Oh is that why it happens? Was wondering why the spot directly under my wrist was pitted into a sawblade. I also filed it, though just enough to remove the pitting, nothing like the OP did.

It's easy for me to feel the mains frequency while gently rubbing the top surface of the MacBook while it's plugged in. Really feels unsafe, but neither me nor the computer have suffered any serious injuries yet.

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userbinator 5 minutes ago | parent | next [-]

Really feels unsafe, but neither me nor the computer have suffered any serious injuries yet.

That's due to interference suppression capacitor in the PSU. The safety standard puts the "touch current" limit at something like 300uA (0.3mA), which is definitely in "painful but not dangerous" territory. You do need to exercise caution when plugging in other devices that are also connected to the mains, since that amount of current and voltage can certainly damage sensitive electronics.

Old but good page on such measurements: http://www.aplomb.nl/SMPS_leakage/Doc_ie.html

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normie3000 2 hours ago | parent | prev | next [-]

> It's easy for me to feel the mains frequency while gently rubbing the top surface of the MacBook

I haven't been a regular Mac user, but I've had maybe 3 work MacBooks since 2010 and I recall having this issue with all of them.

Why haven't they fixed it?

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sitharus an hour ago | parent | next [-]

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.

It 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.

	▲	robotbikes 13 minutes ago \| parent [-]
		I 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.

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msephton 2 hours ago | parent | prev [-]

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.

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ajam1507 2 hours ago | parent | prev | next [-]

Using a 3 prong extension cable on the charger will prevent this.

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imglorp 2 hours ago | parent | next [-]

How? The (US) charger's only got 2 pins so ground stays unconnected.

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BobAliceInATree 43 minutes ago | parent | next [-]

Apple sells a 3-pin extension cable

US Version: https://www.apple.com/shop/product/mw2n3ll/a/power-adapter-e...

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pxx 2 hours ago | parent | prev | next [-]

There are grounded duckheads for this purpose, e.g. https://amzn.to/4cnzuef (note out of stock. I guess your best bet is to use a UK duckhead, but half of those have a dummy ground...)

if you take the plug part from the brick you'll note that there's only two pins but the button-like thing is a ground

as noted in a sibling, the power adapter extension cable does plumb the ground through (https://www.apple.com/shop/product/mw2n3ll/a/power-adapter-e...)

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bombcar 2 hours ago | parent | prev | next [-]

I don't know if this link will work - https://www.chargerlab.com/wp-content/uploads/2022/06/202206... but that metal round pin thing is a ground; and the three-prong cable connects to it.

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Tsiklon 2 hours ago | parent | prev [-]

The extension cable they used to include in box with the computers, it has the third pin for the charger brick connector which is wired to ground

	▲	15155 2 hours ago \| parent [-]
		There's zero chance that the DC ground in the laptop is tied to earth ground in the charger: they use LLC resonant converters and flyback converters (depending on vintage) - an earth ground tie would defeat the purpose of these isolated topologies.

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CGamesPlay an hour ago | parent | prev [-]

That cuts it by about 90%. But as others have said, the default US plug doesn't ship with a ground pin (though the extended cord does IIRC).

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leptons an hour ago | parent | prev [-]

Maybe you're holding it wrong? j/k

Seriously though, that does not sound safe at all.