My Laptop Bit Me – The Shocking Truth (2012) | Hacker News Reader

My Laptop Bit Me – The Shocking Truth (2012)

enclydion.blogspot.com

136 pointstomduncalf116 comments

This happened to me in around 2005. I was constantly getting shocked when I opened my MacBook. So I took it the Apple store in Berkeley and they harrumphed and said it was within spec. Still getting shocked. So I took a multimeter and measured the current and showed that to them. They harrumphed again and said that service would look at it and probably wouldn't fix it. But they fixed it.

Yeah their "genius bar" left a lot to be desired, I switched away for that reason. At first they were great, but over the years the one I went to just stopped really trying and instead shifted more to sales.

Service did fix it. To be fair, it was the only MacBook of mine that's had that problem. I've had many.

I hate that there is no literal "genius bar" anymore - now you have to fight for table space like it's a SoMa coffee shop.

Every Apple store I've been to in the last five years seem to have been designed for half the number of occupants they actually have.

I mean, it's not surprising why: they were likely designed before Apple was as popular as it is today.

I've noticed that even with an earthed power supply I still have the problem with the newer USB-C MacBooks. I find it rather uncomfortable on my wrists.

A MacBook I had quite a few years ago had a cracked chassis - touching that when using a non-earthed power supply was enough to be a little bit painful.

I have the same problem with a bog-standard Dell laptop power supply. The safety ground (earth) lead is bonded to neutral way the hell back at the meter so there's too much inductance in the lead and through the whole house to do much good other than prevent electrocution.

Can't you simply unplug this connection and install a proper earth at your place? That's what I did (literally: huge copper bar buried) and a lot of stuff (including the shower, which in my country is electrically heated) stopped giving me tingles.

There's an 8 foot long copper rod as the earth ground now. Replacing the existing connection would be nasty, the power company would have to come out to pull the meter (it's sealed) to get at the bonding strap inside the box and it's doubtful they'd reenergize the place without a visible bond.

That sounds smart, though I can't imagine a huge copper bar came cheap. You can get something for as little as $17 off Amazon, and maybe cheaper if you look harder: https://www.amazon.com/Skywalker-Signature-Ground-Rod-4ft/dp...

Grounding rods are generally copper clad steel. In the US, proper ones are 8ft. $13 at Home Depot. An electrician can either measure the actual impedance or put in two rods with some spacing, so they're often just used in pairs.

Back when Radio Shack was closing I put the damper on some guy who was going to buy all the grounding rods thinking he'd scrap the copper. I did him the favor of disappointing him before he spent his money.

Does not have to be copper. I've done several of these using galvanized steel hammered into the ground. We'd hammer in rods of 2 meters length until the resistance was low enough (around 1600 ohms Iirc). This would ensure hpfi tripped below 50mA

Be very careful about this. Grounding isn't always as easy as hammering in a spike. Some soils don't conduct properly, something that can change throughout the year as water tables move.

A few US soldiers in Iraq were wounded in showers because while the electrical system was not properly ground, the shower drains were.

We used to frequently have problems with the electric fences on our farm for this same reason. Once every few weeks I pour a 5 gallon pail of water over the grounding rod to keep the fence at 7,000V. Works like a charm. This is particularly problematic where soil is a shale/gravel mix and drains quickly leaving little moisture. Grounding requires moisture for maximum conductivity. Good grounding is also required to complete the electrical circuit when you touch the fence.

Salty water (or acidic, or basic water) would be even more conductive, no?

And the salt would reduce evaporation (and remain until it rains) until next time.

Would probably kill any crops, which will help retain even more moisture.

I hadn't considered this, but yes, now that you mention it, given that salt water is more conductive, it would perhaps be more effective.

My fences appear to provide maximum output (on a standard livestock electric fence tester) with our regular well water, so it hadn't occurred to me to give this any further thought.

There are already sufficients ions in the soil to conduct well.

The question is, does it conduct well enough? And that depends on soil type and moisture level. When it doesn't, even 0.1% salt in the soil moisture has 1/10th the resistance:

https://www.newark.com/pdfs/techarticles/megger/Tech_Tips.pd... (top-right).

Over time, whatever ions are in the soil will get washed away, so you need to keep re-adding, even if you started off with ion rich soil (e.g. from backfilling).

Have you actually checked the ground for continuity? IN my house, I found that many of the upstairs outlets (wired with BX) had their grounds bonded to the water pipes in my house, instead of run directly to the box, and then the water pipe was bonded to the box down near the service entrance.

Unfortunately, there was no ground continuity because at some point a pipe segment had been replaced with PVC instead of copper and the continuity ended. Bonding grounds to pipes was very common in older houses and is a common source of bad ground loops and electrical noise.

>> a pipe segment had been replaced with PVC instead of copper

Which is why when you do that you are supposed to always install a wire to jump over the now non-conductive section of pipe.

Exactly what I did. I’m not sure the original homeowner knew that it mattered.

I first noticed the issue with a stepper motor project I was working on. It was very interesting to hear the reduction in audible noise from the motors when the grounding was fixed.

Also if current runs over pipes, there might be more corrosion when different kinds of metal meet. You should never run ground over pipes, but instead use a dedicated copper wire

This is a true story. One night, I went down into my basement and heard a snapping sound, and looked to see sparking between a 12-14G copper ground wire (from somewhere) and my water supply pipe. It turns out that my 1952-build house did NOT have a ground/earth for the panel, and a squirrel had chewed all but the last few strands of the neutral coming from the power pole. Most of the return from the house was going through this piddly ground strap, and it was not happy.

I called the power company, and they were kind enough to install an new neutral almost immediately (perhaps at night). I then called an electrician, who grounded my panel.

I am still amazed that my refrigerators and ovens worked, and wonder what would have happened if I had not heard the snapping sound.

> Have you actually checked the ground for continuity?

No, not in a reliable way. I have continuity between neutral and ground at the socket but I can't tell if what I'm seeing is some bozo's swamp "bonding" behind one of the branch outlets or the actual bonding near the service entrance.

This is the standard everywhere in Europe, with separated earth and neutral wires which are connected and grounded somewhere farther. It is done for a purpose and not a problem when done properly. The resistance nor inductance is never enough to allow so high potential, even at kHz frequencies of switching power supplies. So this indicates a problem on earth wire that should be fixed by a professional, not by blindly adding some makeshift earthing.

It's the standard in North America too, neutral and ground are bonded at the panel and can't be connected anywhere closer than that (which would be referred to as a 'bootleg ground' and could create electrocution risks if the wiring is wrong)

Same for the back of my iPad Pro at times, too. I appreciate this post – thought I was crazy!

Mildly off-topic: is "earthed" a European-ism? I've only ever heard "grounded" until reading through this article and thread.

It's certainly British English.

>Mildly off-topic: is "earthed" a European-ism?

Yes. We say "grounded" in the US English, but in UK English it's usually called "earthed".

Grounded means no tv or video games for 2 weeks.

I’ve done enough reading for electrical wiring for both small electronics and electrical power that I’ve seen both terms frequently enough that neither seems out of place to me.

Maybe also a translation thing, in German "grounding" is translated to "erden" which means "putting into or connecting to the ground", but "Erde" is also the substantive meaning "earth".

Words take on a range of meaning. "ground" and "earth" have overlapping meanings.

Sure. In English though it's fine to refer to e.g. the street as "ground", like when you drop your ice cream outside. In German, "Grund" would be something like the ground of a lake, your ice cream would drop on the "Erde". So they have the same meaning but in the overlapping area English is biased towards ground and German towards earth. Or something like that.

British English - the author is Australian.

In a previous life, we distinguished between ground and earth, where "ground" was a sloppy term to describe a circuit's zero reference, and "earth" was a precise term that described the zero-current safety path to the dirt.

The team was highly international, with a strong European influence, so that could also have been part of it.

In the UK, at least, that distinction is still used.

GND is the symbol for 0V in circuits. Earth is, as you say, the safety path to actual ground. It's the 3rd pin on domestic mains plugs, and you can't call something earthed if it doesn't connect to the safety path.

But I'm pretty sure we use "virtual earth" for op-amps :-)

In Australia, Earth. Also Earth is not an uncommon term for ground or soil.

"grounded", which is the US usage, derives from the phrase "tied to earth ground". This derived from the fact that an "earth ground" is literally connected to "the ground" ("ground" as in "the surface of the Earth" [1]) because an "earth ground" is a six foot copper pole sunk underground to which the "ground" buss bar in an electrical distribution panel is tied.

So in the US, it seems we shortened "tied to earth ground" to "grounded" for common usage while in the UK the shortened version became "earthed" [2].

[1] https://www.dictionary.com/browse/ground - noun definition #1 or #2

[2] https://dictionary.cambridge.org/us/dictionary/english/earth...

No, it's just English. However "grounded" is an Americanism.

The real question is, if the common wisdom is to ground the chassis when possible, and even the induced voltage on the chassis is harmless, they are seen as a widely recognized annoyance. So, my (Question 1) then why does the hardware designers keep using ungrounded design in the first place? Just because they think the output through a isolated transformer is safe enough (also can meet safety regulations), so they want to then omitting the Protective Earthing to simply make the power supply smaller and they think it's okay to give the users some small shocks? Or it's something else?

And here's another question I don't understand. When a piece of electronics don't have a Protective Grounding connection, the common explanation is: the low voltage is created by a SMPS, and an isolation transformer at the output side of the SMPS makes the voltage no longer being Earth-referenced, so in the worst possibly scenario, if a grounded person touches the "hot" output wire, nothing would happen. But if you ground the chassis to the Protective Ground (often the ground of the PCB is connected to the chassis), the output becomes Earth-referenced again and loses the protection of isolation. This is why an isolation transformer has a unconnected Protective Ground at its output side, and many SMPS-based appliances don't use the Protective Ground.

So my Question 2, according to the common wisdom and many regulations, most appliances should be grounded, but from the principle of isolated power supply, it should not be grounded. And in real life, we clearly see lots of laptops use DC power supply without the ground connector, and others with the ground connector. And to further complicated the issue, some DC power supplies only use the ground internally for the EMI filter circuity and/or its own enclosure, but the DC output itself is isolated and is not ground referenced. Then how can an isolated power supply with the ground plug help stopping the induced voltage on a laptop's enclosure, if the output is isolated? Something related to the leakage current of the X/Y capacitors? It seems there's lots of inconsistency here. Just why?

> So, my (Question 1) then why does the hardware designers keep using ungrounded design in the first place?

Ungrounded sockets are still very common (just off the top of my head, in Japan, Philippines, Australia, all through Europe, India...). Even as building codes change it takes many decades for the housing tock to upgrade. Even when the code requires upgrades to commercial buildings it rarely will of residential.

If the leakage is harmless (or "harmless) why risk the user buying a product, getting home, and then being unable to use it. The OOBE is terrible and possibly fatal.

This is also why the "international travel kit" for Apple power supplies contains non-grounded plugs.

The authors final and correct point about Apple is fortunately now obsolete as since it was written Apple has switched to standard Type C connectors. On the other hand they no longer ship grounded connectors by default (in the USA at least).

They do ship grounded connectors still, but it is underneath the molded plastic piece at the bottom of the box which is hard to get out.

As far as I know Apple does not ship a three-iron plug in the USA except when attached to a cord. They do in some places like the UK.

Apple plugs in the UK have three pins because it's necessary to operate the safety slider in UK sockets.

But (for laptops) the earth pin is not connected internally.

(rummages through Apple travel adaptors): holy cow you're right!

That's a false rumor. https://forums.macrumors.com/threads/macbook-pro-16-17-comes...

Hmm. Thanks!

Per the common product safety standards (national standards based on IEC 60950-1, 60335-x, 62368-x), Class I and Class II construction are defined per the level and type of protection from shock for 'grounded' and floating enclosures, respectively.

Per your SMPS reference, the output reference depends on the design intent and intended end-use environment. Depending on the scoped standard, outputs greater than 50Vdc will require a minimum separation from the both exposed dead metal and stuff referenced to an earthing terminal. Where the output is considered safe to to touch, there are only functional spacings required. Also, Class II construction is, in fact, not intended to be 'grounded', and must not be a hazard for a fault condition where the enclosure touches either mains voltage or metal referenced to an earthing terminal.

Class II construction requirements are supposed to mitigate a single fault condition associated with seperation from and contact with a hazardous voltage or power source.

Most potentials between the user and ground are due to current flow through the y caps (noise filter caps rated to between a hazardous voltage level and the user). Touch current, depending on the scoped standard and category and class of equipment is typically limited to less to 5mA (some equipment is allowed 25mA). Class II equipment is typically limited to 250uA. Given the assumed human-body models in IEC60990, the voltage at max allowed current leakage would range from imperceptible to noticable but not effectual.

Shock hazards can exist from improper construction or improper installation and of equipment.

I have the same problem with my Asus Vivobook. It has aluminimum body, and sometimes can be quite uncomfortable on my wrists as I get the constant buzzing feeling. I've been wondering if I could just buy a plastic skin that would protect me, because where I live, I can't really change the plugs.

A coat of lacquer should do it?

Or a properly earthed power supply, maybe?

> because where I live, I can't really change the plugs.

In most of the world "changing the plugs" isn't really a thing, the problem is the design of the power supply (hence my comment.)

To clarify: Floating switchmode power supplies that aren't isolated from a separately earthed conductive shell are a bad thing.

It's not just an issue for humans. I often have the problem that touching my single board computer (ODROID-UX4) or plugging another mains powered device into it like a screen zaps it and causes it to fault and reset.

I wonder if this is because it has a Chinese wall wort power supply with a UK adapter. Particularly, the Chinese two prong plug is symmetrical and fits the UK adapter in two orientations, so live and neutral are not differentiated.

>Chinese wall wort power supply

What did you expect?

Does this ever get bad enough to feel without touching something else to directly complete the circuit?

I would predictably get this when using laptop (on lap) and resting my arm on a metal heater next to me. I ended up returning a few AC adapters because the leakage was too damn high, and eventually they offered me a three prong version that came with many more regulatory marks.

The problem with two prong devices is that a designer has to assume either wire could be hot, because it could be plugged in backwards. I've got to wonder if a change in the regulations that would allow for a single cap to the probable neutral could solve this. It would double the leakage current if the thing were actually plugged in backwards, but as long as it was just more uncomfortable rather than dangerous this would be a win.

Also there are a few handwavey things at the bottom of the post that just leave me scratching my head:

> Even though the MagSafe power supply itself is not connected to the mains earth, there is just enough inductance leakage for the floating charge to dissipate through the plastic sheath of the mains cable.

There could be something to what is being said, but if there is he's not describing it well.

> It's worth noting that the fuzzy-electronics effect can be felt if you use an earthed power point but the power point's Active and Neutral are wired back to front

That's an odd diagnosis, because three prong means the output is being directly grounded. Instead, I would infer that the ground (EGC) was disconnected (like say an old home where someone improperly changed two prong to three prong outlets when remodeling).

I felt this effect for the first time when I was living in Israel for a few months. I couldn't rest my wrists on my MBA while it was plugged in because of how painful it was. People said the power was "dirtier" over there than in the US (lots of voltage spikes? rougher waveform? not sure) so maybe that made it worse.

Assuming you're coming from North America, I found across Europe when my laptop was plugged into 240V I would get this, while 120V in North America was fine. It would also vary depending on the power draw - when the battery was recharging it would be worse (I think).

I ended up unplugging and running off battery as much as possible, and eventually buying a smallish bluetooth keyboard and mouse to take on trips.

> It's worth noting that the fuzzy-electronics effect can be felt if you use an earthed power point but the power point's Active and Neutral are wired back to front.

That's an interesting issue, since in continential Europe (and a lot of the rest of the world) the plugs are symmetrical and don't distuingish between active and neutral. I guess if this happens to me with a three-pronged plug I should try flipping it.

>That's an interesting issue, since in continential Europe (and a lot of the rest of the world) the plugs are symmetrical and don't distinguish between active and neutral.

It really doesn't matter much with A/C since the voltage is always flip flopping. You're basically a bird on a wire at all times but that wire is the earth itself. I can't think of any situation where a properly manufactured device would care which contact is neutral and which one is power. Ground is (in theory) always separate from neutral on the device (it should go without saying that it's separate from the line otherwise you have a short to ground). Plugs in the US used to be symmetrical too.

Edit: Since apparently I'm Wrong(TM) does anyone want to tell me why?

(1) Your advice could kill people, and (2) it's not reasonable to claim that decades of expensive electrical mains and appliance design&manufacturing was done for no benefit.

The ground wire connects to non-electrified portion of the device, as a protection against accidental electrification.

Neutral closes the mains circuit also is grounded, protecting the electrified portion against accidental activation.

https://en.wikipedia.org/wiki/Ground_and_neutral

That article also has a section about how mechanized-farm cow milk production is harmed by the issue discussed in the OP

Of course you don't want to use the ground as your neutral. In normal wiring it's not designed to do that job so it sucks at it. I'm talking about the polarity of the line and the load as it relates to the device being powered. Your comment seems like a complete and total non-sequitur to that. I'm talking about a directional plug here.

> Your advice could kill people,

I am not giving any advice. I'm saying that unless you're doing something complex involving the neutral and ground no technical reason the neutral and the hot contacts on any given device are not interchangeable because the electrons are going both directions anyway.

> it's not reasonable to claim that decades of expensive electrical mains and appliance design&manufacturing was done for no benefit.

You can still get devices in 2019 that are not grounded (common) and do not have a directional plug (rare).

>Neutral closes the mains circuit also is grounded, protecting the electrified portion against accidental activation.

How is this related to what I said? Yes neutral and ground are both "grounded to the ground" at some point (usually the panel) but the device being plugged in doesn't know the difference between the neutral and the live wire because its getting its electrons from both (because AC).

> and do not have a directional plug (rare).

https://upload.wikimedia.org/wikipedia/commons/thumb/5/50/Sc...

What would a directional plug for this socket look like?

I don't know. A non-directional/non-polarized plug would just omit the features that engage the key-ways on the side enabling you to plug it in whichever way you want. If you want to make it directional/polarized just engage the key-ways so the user can only plug it in one way.

In North America we have these[1] for things that don't have a metal case and on cheaper devices both blades are often the same size allowing you to plug it into an outlet whichever way you want.

[1]https://cdn.sparkfun.com/assets/5/1/0/d/c/51154c1cce395f903d...

What parent is getting at is that Socket Type F "Schuko", one of the most popular socket types, is completely symmetrical and inherently non-polarized. Since any plug compatible with Schuko is non-directional calling non-directional plugs rare is factually wrong (if we talk globally). It also proves your point that the difference between life and neutral largely doesn't matter, since in about half the world wall sockets don't care about the difference.

> I'm saying that unless you're doing something complex involving the neutral and ground no technical reason the neutral and the hot contacts on any given device are not interchangeable because the electrons are going both directions anyway.

They are not interchangable for safety, electric shock, or EMC purposes, because the AC voltage range at neutral and hot contacts are very different. This is when the voltage is measured relative to the nearby environment.

Roughly speaking, the neutral AC voltage may oscillate around +/-2V (that's all), relative to the surrounding environment.[] If it's more than that you probably have a fault.

Whereas the hot AC voltage will oscillate around the full range you'd expect (~110V RMS or ~230V RMS depending on country).

This makes them very different, with regard to human safety, other safety (such as sparking against an earthed pipe, causing fire, contact with water), and current flow to the environment via capacitive coupling.

[] - Neutral is bonded to ground somewhere, but not at the mains outlet. The reason it's not zero and a small voltage appears, is because all the devices plugged in closer than the neutral-to-earth bond contribute a small "pull" to the neutral voltage, competing with the bonded voltage.

I agree that in a device without exposed metal and with a two-pronged plug it doesn't matter. And those devices extremely common at least in Europe.

It's mostly problematic if you make assumptions around knowing which pin in neutral that turn out to be wrong: for example on a lamp socket you could put the exposed part on Neutral, making it safe to touch. That becomes dangerous if you switch Neutral and Life. If you assume you don't know which is neutral you obviously wouldn't design it that way and protect any metal surface with some isolator (plastic) or ground it.

> Since apparently I'm Wrong(TM) does anyone want to tell me why?

I think because some devices are designed such that incidental contact with neutral (before the load) is possible under normal circumstances, which means (if the internal circuit in the device is not complete) you could get shocked if hot and neutral are swapped.

An example of such a device is a plug-in light fixture with a screw-in bulb. You might easily touch the edge or side of the socket while there is no bulb in there. You are much less likely to touch the contact deep within the socket. So the fixture is wired to make the socket neutral and the contact hot.

I wonder is this is related to an issue with my Surface Book: when it’s plugged in to some (but not many) power outlets, the trackpad becomes unusable (the cursor skips all over the screen when you touch it). I’ve noticed it in a couple of hotels, and unplugging it and using battery eliminates the problem. I wonder if it’s related to this surface (pun not intended) charge caused by bad grounding?

Are there alternative solutions to this problem, that are not interesting for industry, but feasible for hackers?

E.g.: remove those two capacitors that bridge the primary and secondary sides of the power supply. Tingle is now gone, but the supply is now emitting a lot of EMF noise. How about arresting that with some bulky ol' ferrite cores?

That's quite interesting! I always wondered why there was a "tingliness" when I ran my fingers lightly over the top of my laptop when it was plugged in, good to know.

It is a little concerning that this was with my Asus Zenbook, which comes with a 3-prong power adapter...!

Are your outlets properly grounded?

Electric exposure is such a new phenomenon in terms of human evolution... like, humans have had their hands on small charged devices for like less than 100 years.

I wonder if an overweight person feels less of the electricity since they have more fat shielding their nervous system?

We've been exposed to static electricity through all of our history.

i think a hand rubbing against a wool sweater making a little shock is different than having a laptop over my nuts for 10 hours a day!

I've had this on lots of laptops, but the worst was a thinkpad, whose only exposed metal was a little fingerprint reader that lined up perfectly with the softest, most sensitive skin of my wrist. I hated the little shocks from that thing.

I had the same experience with a T61 I owned, and used to just tape a bit of plastic foil over the reader (I wasn't using it).

I never felt a buzz through my laptops when I lived in the US, but I feel it fairly often in Netherlands.

What is really strange is that occasionally I could feel the buzz while gently moving my fingertips across my girlfriend's shoulder while in bed. It was not an imagined sensation - it was exactly like with the laptop. We were on a waterbed, but I don't think that could have anything to do with it. The laptop mystery is solved, but this one is still a curious mystery.

I had (still have lying around) a Toshiba Portege purchased way back in 2012. It had quite sharp edges that gave out a shock whenever my elbows grazed them. The shock was mild but very discomforting and made me very conscious when using the laptop. Over time i discovered that using a 3 pin plug avoided the shock. In 2015 i switched to a macbook pro which also has this issue. Thanks to this article i know whats happening.

I've felt that uncomfortable tingling and occasional shocks on a number of laptops, be they metal chassis (Macbook) or plastic. Some friends report being zapped by their Macbooks.

The weirdest for me was my first laptop. I kept getting shocks from the palm rest, even though it was all plastic and presumably a good insulator.

I didn't understand how a shock could reach me through solid plastic.

> It's current that kills, not volts.

I wish people wouldn't say that, it's a complete mischaracterisation of how voltage and current work.

When it comes to lethality, time is also an important factor. A very short burst of high current is not lethal.

So if you really want to be correct, it's electrical charge that kills.

edit: typo

If you take time into account then it's power dissipated that matters. But again, with high-frequency AC the skin effect comes into play and you also probably won't die as easily as you would with same power being dissipated by DC going trough you. It's simply not as simple as just one sentence.

No, this isn't true either. The way that most people die of electrocution is from heart fibrillation, not from having their arms blown off by extreme voltage and current levels. It doesn't take much current to cause your heart to fibrillate; only about 100mA across your heart. So getting a shock that conducts that much current through your foot or hand probably won't hurt you, but getting a shock that conducts that current across your heart can. In short, it's more complicated than anything being said here.

Even if the heart muscle doesn't kill you, you can still die from the chemical imbalance caused by subjecting to your whole body to electrolysis. So if you got shocked, visit a hospital immediately! You can still die hours later.

Citation needed. We were taught about electrical safety and its effect on the human body in college EE classes, and there was nothing said of this.

Fair enough. I've read in an interview of a hospital staff doctor, not sure if I can dig up the source.

Edit: so the way this works if current is flowing through your body your blood is undergoing electrolysis, and as a consequence your Kalium balance can get disturbed. This can result in severe heart rythm issues, even hours after the shock. A doctor can test this and fix it with an infusion.

Not my original source, but says the same. Should be understandable with Google Translate: https://derstandard.at/1343744823640/Wenn-scheinbar-harmlose...

And it apparently only takes 10mA before you can't physically let go of AC, thus screwing you anyway. Imagine being stuck there, slowly electrocuted to death. bigclivedotcom did a video where he actually tests this ... https://www.youtube.com/watch?v=-5R-KBa18ME

EDIT: Perhaps I should make clear: he quite literally runs 240V mains from one hand to the other, slowly reducing the series resistors until he can't physically let go anymore (at a bit above 10mA for him). Live, on camera. Neat! (He doesn't die; saved by a safety foot pedal).

(Also check out his other videos, including the recent ones about the vintage household appliance that cooks hot dogs in 60 seconds by running 120V directly through them!)

He is right though - time is important. That's why RCDs work.

The voltage/current distinction does become important when your body forms one branch of a current divider, though that's only one approach to electrical safety, and others certainly do work by just reducing the voltage across the body.

Electrocution is a complex issue, so it's not really true to say that it's the voltage, current, power or energy that kills you. A sufficiently large amount of energy will definitely kill you, but for everything else the answer is "it depends".

Right, it is the current that is delivered through the body that is an issue. For example, if you have a 12 volt power source that has the potential to deliver 50 billion amps, it isn't going to deliver any more amps across your heart than a normal 12 volt battery. That is because your skin has resistance, and Ohm's law comes into play. Things change of course if it is hooked up to needles that is poked through you though, of course.

It's like "acceleration is from torque not power". Technically true but unhelpful.

Would you like to try a 150kV power supply that I have laying around here?

If it can only deliver 1nA, then yeah.. Won't hurt a fly

Yeah depends on its output impedance.

When I took my MacBook to France I noticed this too. It was enough to make me really nervous. Never noticed the tingly feeling in the US.

So that's why I always have this tingly feeling under my fingertips whenever I use my macbook! I always wondered what that was.

Note that using an Apple laptop charger with its included three-prong charger cord will provide a grounded charge (no buzz), as opposed to Apple’s or any two-prong connector (or a third-party three-prong that’s missing the female grounding connector inside the charger-side plug).

I have experienced this in a very weird but completely reproducible manner. My Logitech G27 steering wheel has a power plug to run the force feedback system. If you connect the peripheral to power but not to the computer, touching the metal pedals causes strong burning sensations.

I had an old Acer laptop, the C710 i think, where the touchpad would only work if you grounded it. Only the whole chassis was plastic so you could only operate it with one hand because the other had to touching the little band of metal around the VGA port.

When my old macbook air is plugged in I can feel the electricity in my palms resting on the aluminum while typing. It was kind of like those old prank shock pens, but less intense

The description of how SMPS works in thei article is shockingly inaccurate!

  > To simplify, an SMPS essentially
  > takes the AC input and turns it on
  > and off very quickly (between 10,000
  > and 20,000 times per second), with
  > the output voltage being determined
  > by the duty cycle - the amount of
  > time it is on for each flipflop. The
  > shorter it is on, the lower the
  > voltage. This is fed into regulators
  > and capacitors to produce a stable
  > AC voltage, which is then converted
  > into DC.

Literally no part of that is accurate. SMPSs generally rectify first,then PWM, then smooth

Right. But not the real issue. See [1][2]. Most switching power supplies have a small capacitor between the AC line and output sides of the transformer, to provide a somewhat tenuous path to ground for RF noise on the output side. That's a fundamentally bad idea, but cheap. Better approaches involve either a real ground, with a 3-prong plug, or some new designs which handle RF noise in a way that doesn't need a path to ground.[3] Here's a patent (in Chinese) for a solution without a bypass capacitor.[4]

[1] https://i.stack.imgur.com/fV15S.png [2] https://electronics.stackexchange.com/questions/216959/what-... [3] https://ieeexplore.ieee.org/document/7488992 [4] https://patents.google.com/patent/CN202818110U/en

I thought this would be about how an XPS 13 will literally bite you with its hinge. I got a few blisters having my finger in the wrong place when I open the lid.

I've noticed this a few times - it's usually what e when a stray Lightning/USB cable is touching another part of my body.

I had this with a Dell XPS in India but it was connected somehow to the power supply. Maybe some voltage crept to the ground wire. Dunno.

I already noticed that I didn't have this with an earthed (grounded) wall socket, very nice to finally see the explanation!

VGA external monitors were also susceptible to this, resulting in a wavy interference pattern.

2012.

The unchanging laws of electricity still make this article...

...current

You have my upvote for that electric witticism.

This isn't about the laws of electricity but about how the power supply is designed. I was surprised recently when my Mac-using colleague needed a three-pronged extension cord. I don't carry those around in my backpack because everything I need is two-pronged. I thought it was silly that Apple would force this on their users. With a regular transformer/diode bridge/capacitor power supply this isn't needed.

The traditional use of a ground-plug in these situations is to protected the user against electric shock should "hot" a wire get loose and touch the metal case. But when the voltage is dropped to non-lethal amounts (or if you have a plastic case) this is unnecessary. In fact, most "third wires" don't even make it to the device- they terminate in the transformer box. So the Mac plug was truly a bit perplexing.

But now I know why.

Doesn't look like the laws of physics have changed much since 2012, have they?

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