables. The obvious one is the voltage. It’s controlled by the amplitude knobs on the TENS unit. But more important is the resistance. Because that’s the resistance of the whole system, including the electrodes, and the body the current is passing through.

A bit more Googling, and we find that the internal resistance of a human body is fairly low, hundreds of ohms. Maybe 500 ohms for a long path (limb-to-limb). But the skin is a different story. The surface of the skin, the epidermis, is basically dead; it contains relatively little moisture and no nerves or blood vessels (these are all in the dermis below), very little to conduct electricity with.

The resistance of the skin is hard to quantify, and what few numbers are available via the web seemed to vary enormously. So there’s nothing for it but to actually break out some test gear, and a test subject.


My first reaction was simply to put the electrodes into a multimeter and test. Palm to palm (the best conductivity I found using the electrode pads – and yes you, in the cheap seats, I thought of the sweaty palm jokes long before you did!), I get around six megaohms. Nipple to nipple on the bare probes (roughly equivalent to using the clips), about three.

And let’s take a worst-case scenario: across the tongue. Somewhere around fifty kiloohms, but that varied a lot.

But I’m not satisfied. Human bodies are notoriously non-linear things, and a digital multimeter uses very low voltages to measure resistance. Worse, it tends to tweak its voltage to get better readings of linear measurements. Perhaps it’s time to step things up. Let’s get a bit more direct.

We want to measure the current in an actual shock situation. The two volts or so that the meter puts out in its resistance mode doesn’t cut it. Time to crank up the volts.

Now, I’d like to have used a real TENS unit for this, but TENS doesn’t put out a constant current. Rather, it puts out pulses; for my unit, they’re from 30 to 260 microseconds long, and at 2 to 150 Hz. That is, even at the highest frequency and the longest pulses, the power is on less than 4% of the time. A multimeter can’t measure that accurately.

The next best thing I can do is measure the actual current from a constant supply. Now I don’t have a 40 volt supply handy, but I do have a 12 volt supply.

Cutting straight to the chase, I wire up the meter, set to measure in milliamps, in series with the nipple clips and the power supply. And turn on the juice. Now this hurts a bit. It’s not like the TENS, because it’s not pulsing; it’s just a steady sting.

0.6 mA. It wobbles around a bit before settling on that number.

So, doing the arithmetic, .6 mA @ 12V gives 20 k ohms. Apply that to the 40 V maximum pulse of the TENS unit, and we get 2 mA.

About a thirtieth of the minimum current required to kill someone.

But I’m not finished. You know how you’ve always touched a 9V battery to your tongue to see if it’s good?

Well, y’know, 12V hurts more. And because it’s perpetually wet, it conducts electricity rather better. Actually, it’s a pretty good worst-case scenario for the skin resistance test.

Now you touch that 9V battery for a few moments, I’m hanging onto 12V for about a minute to make sure I have a good reading. It’s not fun, but I get a steady result, at about 8 mA. Do the arithmetic again, and we’re at 1,500 ohms. And that about agrees with the worst case numbers I’ve seen on the web.

At 40 V, we’d be looking at 26 mA. Still not enough to kill you (and this is a path length of, oh about a centimetre, not across the heart, and some of the current is actually passing through the surface saliva and not through the tongue at all), but I’m gonna guess it’ll hurt like Hell. I’ll point out at this stage that the instructions for the TENS unit quite explicitly state that one should not place electrodes in the mouth.

Wetting the skin makes a small difference. I suspect that if you pruned out in a warm bath of salt water, you might drop a digit off the dry resistance. But short of stabbing probes into your flesh, you’re not going to get a heart-stopping current from a TENS unit, no matter where you put the electrodes. And it’s probably going to get too painful to take before that happens.

Further, for the nipples, or most other reasonable TENS applications (both therapeutic and play), very little current would actually pass through the heart even if there was 60+ mA involved. The bulk of the current will be in the flesh just below the skin, taking the shortest path through the best conductor. Below that flesh is a mess of rib cage, sternum and connective tissue, or rather higher resistance.

Now, before I close, note that I’ve tested only certain cases. The TENS unit instructions contain several safety don’ts, which I’ll paraphrase here:

  • Don’t use if you suspect heart disease;
  • Don’t use when pregnant;
  • Don’t use with pacemakers and other implanted electronic devices;
  • Don’t put electrodes on the throat, over the eyes, in the mouth or internally;

I’d endorse these; most of them have good reason, even if it’s “nobody’s tested this fully, so we can’t say it’s safe”. But they’re a heck of a long way from a blanket ban on all play above the waist!

And finally, the above is all based around the specifications of one device. Check the specifications of your device before applying the conclusions presented above. And of course it your device is not a TENS unit, all bets are off!

11 Comments leave one →
  1. 27 May 2012 4:50 pm

    Excellent analysis, the best I’ve seen so far. I’m especially impressed with your calculations and your study methods – both are very convincing.
    BTW, I’m a bondage video producer and Rigger, but I’m also an Electrical Contractor. I never bought the idea that a electrosex unit above the waist could stop your heart; if it could, people would be getting killed setting up stereos and working on cars, not just using TENS units. A reality check for me was that my PES unit works nicely on a 9v battery. Except under freak circumstances, there just isn’t enough energy in one to do any damage.
    I called the manufacturer of my box and talked to one of their technicians; he’d never heard of anyone getting injured by one of theirs or any other type.
    On the other hand, a ProDomme I know asked me to look at her “electric chair”, which wasn’t working. It was a chair made of 4×4’s, with strategically placed copper plates and straps…. fed by a great big Variac plugged into a wall socket. A Variac is a variable transformer; this one would put out from 10 to 120 volts at 20 amps! That can burn you or kill you quite nicely, thank you very much. Luckily the idiot who made it inadvertently wired it to short out, which is why it didn’t work. I took the Variac with me, and she threw the chair out.
    Do you mind if I share your information on Fetlife, with attribution, of course?

    • 27 May 2012 10:59 pm

      Eeep. Was the chair not salvageable?

      Re not enough energy in a 9V battery: you’d be surprised; here’s more than enough energy in there. It’s how you harness it that’s the key, hence the line of enquiry. For example, to deliver 100 mA @ 180 Vac, you need the battery to provide 2 A @ 9Vdc (plus losses through the inverter & transformer). Dry cells might have trouble with internal resistance but an alkaline cell could probably do it.

      Similarly, your variac can be made “safe” by simply putting a resistance in series with it; 6 kiloohms would get 120V down to a “safe-ish” 20 mA in a dead short.

      • 29 May 2012 7:20 am

        Good points, Ruru. I made her throw it away; she was a former sub of mine. It was pretty clear to me that, at age 22, she shouldn’t be playing with anything more than a TENS unit.
        This was around twenty years ago; she’s now a highly respected and accomplished Domme 🙂

  2. jacko permalink
    31 May 2012 9:36 am

    I think the resistance of peoples bodies varies greatly there are plenty of cases of people dying from there first electric shock, yet I am an electrician and have been for 32years and have had many electric shocks from the mains and suffered no ill effects and in europe its 230v and 400v and it bloody hurts.

    • 31 May 2012 2:05 pm

      I think 230V mains supply is “safer” than 110V. Both can kill, but 230V hurts a lot more and you’re consequently much less likely to repeat whatever stupid thing you were doing to get shocked …

      I’ve taken my fair share of 230V hits (NZ is 230V single phase / 400V three phase as well), from faulty equipment, carelessness etc.

      Mostly, though, shock vs kill is much less a question of resistance than of circumstances, in particular, getting into a situation where current is passing through the body. I don’t know about you, but I was always told that if you’re working on something particularly nasty, keep one hand in your pocket, in an insulating glove or at least safely away from anything that might provide a path to earth. Touching a 230V phase with one hand will hurt, but that’s all; grounding it with both in such a way that you can’t let go will kill you for sure.

      With TENS and similar rigs, you’re setting things up so that the current is passing through the body and letting go isn’t an option. So now, body & skin resistance does count, and that’s what I’m addressing in the article above.

      Also note that TENS voltages top out at about 40V. That’s a lot less than 230V (or even 110V). The higher voltages also break down the resistance of the skin, presenting higher currents through the relatively low resistance flesh below. TENS voltages won’t do that.

  3. EnigmaPOJ permalink
    24 September 2012 11:37 am

    Remember it’s the amps that kills, not the voltage. When I was electrical engineering professors always stated the following about amperage across the heart:

    500 and 1000 and 5000 ma ( 5 amps ), things get fried and death most likely for anyone.

    Just because you touch a 20 amp circuit doesn’t mean all 20 amps is going to go through the heart, it usually doe not. Electricity takes the path of least resistance and the heart isn’t usually isn’t in that path unless you put the electrodes in just the right place in the 11 and 5 O’clock position of where the hearts is. (Where you put the paddles/electrodes on a defibrillator.)

    Since most TENS units put out less than 100 ma ( usually they max out at 80 ma), it should be safe for most people. However I would not use on someone with a pacemaker as it could disrupt the pacemaker while in use. Today’s pacemakers can take a lot of punishment (my step father has one) and he doesn’t even have to worry about microwave ovens anymore because they have improved so much.

    • 24 September 2012 12:14 pm

      You need a hell of a lot less than 5A to kill someone. US mains at 110V, can kill. At ~ 500 ohms internal body resistance (that’s assuming the voltage has burned through the high resistance skin), that’s still only a couple of hundred milliamps. It’s just a question of placing yourself across it and not letting go. Holding on to a phase with one hand and a drainpipe with the other will do it. The ~230 V used in the civilised world is even more effective. You won’t even pop a fuse. That’s why RCDs are such a good idea.

  4. Paul permalink
    25 November 2013 9:28 am

    Do note that making proper contact does significantly increase the effectiveness of stimulation. I use tubular carbon-rubber electrodes, and using an electrolyte solution (eg shampoo, ultrasound gel) increases the effectiveness by probably an order of magnitude.

    My sense has always been that the risk of fibrillation is overstated. I wouldn’t stim across the chest (eg hand to hand or between nipples) but I don’t think shock collars on the neck or stim above the waist is a particular concern otherwise.

  5. jjim permalink
    18 January 2015 3:05 am

    A few years (decades?) ago I did some research on this. It’s more complex than just the amperage. A researcher managed to kill himself despite being healthy. He did this with EKG monitoring and a pulse generator, most likely with a PLL that could link the pulse phase with the heart rhythm – that’s what can do you in, with a relatively small current.

    OK, imagine a graph with a black hole in the middle. The y axis is the intensity of the current; the x axis is the phase difference (in degrees, whatever) between your pulse generator and your heart rhythm. Now, as you increase the amplitude at some point away from the black hole, at first there’s no change in the heart response; then the pulse might be slightly advanced or delayed with more current. At a much higher current, the pulse is reset by the jolt, but still no problem other than some discomfort from the current.

    But if you start increasing the current in the phase locked pulse generator just below the black hole, the pulse will either lag or advance from the regular pulse rate as the current increases. But here’s the literal killer – if you have just the right current, at just the right phase, the heart has been either advancing or lagging the pulse rate each pulse; but inside the black hole, the heart is caught in the dilemma of not knowing whether to advance or lag the pulse rate; that’s where fibrillation sets in. If the pulse is powerful enough so the current is above the danger zone, the current will just reset the normal pulse rhythm from that jolt. But if it is weaker and inside the black hole of the graph, the normal pulse rate will try advancing and lagging the normal pulse at the same time, and it will get disorganized fatally. A healthy heart can make that black hole arbitrarily small, but that fatal current/phase combo will still be there. (I don’t know how long the PLL pulse generator must stay in the black hole danger zone for it to be fatal; it’s probably more than a single pulse.)

  6. Sir Roper permalink
    24 October 2017 2:49 pm

    As an one with a passion for electronics since age 10, with IBM at age 18, a systems engineer for 20 years, a broadcast engineer for 8 yrs, and a test instruments design engineer for 8 years and an avid rope bondage enthusiast since I tied up my babysitter at age 7 and having done a great deal of thinking about the use of electricity for fun…I have a tens unit… I have to say, I never expected to find such an intelligent discussion of this subject. but then, everything…anythings on the web… but I say “great job” to the site owner and all commenters.


  1. A TENS On The Nipples: Safe? – ElectroSex Blog

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