
Electrovibration in Ungrounded MacBook Pros - jakerockland
https://blog.somaticlabs.io/electrovibration-in-ungrounded-macbook-pros/
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gaur
Trying to power a metal-shelled computer with a 2-prong plug always seemed to
me like an example of Apple painting themselves into a corner. The only two
options as far as I know are to leave the case floating (which seems bad) or
to tie it to the outlet's neutral pin (less bad, but still not great). The
latter presumably leaves you at the mercy of how well the building's neutral
pins are grounded. The fact that Apple decided to use fairly puny wires
between the power brick and the computer probably doesn't help either.

[Also, the link on electrovibration seems to imply it's a capacitive effect,
so it's caused by an electric (not magnetic) field.]

~~~
aexaey
First option (ground floating) is actually quite common:

A Class II or double insulated electrical appliance is one which has been
designed in such a way that it does not require a safety connection to
electrical earth (ground). [1]

[1]
[https://en.wikipedia.org/wiki/Appliance_classes#Class_II](https://en.wikipedia.org/wiki/Appliance_classes#Class_II)

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aexaey
Two small nits about second part of this passage:

    
    
      electrovibration — the rapid attraction and
      repulsion of the skin to an insulated ground
      plane (such as brushed aluminum)
    

\- Metal in unibody MBPs is sandblasted [1] rather than brushed [2] to give it
its texture;

\- Neither sandblasting nor brushing aluminum gives it thick enough oxide
layer (Al2O3), and it is that layer that makes actual insulation. Instead this
layer is formed by the way of anodizing [3], complementary and separate
process.

[1]
[https://en.wikipedia.org/wiki/Abrasive_blasting](https://en.wikipedia.org/wiki/Abrasive_blasting)

[2]
[https://en.wikipedia.org/wiki/Brushed_metal](https://en.wikipedia.org/wiki/Brushed_metal)

[3]
[https://en.wikipedia.org/wiki/Anodizing](https://en.wikipedia.org/wiki/Anodizing)

------
andreiw
Experienced same with an iPhone 5s and a three-prong Belkin charger in a
Puerto Rico rental.

Scared the hell out of me, too. Brushing the metallic back I'd feel sticking.
I think I licked it too, and it felt sour.

