They can’t, it’s caused by the capacitors required to suppress electromagnetic interference caused by the switch-mode power supply. These allow a very very tiny amount of current to leak through from the mains side, which is then capacitively coupled to the metal case (IIRC Apple do not connect the case to power negative) reducing it further, but it’s enough for humans to sense it.
replyIt can be avoided by using a grounded power supply, but because there are large countries that have ungrounded outlets in common use the most designs are ungrounded.
Why do only Macbooks suffer from this problem? When I had a work-issued Macbook I charged it and my personal Framework off the same USB-C charger and I only every felt the leaking current from the Macbook
replyIt's not only mac's suffering from this problem. My old dell latitude with magnesium case had the same thing. I didn't fully understand why and some people thought I was mad for feeling it but it was there.
replyOnly Apple is insane enough to make actual laptop chassis with unpainted anodized aluminum. Others either do it in plastics and/or painted metal. And paints are kind of liquid plastics.
replyAdditional question: why do only some people notice?
replyIt’ll depend on how well grounded you are compared to how well grounded the laptop is, where it’s touching your body, and your sensitivity to electricity which varies.
replyMy aluminium body Lenovo IdeaPad has exactly the same problem.
replyThank you for explaining this! I've been feeling this on my girlfriend's macbook for years and I've always wondered what the hell that was. :D
replyDefinitely been a long standing issue on many laptops with exposed metal parts. Late 90’s, if I used my brother’s Compaq while putting my feet up on the radiator, the metal speaker grills would give me mild shocks.
replyI once had an HP with an aluminum case and it had a grounded power supply but if you plugged it in without grounding his an adapter (sometimes you gotta do what you gotta do). You could feel it straight up vibrate while conducting current if you rubbed your hand over it. Not enough to shock me but it felt like kind of a shoddy design and leaked a lot more current than I've felt on a MacBook.
replyIs that what it is! On my pre-unibody MBP I used to run my finger across the body sometimes and it had this weird wavy feeling (honestly can't describe it well). I thought it was just a quirk of the aluminium itself!
replyYou can fix it by switching to one of the grounded charger heads. Unfortunately in most locales those are only available with an integrated extension cable (or as everyone seems to call them, the "gooseneck" cables)
replyIt happens with other 2-pin chargers on both MacBooks and other laptops, but it depends upon various factors how strong the leakage is
It's also an issue on the new Neo. It was the first thing I noticed when I tried one in the Apple Store. I unplugged the power cable and it went away, replugged and it came back. I'm in the UK so I expected grounded electricity supply.
replyIf you buy the UK 1.8-metre Power Adapter Extension Cable, this has a metal ground pin that grounds through the metal clip on the power brick. I switched all my MacBook & iPad chargers to this, no more earth leakage sensation from metal casing.
replyDisappointing. I understood Neo doesn't come with a power plug in UK; was yours the official one?
replyYou wouldn't have this if your plug was properly grounded. Most developed countries have plugs that have grounding. EU via side pins UK via third prong
replyMy experiences are all from third-prong countries.
replyTo add to this, I notice this more frequently in the UK and EU countries than in some other parts of the world (although it varies within each country quite a bit).
replyApple avoids shipping grounded plugs as if it was personal affront to Ive. Also caused many many times for me to be shocked with electrostatic build-up.
replyall my EU/UK macbook plugs I got from apple are always grounded, metal prong and metal side pins
replyso what I mean is maybe house electricity grid is not grounded.
UK plugs are always grounded because there is no ungrounded version.
replyBut elsewhere you only get grounded plug if you buy extra extension cord for the apple power brick, otherwise it's only ungrounded.
> all my EU/UK macbook plugs I got from apple are always grounded, metal prong and metal side pins
replyThe short version, where you remove the extension with the 3-prong plug and attach the plug directly to the charger brick, is only available in 2-prong in the EU/US (the UK thankfully still gets all 3 prongs in this configuration)
yes true the short one has no grounding.
replyAnyway as I replied to the other guy (and got downvoted for it) if the plug was grounded there would be no issue. Apple chargers have ground pins.
But sure it's bad if they stopped including grounded versions by default in EU...