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How can I avoid my MacBook Pro giving me minor shocks? (stackexchange.com)
193 points by luu on Nov 14, 2016 | hide | past | favorite | 157 comments

What's fascinating to me about this phenomenon is that you can actually feel the 60Hz AC by running your hand across the lid.

It feels as if the surface is slightly bumpy, but the width of the bumps changes as you adjust the speed your finger moves.

Unplug from mains, and the surface becomes smooth.

As the answer notes, this only happens when using the two-prong adapter without earthing. It also seems to be more noticeable when connected to older buildings.

I felt this on an Apple laptop in California a couple of years ago, in an apartment with only two-prong outlets in it. I'd describe the feeling more like the laptop cover was vibrating, rather than bumpy. The feeling went away and the laptop cover became smooth and normal if I lifted my feet off of the ground.

Once all the outlets were rewired to be three-prong, with ground, I used a three-prong power cord and the problem went away.

Pretty scary feeling, and scary to think that two-prong outlets and appliances are legal anywhere. I'd also be surprised if Apple hasn't been sued at some point by someone getting electrocuted when using their laptop and a non-grounded, two-prong power cord.

> and scary to think that two-prong outlets and appliances are legal anywhere

In Japan, two prong outlets make up the vast majority of sockets, it kinda sucks.

I don't think I've ever seen a three-prong outlet in Japan (maybe only new installations?), but "earth screws" are quite common (any room prepared for an air conditioner will have one at least) http://www.hakusui-trading.co.jp/safety/img/img02.jpg

What? That's crazy looking! Why not just put the third prong in there if it's wired up to handle a screw?

What's the point?

Just guessing here but I think it's to allow easy grounding of old appliances and other equipment that might risk contact with electricity but are not grounded by default. Metal frame desk as example.

Very clever actually.

And the cable on the left here is what the included Apple MacBook power cable looks like, with the little earth wire sticking out to screw on http://rinare.com/wp-content/uploads/image_archive/110801_2....

I think it's just a legacy thing - historically, the only things that needed grounding were static appliances like fridges, washing machines and air conditioners. The manual in our fridge has this instruction for earthing http://mayoyo.tokyo/jIe.jpg

I need to revise my comment that "I don't think I've ever seen a three-prong outlet in Japan", because now that I have power sockets on my mind, I just saw a three-prong outlet at my gym. So I guess newer buildings have them.

They're starting to become more common in newer apartments. For some reason my apartment has one outlet panel with two of the three-prong outlets, but the rest are two-prong. Except for the air conditioner and laundry machine sockets, which have the earth screw like you described.

120v isn't going to hurt you, just scare you. You have too much resistance.

You can die with 50V. It's not the voltage that is important but the amps.

You can also die if you stick your finger for a long time (24H) in a small current.


This doesn't only happen with the two-prong adapters, I have noticed this on a few MacBooks, plugged in using the standard 3-prong UK plugs (sometimes with my phone too). An even weirder feeling is when someone else is touching the laptop, if you run your finger over their arm you'll notice the same bumpy feeling.

Oh my god, this is the feeling my ex and I could never figure out. One of us would touch the other, and there was a weird vibrating sensation as one would move their hand along the other's skin. I can't believe I never thought that it might be the laptop.

This effect can be used for tactile feedback on touchscreens:

TeslaTouch: Electrovibration for Touch Surfaces:


Video: https://www.youtube.com/watch?v=FiCqlYKRlAA

So that's what it is! I assumed the source of that effect is some micro vibrations from fans, or because of some weird electromagnetic effects from parts placement. It happens both a on an HP ZBook and an older Macbook Air. Thanks for solving this mystery - moving to a better connector helped.

Well that explains what the weird feeling I used to feel when touching a 2015 Macbook I was using last year. It felt exactly like that (as though the surface was bumpy) though I never got far enough into debugging it to figure out that it was actual charge leakage onto the case and that I was feeling the AC current. That's a bit scary.

Question: aren't laptops powered off DC (there's a rectifier/transformer combo in the power brick) so how would AC get to the case of the laptop?

Laptops are indeed powered off of DC, which means that there will be a constant voltage measured across the positive and negative pins of the MagSafe plug.

However, the voltage measured from either pin to ground might very well fluctuate. Without the grounding pin on the power supply, the DC side of the supply may 'float' with respect to earth ground. If you plot the voltages measured from each pin to ground, it probably looks like a pair of sine waves, one shifted 20 volts above the other.

Right, so there's no relative phase change between negative and positive terminals but there is a phase change between the terminals and ground (which can be interpreted as a frequency relative to ground)? And since I'm grounded I experience that frequency? Interesting. Is there a relation between the "float frequency" and the AC freqency? Is it the same because of how commutators work?

I suspect that the float frequency is generally equal to the AC frequency, but I suppose it may be possible for it to be some subharmonic of the switching frequency, assuming you've got a switching power supply.

The socket isn't grounded the laptop on your desk and you are, so you get socked, I had the same thing with my tower case when I moved a flat I discovered that the socket I was using had the ground and hot terminals switched.

This is a common problem, the power cable from the power adapter to your laptop is also usually connected to ground, if the ground is hot then you get shocked.

Easy way to cause it -- connect something that's got it's own cheapo AC power supply (eg. phone charger, speakers) to your computer via USB. The DC grounds are linked via USB, but the different power supplies end up with a wildly different DC ground wrt AC ground from each other, which can cause buzzing noises or the surface feel you're talking about.

Bring back transformers! (ok, don't, but...)

I had this in my iPod touch. It feels "bumpy" when plugged into the wall. I thought I was going crazy.

I've experienced this with appliances other than computers, such as an old fluorescent desk lamp with a two prong cord, and I wonder if it was common before the adoption of double insulation. I looked at the computers in my house, and realized that they all have plastic enclosures.

My old 2011 MBP and MBA do this when plugged into European 240V power

This has been happening to me in both UK and Ireland, which use three pin plugs as standard, with every metal-bodied Mac I've owned since the Titanium PowerBook came out in 2001

I discovered you can also switch the on and off by connecting and disconnecting your feet from ground.

Feet on the floor => shocks.

Feet on the beam of a wooden stool => no shocks.

I'm deeply curious about this! Is it possible to recreate the situation at home, or does this require something miswired with the mains power supply or power adapter, or an older MacBook Pro?

connect the two prong adapter, take your shoes and socks off, feet on the ground... feel the vibe! the best shocks you get at the edges or at the pointy edges in that groove to lift the display up.

> feel the vibe! the best shocks [...]

Users enjoying electric shocks. Reality distortion field operating at nominal.

right, it's so powerful it's also interfering with your sarchasm detector, apparently.

My macbook was stolen years ago, but I remember it doing this exact thing. I never really looked it up or thought about it until now. It is a totally weird feeling for sure.

I am sure that's a feature by Apple, they want to give you a nice 9V tDCS running through your brain to make you more productive ;-)

Or it is a side-effect of Apple's reality distortion field :)

I have this problem in India. I suspected the mains was dodgy, because during the many power outages i never got the shocks when on UPS.

I got a multimeter and measured. The neutral was 70V and the phase 300ish. So the difference was roughly 230V but a switched power adapter would make this hover around 70 too (I believe an old coil based would probably been fine).

The Indian electrician didn't understand my problem because his only tool was a regular bulb with two exposed wires that he jammed into the socket.

"Look sir, light, power working"


Shark used to make an (otherwise excellent) upright consumer vacuum cleaner with a metal strip in the handle. The vacuum's power cable did not have a ground.

This vacuum had the most five-star reviews on Amazon, but then a minority of people started complaining and leaving one-star reviews, saying they were getting shocked.

The reactions from the fanboy crowd were non-sympathetic ("you're imagining it," "it's just static," etc.), and they mass downvoted every one-star review. Some of the people claimed they were getting shocked PRETTY HARD, too, as in it knocked them over. IIRC, even Shark responded saying that it was impossible for the vacuum to shock you.

I remember seeing this while looking at vacuums for my elderly mother who has a heart condition. To the electrical engineer in me, everything made sense!

I started defending every single one-star reviewer person, and I wrote my own very detailed review with photos of the handle. Soon, the tide turned, and more people started upvoting my review than downvoting it; and I even received personal "thank you" messages from the people who got shocked ("finally someone believes me").

It eventually got to the point where a year later in 2014, Shark released an updated model with no more metal strip. Seeing this, I bought the new model for my mother. I'd like to think I can give myself SOME credit for causing them to do that.

Not only that, the upvotes from that alone were a good part of the reason I became an Amazon Top Reviewer.

Why would you still buy from the same manufacturer that denied bad (and potentially deadly) design?

Like I said, it was otherwise, an excellent vacuum. Any how, I know about Lenovo's Superfish and recently its attempts to block Linux installs, but I am still a die-hard Thinkpad user because these are very large organizations where all it takes is one single person's oversight to cause a mistake.

They didn't "attempt to block Linux", they just shipped hardware without a Linux driver.

And later released a workaround to make the hardware work in a slower, more power consuming backwards compatibility mode so Intel can continue not properly supporting the hardware in Linux.

But sure, it was totally "Lenovo blocking Linux".

I'm afraid you're misguided here.

Lenovo initially released a BIOS with a goto statement added to jmp out of the disk controller mode setting (which is normally present and allows the user to change back to AHCI mode). Reverse engineers on the Lenovo forums discovered this modification while studying the disassembly.

Then, one user patched the BIOS and manually reflashed it using an SPI flasher and some soldering, and Linux worked just fine by detecting the drive.

Yes, the ideal solution is that Intel gives specs to OSS devs to build a driver (or even builds on themselves), but the path of least resistance is to have Lenovo unblock that BIOS setting, which amounts to changing one line of code, or 15 minutes of one engineer's time.

> Lenovo initially released a BIOS with a goto statement added to jmp out of the disk controller mode setting

Because switching to AHCI mode with Windows installed would brick the machine (Yay, Microsoft), and Lenovo foolishly assumed that people who wanted to use Linux would buy one of the Linux certified machines instead (X1 Yoga and 60 series Yoga devices are all certified: https://support.lenovo.com/us/en/documents/pd031426 – but I'm sure that's just more proof that Lenovo hates Linux for some reason).

> the path of least resistance is to have Lenovo unblock that BIOS setting, which amounts to changing one line of code, or 15 minutes of one engineer's time.

Which is exactly what Lenovo did: https://forums.lenovo.com/t5/Lenovo-Yoga-Series-Notebooks/Yo...

"Because switching to AHCI mode with Windows installed would brick the machine"

There are tons of BIOS settings that could "brick" my machine though, it's a weak argument, really. My car didn't come with a lock on the hood.

"Which is exactly what Lenovo did"

Okay, you're acting like it didn't require any teeth pulling on our end to get them to release it (check out the 30+ page forum topics).

How come Intel is one of the top contributors to linux, but doesn't ship drivers for all their hardware?

Different divisions doing different things. Intel is extremely interested in Linux for their HPC Itanium/Xeon range, moderately interested in Linux for other server and business hardware, as well as mobile; and Intel's consumer PC division doesn't give a fuck at all.

I'm guessing because Linux on laptops isn't a big money maker. Linux on server is where Intel focuses.

I would separate the issues, vacuum cleaners are famous for electrically charging dust up to quite high voltages.

I should clarify that the reports indicated that the shock originated from the hand touching the handle.

I guess I should go further: some vacuum cleaners have to have a ground connection in the hose, to try to discharge the dust. If they removed it for unrelated reasons, they probably lowered the overall quality of the product overall.

To Shark's defense, I haven't seen too many non-commercial/consumer vacuums with grounded plugs.

That said, they (consumer vacuums) almost all have enclosures made entirely of plastic.

I had the same problem in Australia. I thought it was just me being over-sensitive to static electricity

It took me 6 months to get PowerCor to understand the shower was trying to use me as an earth, because they couldn't reproduce it. They told me I was just being sensitive, despite every flat reporting similar issues.

The hot water pipes were being used as the earth, and the electricity could leap across the pipe in bad weather.

You are probably connected to poorly grounded socket or a socket where hot and ground were switched.

I had a grounding issue and I used to get shocked by my tower all the time, this is pretty common.

Same here, with some PCs back in a shop area. Come to find out, the outlets weren't getting a good ground due to painted conduit. And without a good ground, a cheap surge suppressor ended up dumping about 30 volts into the ground pin.

Neutral can be as high as 400v relative to earth and the power still be within specification. 30 volts is more typical though.

It's the devices responsibility to design for that.

The 70v is probably induced voltage at milliamp levels.

You can fix it by bonding the neutral to ground at the breaker box.

This is potentially deadly advice. A neutral/grounding fault will energize all your home devices with live potential; same with a live/neutral swap (unlikely but possible with Indian wiring standards).

> This is potentially deadly advice. A neutral/grounding fault will energize all your home devices with live potential; same with a live/neutral swap (unlikely but possible with Indian wiring standards).

You are wrong. In the US the NEC requires this. If you bother to look inside your breaker panel you will find the neutral and ground wires are literally screwed down to the same bus bar.

Any path your body (or the soil outside) can provide back to the generator pales in comparison to the neutral tap provided by the transformer. Grounding to dirt is about static electrical discharge, not the voltage provided by the generating station.

The safety of providing a grounding wire is that metal parts of appliances must be connected to that ground. The ground wire itself is both bonded to neutral and connected to a metal grounding rod driven into the dirt. If any part of the appliance's internal works becomes energized and touches the metal casing the direct path to ground is designed to create a short circuit and trip the breaker immediately, rather than sitting there waiting for a human to come along and complete the circuit.

If ground weren't bonded and the ground dried out or the grounding rod weren't properly installed then the scenario you describe would occur. A single faulty appliance would back-feed voltage onto every grounded appliance in the building. So in fact bonding is what creates safety, not the other way around.

> In the US the NEC requires this. If you bother to look inside your breaker panel you will find the neutral and ground wires are literally screwed down to the same bus bar.

It could be different in US, but in modern European installations the PE and N bars are separate; older installations use common PEN; and even older ones don't even have PE. Each of the wiring schemes requires different approach and poses different hazards. There's no single recipe that would work on all of them.

My bottom line is: don't make arbitrary connections in the breaker box without proper knowledge and training; and don't give random electrical advice on the internet without knowledge of local codes.

> It could be different in US, but in modern European installations the PE and N bars are separate

In the US a single PE+N wire feeds into the building. All building wiring is separated as in Europe. They are tied together in only one location, usually wherever the main switch is.

Just like Europe, really old installs in the US don't have ground (PE). Some are retrofitted with ground like my house in SF. One thing people should never do is connect neutral to ground at a secondary point. It can be tempting when you don't have access to run a ground wire but creates a serious potential for safety problems. The way to handle that is to install a GFCI (RCD) plug and put a sticker on it stating "No equipment ground" - the outlets actually come with those stickers for that purpose :)

As far as I know in European systems where the building has separate PE+N feeds they are still bonded together, it just happens at the transformer. I could be wrong about that though!

In separate PE+N systems, the feeds join at a single master GFCI (typically one per distribution panel)

I downvoted you because again this is potentially dangerous advice for the plurality of people who live outside the USA, without referring to local standards.

For example in the UK neutral is traditionally grounded at the electrical substation, which serves several hundred homes, and all lines are separate / unbonded within the house.

In the most recent PME standard in the UK the earth and neutral are bonded back to the substation as the Protected Earthed Neutral but that is achieved on the supply-side, not the in consumer equipment.

> You are wrong. In the US the NEC requires this.

OP's very first sentence clearly stated they are in India, where this is obviously dangerous advice because most devices (and piping) connect their surfaces to Earth, which is new Neutral.

Yes. In my previous place in India the RCD was repeatedly tripping up.

Earth here was a metal rod into the ground, and I only found out much later they fixed the RCD issue by disconnecting the rod and I started getting electric shocks from touching my fridge while my crappy toaster was connected.

That's when I decided to not mess with electrics in India. It's dangerous enough as it is.

As for the 70V, I eventually managed to reach someone in the electrics company that understood my issue, and they told me a local transformer for the whole street was broken. And they didn't have any plan to fix it.

My 120 volt inverter installation manual required me to wire one of the 120v outputs to a solid ground.

My understanding is that it's caused by Y capacitors in the power supply's EMI filter leaking minimal amounts of current onto the case. As others have mentioned, proper grounding usually fixes the issue - although in one case I had to rewire an entire apartment because someone had a very lopsided idea what the PE wire is for. It was for a friend with a metal Macbook Pro, an exceptionally sensitive skin, and way too much time & money on their hands. :D

The usual word of caution: I'm trained in electrical installations. A layperson - even one skilled with a multimeter and a soldering iron - should never attempt to modify ground connections or power distribution. There are dozens of potential (and very deadly) failure modes that require proper training to recognize and prevent.

I have a mid 2015 13" MacBook Pro and I've measured up to 48v off the chassis between ground on properly wired circuits. I began investigating this after getting mild shocks after working out (sweaty) and while working on the MacBook in my lap while working on a PC laptop on my desk which also has an aluminum chassis. I tried an isolation transformer and the issue disappeared. I contacted Apple about it but crickets. I then did some current measurements and it was very low and of no concern at that voltage so I decided not to push the issue. As other have said, the solution is to use the three pronged cord that came with the power brick.

You can feel this effect for yourself by using the two pronged plug and finding something grounded to the chassis to touch. With one hand, hold the grounded item while moving the palm of your other hand around the backside of the led. It's a bit dependent on the conductivity of your hands but I've found most people can feel it, even my dad who's a farmer and has very dry hands. Remember, if you get electrocuted, it's not my fault, it's Apple's. They have much deeper pockets than me.

Ungrounded adapter + bad mains power = zap!

Ungrounded adapter + clean mains power = probably no zap

Grounded adapter + bad mains power = probably no zap

Grounded adapter + clean mains power = no zap

It's not just the adapter and it's not just the mains power; it's when both come together. Electricity follows pretty simple rules when it comes down to it.

Always always always ground your A/C connections. Why wouldn't you?

Also, never use one of these unless you've attached the little wire/alligator terminal to a ground somewhere:


I knew a guy in college who rented a house that didn't have any outlets with a ground plug.

This became such a problem, he made his own ground by using a big metal pipe outside the house that was already deep in the earth, and running a wire from it to where he kept all his equipment.

Then he used stuff like in that picture to make sure he could ground all his equipment.

This is the right way to use those! It's so rare to hear of proper usage.

You can also screw them to the outlet box, which should already be grounded, especially if it uses older BX sheathing.

Actually, for things with a non-conductive casing (think cheap nightlights, or those apple wall warts) there's no need for a ground. If anything, it's another part and more cost, thus it isn't included.

In highly sensitive A/V systems, an isolation transformer is often used as well, neglecting a ground.

You have to be careful with isolation transformers because there is one gotcha... the ground pin normally passes through to earth. I've witnessed someone blow up a nice $5000 Agilent oscilloscope before I could stop them because they didn't understand how to use an IT and plugged the scope into it so they could probe AC. Bad news, you're supposed to plug your test device into the IT not the scope because the BNC connectors in almost all oscilloscopes are connected straight through to the earth pin.

I heard "POW" from across the lab as soon as he clipped the probe on and knew I should have warned him. Nobody was hurt apart from our lab budget.

Humorous demonstration of the same mistake: https://youtu.be/sI5Ftm1-jik?t=2m20s

I can't tell, the second boom where he holds the resistor in place was that on purpose? If so holy shit that's a dangerous way to make the point. If it was also an accident then he is lucky to be alive since he doesn't seem to know what he is doing.

I know this video is supposed to be funny, but I couldn't bring myself to laugh. Too many people die making the same mistakes.

He does know what he's doing and it certainly was deliberate. While most of his stunts probably hurt he doesn't set them up exactly as he presents them (I.e. it's usually not mains).

These are all better and more knowledgeable points than my own! I definitely only speak out of an abundance of caution having known people whose bad electricity and habits have damaged property.

I got the zaps. I live in the Uk where we have good quality mains power, and my mains power and all the sockets are tested once a year.

"clean" mains power has nothing to do with zapping. Where'd you hear this? I've literally never heard this nonsense before.

I suppose a neutral line with a nonzero voltage could be called "dirty", but not in the traditional noise sense.

That still doesn't cause zaps unless you were living in the Edison days or something.

That's exactly what caused minor zaps on older equipment that has a metal case connected to the neutral line.

How old are we talking about? That sort of shit hasn't been happening for ages.

I definitely used the wrong word -- I intended this meaning.

Geez peoples - so much misinformation. Touch current test methods and limits are well-defined through out the world. Poor power 'quality' may affect this measurement, but is not a significant contributor to the magnitude of potential leakage through the ground wire or through exposed metal surfaces. It is a function of the power conversion equipment connected to, or internal, to the device. Even where wiring does not meet code, the upper limit to this measurement is well defined per the simulated fault conditions required in the test methods.

People that claim to be engineers need to read and understand the basic physics behind the product safety standards scoped by your equipment. For EU, code is defined in BS7671/IEC60364; and NFPA70 (mostly article 250) in the U.S.; and similar stuff in C22.1 for Canada.

ITE power supplies must meet the locally harmonized version of IEC60950-1 (soon to be obsoleted by IEC62368-1). Where there is no ground pin, North American power supplies must meet UL1310/CSA No.223. These standards all have specific limits for voltage, current, and VA levels that can be exposed to the end-user, for both normal and abnormal operating conditions.

> Where there is no ground pin, North American power supplies must meet UL1310/CSA No.223

So, as far as I can tell, with a brief skim of the standard, a class 2 device should have no more than 0.5 mA leakage current, right?

I just measured the leakage from my macbookpro through my body to ground and it's about 50 μA. Well within the limits.

So I guess that's why they never did anything about it. Still amazing that you can clearly feel this current: if you lightly brush your wrist around the sharp edges it actually hurts. I wonder how 500 μA would feel.

Depends on the 'bandwidth' of the signal and the test equipment and the individual. Generally consider many non-medical measurements below 025mA suspect, as few design engineers make an effort to understand the various frequency components of the voltage and current leakage signals, and/or understand the effects to the signal of instrument impedances.

Have had several discussions with Mr.Pete Perkins (he sits on several STCs and has written several IEEE papers) on this subject, and we agree that the human body model referenced by these safety standards being used for the measurement network (IEC60990) have problems because the medical community does not understand physics. As the various standards committees continue to look at the body of work being done by bioengineers, will probably see better measurement methods being codified.

Human response and perception to electricity has significant variance and resultant effects/affects. My wife can detect less than 10uA at 200Hz/42V. My detection threshold is at least an order of magnitude greater, even at 50Hz.

Need to correct some stuff.

Class 2 (arabic numeral) is for limited power sources, regardless of construction class.

Class II (roman numeral) indicates a construction class where safety cannot be dependent on a ground bond.

Class I (roman numeral) indicates safety is dependent on a reliable ground bound.

Class I equipment, depending on the scoped end-use equipment safety standard, can have up to 25mA of leakage.

Class II equipment, depending on the end-use environment, can be limited to 0.25mA of available touch leakage.

A good reference for Class 2 and 3 equipment is the UL5085-x series (same as CSA No66.x).

For the EU, there are no harmonized standards in the Low Voltage Directive that have an equivalent Class 2/3 construction, although there are several safety standards that address requirements for 'inherently limited' power sources.

Due to EMI reasons, for switching converters, the hot and neutral terminals of mains input is generally capacitively connected to the Earth prong via high frequency capacitors. That means if the earth prong isn't properly connected to actual earth, the earth prong now has your mains voltage divided by two on it. If the earth connection happens to be connected to the chassis, there's your shock.

It probably won't kill you unless you have a weak heart or if you're really unlucky because the EMI suppression caps are small enough to not supply lethal current, but can be really annoying.

I've had this on every metal-chassis Mac I've ever owned. The chassis typically floats around 50V AC at 50Hz (in the UK, at least) - making it noticeably vibrate and tingle when you touch it, especially with the palm of your hands when typing. It also seems to make RSI worse.

The solution, as everyone's pointed out, is to ensure you are correctly grounded.

Doesn't anybody have a DVM around? If you can feel a stray voltage, measure it, and find the source.

As someone else pointed out, get an outlet tester.[1] They're about $7. You may have an open ground, or reversed hot/neutral. Once you've eliminated that, suspect the power supply.

Make sure you have a UL-listed power supply. If you're getting stray AC voltage on the output side of a UL-listed supply, report it to UL. Here's the form.[2] There's no excuse for that.

[1] https://www.amazon.com/Amprobe-ST-101B-Socket-Tester/dp/B008... [2] http://www.ul.com/customer-resources/market-surveillance-dep...

About reversed hot/neutral. We have these[1] symmetrical adapters in Europe. How are you supposed to know the proper orientation? You are not. Because you either have an earthed metal case or you have a double insulated device.

My magsafe adapters have a "double insulation" symbol, a tiny tiny one near "UL Japan", but still need a earthed prong to not feel any shock from the laptop metal case.

1. http://images.apple.com/support/assets/images/products/ac-wa...

Test the outlet for proper wiring. If you're in the US, buy one of these: (there are similar models for use in other countries)


If this says good (two amber lights) and you're still getting shocked, follow up with a voltmeter and/or qualified electrician.

Don't use Macs but I'm surprised Apple apparently didn't give an earthed power adapter by default on a metal skin product. This seems like negligence.

Now that I think about it, my iPad's the same when charging.

In the U.K. they come with earthed plug.

However I still noticed "buzzing" in the MBP, MBA and even iPad when I would touched them.

Took the MBP in to the store. It didn't buzz there. They gave me a new power supply anyways and recommended I connect the plug directly into the wall socket.

Turned out that the power strip I was using is not grounded even though it has three pin sockets !

When I plug Apple devices directly into the wall socket I don't notice any "buzzing".

So now I don't connect the Apple devices via a power strip.

My UK MacBook came with two plugs; one with a long cable and an earth connection, and one "short" one that's just the plug head, with no earth connection (the slot that the earth ring from the transformer connects to is just plastic inside).

I get the shocks when using the short connector, and always have.

Here is a DIY guide by someone who figured out how to fix the issue (danger, electricity, don't kill yourself)


Throw away that power strip.

As in, right now. It violates every electric safety law around.

I would rather at least try to disassemble it before throwing away - otherwise it is likely that someone will pull it from the bin and use it or sell it.

They do give one by default, but you can disconnect it if you so choose.

FWIW, I have never had a problem using the two pronged plug in the US. It's interesting to see all this preexisting problems with MacBooks surfacing after the recent release of the MBP

They stopped as of the new MacBooks this month :/

Wow. More expensive and includes less... I don't know what they are thinking... I never even though of Mac's shocking people under normal use. wow.

They don't include them anymore in the 2016 MacBooks

There's also a good chance that, at least in part due to Apple's greed and extravagant prices for chargers / fragile power cords, many people are using knockoff chargers and don't know it. See also Amazon happily selling knockoffs as real -- Apple claims 90% of chargers it recently bought on Amazon are fake and is suing the supplier, though unfortunately is not suing Amazon [1], which might help Amazon find the will to stop people selling fakes.

[1] https://9to5mac.com/2016/10/19/amazon-fake-apple-chargers-ca...

Have you seen a tear down of the authentic chargers? There's a lot going on in there.

Right, but even still, you don't think Apple's commanding actual profit from them? They're up to $90...

This was a really good teardown.


The author also does consider the cost of the components.

As mentioned below, a reasonable estimate of the cost is $30.

They could also sell replacement user swappable magsafe cords and defang many of the complaints. But then they couldn't effectively charge $90 for a replacement cord.

I have wanted that cord to be replaceable forever. At least it finally is now. Given how many the kids and dog destroy I consider it an improvement.

I have wondered if the degradation of the cord wasn't some sort of safety guarantee rather than planned obsolescence. When the cord wears out you buy a new one instead of using the ancient one from eight years ago.

I never had that issue in the US (even when using a two-holed outlet), but I had that problem when I was visiting Israel. So it seems to only be an issue when using 220 volts and not a proper ground connection.

I get it in my apartment (I live in the U.S.) which is brand new with 3 prong sockets if I have my feet on the ground (concrete floor) while roughing the laptop.

I've experienced it a few more times at different peoples houses as well.

You might buy an outlet tester and see if your hot/neutral are reversed or if ground isn't connected. If it all checks out you can use a multimeter* to check potential between neutral and ground. If your apartment is wired correctly there should be almost no voltage between the two.

At the breaker box the neutral and ground are supposed to be bonded together. That means only minor induced charges inside the building wiring would show up between the two. If there is any significant voltage then something is leaking on one of the lines or ground might not be bonded... it could even be floating if they didn't bother driving the grounding stake deep enough and the soil dried out a bit.

> At the breaker box the neutral and ground are supposed to be bonded together.

Note this advice is country-specific. In some countries, the bonding is done further away from the house.

In any case, you should never trust the neutral line to be an earth. If a fault occurs that disconnects the neutral line from the supply, your neutral line will have deadly voltage on it by virtue of being connected to live through your appliances. Moreover, depending on the multimeter you use, if you measure the voltage between neutral and earth, you could possibly trip the RCD in the distribution unit (if you have one).

The rules are simple in most countries - if it has any touchable metal parts, it must be earthed.

I noticed the vibrations while charging in France and Germany with my American iPhone and MBP, but just chalked it up to my universal power adapters being not 100% native.

Reading jordwest's 60Hz comment, it seems to do with grounding. So do MBPs and iPhones purchased in Europe still experience this issue if the apartment isn't grounded properly?

I have this problem every winter. With my Macbbok it was the worst, it even caused the trackpad to stop functioning once, but it has also happened to some of my other devices as well.

It's happened so often to me that I've trained myself to touch something to discharge the static before touching my equipment.

Same here. I've only had the issue in Thailand. No shocks at all in the US.

I sometimes run into an interesting variation of this kind of problem. I often work with a Microsoft Surface tablet laying in front of my MacBook Pro, with my arms stretched over the tablet to type at times.

If the Surface is plugged in (no ground pin) and the MacBook Pro is also plugged in (ground pin), and my arms touch both at the same time, I can feel a tingling that quickly becomes unpleasant. Unplugging one or the other seems to be a work around.

That solves an issue I've had as well, though it shows the MacBook Pro isn't really the fault. I have a Samsung TV (no ground-pin) and I would often watch it while using my MacBook Pro plugged in (ground pin). Because I didn't have wireless headphones yet I'd run a cable from the Samsung's headphone socket and plug my Bose headphones into that. If I was touching the MacBook case with one hand and grazed the metal parts of the 3.5" audio cable, I'd get quite a strong tingling & that almost becomes painful. Hadn't considered that the fault was the TV's lack of grounding.

FYI, I can't remember which way round it is, but only some of the UK 3-pronged adapters are actually earthed (as I discovered after having this problem myself).

I think it's the extension cord that is properly earthed, whereas just the plug attachment that goes directly into the power brick is not. You can tell by looking up into the adapter (the part that plugs into the power brick) and seeing if it's metal or plastic...

A certain vintage of Apple adapters have plastic posts where the ground would otherwise attach. This image is iPad 10W adapters, but the same follows for some older iBook/MacBook chargers:


Double insulated appliances are fine, the circuit just needs to be designed with double insulation in mind.

Yes, i had that problem. I used this workaround to fix it:


I've run across this before - once I measured the shell of my MBP at 90 volts DC.

If you don't have access to a 3-pin charger, you could always use a separate earthing setup, such as an antistatic mat: https://en.wikipedia.org/wiki/Antistatic_device#Antistatic_m...

90 volts above earth ground? Or relative to something else?

It was a long time ago, but iirc it was relative to the nearest available metal object, which I think was the metal frame of a desk. It wasn't a super rigorous test. :P

I had the same happen to me while using a cheap ebay charger. Never happened with a genuine one.

There's an interesting post about the internals: http://www.righto.com/2015/11/macbook-charger-teardown-surpr...

Some time ago, Apple launched a recall program for defective power adapters:


I had the problem mentioned in the subject. Replacing the plug adapter has fixed it.

For those of you who don't have access to proper grounding (because, for example, the wiring lacks PE or it's faulty): a plain separation transformer (1:1) between mains and your laptop might be able do the trick. Unfortunately if you have a larger setup (speakers, monitor, etc.) you have to connect everything to the separation transformer, otherwise you'll create leakage a path to mains some other way (say, through the audio jack).

Caveat emptor: If you decide to go that route, make sure you can return the transformer if it doesn't to the job.

Yeah no, that won't work.

Why not? Hospitals used to use isolating transformers for surgical electrical supply precisely to prevent any possibility of electrocuting patients.

My first summer job was doing IT for a small outfit, who worked out of an old house converted into an office. They had eight machines, all connected to a LaserJet printer via a parallel port switch. The parallel cables ran down into a crawlspace under the house, and it wasn't uncommon for one of the cables to work its way loose. No problem, tighten the parallel port connection at both ends, and you're back in business. But, being an old house, many outlets were missing ground pins. I must of electrocuted myself twenty times that summer.

I've had this on two MacBook Pros here in Australia. On the first one I took it in to a Genius Bar appointment and, while they acknowledged it happens to a "rare number of people", they basically said tough luck and to use the earthed power cable which is about 1.5m longer. By the second time I just accepted it as part of owning a MBP.

As an aside, I should buy a lottery ticket given the number of rare issues that happen to my Apple products.

The point is, how did Apple manage to get away with it for all these years? why weren't they enforced to ship only the properly grounded adapter?

With a trotted meme/slogan like "You're holding it wrong" sorta explains it all does it not?

I say this as a happy MacBook Air owner but i'm traveling soon and this had better not be an issue...

Because the fanboys will suck up everything but a touch screen on their laptop.

I've noticed a similar problem. I have a macbook pro and a macbook air and whenever I have both of them plugged in and am touching both of them at the same time (usually one arm laying across both of them)

I can feel where my arm is touching the laptops start to hurt/burn. I figured the electricity is now going through my body, but assumed it was a problem with the laptop, not necessarily the electricity.

My iMac, specifically the USB keyboard (I needed the numpad), gives a slight electrical sensation when I touch it anywhere other than a key.

I experienced the same with an aluminium Apple keyboard connected to a non-Apple PC; small electric shocks now and then when I touched the aluminium. I contacted Apple about it and they said it was impossible .. Luckily I had purchased the keyboard online and I could still return it.

I'm curious if this would trip a GFCI when you touched the lid.

People often judge whether they will get shocked based on resistance, but humans are also capacitors. The casing of a macbook is a machined aluminum frame which will act as one plate in a capacitor. Your hand is the other plate. Unlike DC, AC passes through capacitors.

Also worth noting: some of the cheap knockoff magsafe adaptors available on ebay have an earthing "pin" inside the adaptor (the mushroom thing) which is actually just coated in a metallic coloured covering/paint.

This doesn't actually provide contact to the existing ground pin, so you have this issue.

My toughbook does this as well. One of the replies there says thinkpads have the same problem, and I have an IBM power adapter, so that could be the culprit. IIRC it's high frequency, so probably created by the supply itself rather than a floating neutral in the building wiring.

Maybe a stupid question, but why is the case grounded at all (I mean as in "put on a common zero potential", not as in "connected to earth")? I imagine it is convenient to use the case as common ground, but it seems wierd. Is is unavoidable production-wise?

This happens to me regularly when I go back home (to a foreign country not the US). All the sockets have ground but the ground doesn't actually go anywhere... So you still get shocked. My solution was a bit lazier: plugin my MBP only when I'm not using it...

I had the same problem with the small plug. Using the extension cord with the ground solved it.

I still remember some Dell Precision workstation having a "magic touchpad" as it reacted even when your fingers were an inch away - must have been a pretty powerful electromagnetic field! And the case was always giving shocks at random times.

Well, that explains it. Just last week my son was complaining that he was getting tiny shocks from the chassis of his Macbook. I thought he was just making excuses to not do his homework and told him to stop imagining it.

Time to buy a 3 pin adapter!

Happened to me too with my 2011 macbook air and my 2010 macbok pro 15' when using the 2 prong adapter at home in Europe. Currently typing this on a 13'' late 2014 13'' MBP with 2 prongs in Japan. No problems.

If you can get a shock from this, and as someone else is saying that they can feel it when they wave their hand over the lid, then how is this passing any EMI screening?

That's got to be noisier then an old ham radio.

I would suspect it's a common problem with aluminum casings in general. They also have that cold feeling. IT's one of the reasons i prefer the matte plastic of thinkpads.

I have the same issues when I'm in Bulgaria during the summer (220V, 50Hz), and always wondered how Apple did something so basic so terribly wrong!

Well this is just great. I'm traveling overseas to a country with 220v (South Korea) and I am concerned my Air will end up shocking me.

I thought I was the only person to get shocks of my Macbook Pro, and that it had some problem. All because of the lack of a third pin.

I'm assuming this is the same phenomenon with a metal-body camera I have - even though it was only charging off 5VDC at ~1A.

This problem is common.

You can solve it by opening up the power supply and ripping out the bright blue Y capacitor inside. It looks like a slim M&M with 2 legs. Both apple official and 3rd party power supplies will have one.

Do not damage the capacitor without removing it - that could lead to an electric shock. You can remove it by cutting it off with pliers or wire cutters.

The power supply will work fine afterwards, but might emit a bit of radio interference, although generally not too much.

> might emit a bit of radio interference, although generally not too much

It might not cause the FCC to knock down your door, but what will it do to the laptop's own wireless and Bluetooth connectivity?

Care to explain what this does?

Could somebody draw a simple diagram with resistors and perhaps capacitors to illustrate what the problem is?

So i am guessing the UK plug wont have this problem?

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