I have no idea why. But apple have not earthed the stubbly plug for the macbook pro transformer. So on the short lead the only way the charger is earthed is when I touch it or the macs unibody which gives you a sort of vibrating feeling on your palms.

When I went to the genius bar to complain about it they said that it was completely 'normal'. Where their definition of normal is that every MacBook does it. I have had 4 MacBooks and all have done it.

The genius did say that he though he has seen a few earthed 3pin plugs. So my question is where can I pick one up? or how could we force apple to earth the stubby plugs and recall them?


This is so commonly misunderstood that I shall attempt to provide a short précis, then link to a good explanation which is not overly-technical.

Common misconception - earthing/grounding

Most small household appliances are not, in fact, earthed at all - even if there is a valid earth pin on the mains plug.
They are what is known as 'double insulated' & carry this logo

enter image description here

The 'transformers' on this type of equipment are not the same as in high-power equipment & don't use a step-down coil transformer, linear supply. Instead they use a switch-mode supply.
All PSUs, whether linear or switch-mode leak a small amount of current due to capacitance. In double-insulated devices there is no true ground/earth so the design is optimised to try to prevent this leakage.
Unfortunately, switch-mode supplies run at very high frequencies, so the smaller capacitance in the smaller transformer ends up leaking just as much as the larger capacitance in a larger transformer running at 50 or at 60Hz for example.

The leakage current is usually less than 1mA and is often as low as 10uA, but even at such low current, it can still be present and still can cause problems.

So - the tingle or buzz that you feel is in fact you becoming the temporary ground/earth for this circuit.
It is usually safe, & any reputable manufacturer will ensure their PSUs are well within tolerance.

Cheap copies are cheap because they don't bother with most of the safety circuitry… you know, the stuff that makes the expensive one expensive in the first place ;-)

Have look at http://www.unitechelectronics.com/sparks.htm for a much more detailed explanation. Though it is aimed at hi-fi users & deals in 240v mains, the basic principles are identical.


In countries where the plugs to the mains are not earthed (or grounded to power as we say across the pond) you can buy and use a US cable that carries a third conductor for grounding/earthing and get your electrician to fit sockets or equivalent wiring past the Apple kit.

I have also seen people ground their work surface like you do in a static safe work environment. If the Mac can ground itself through the table, you won't feel the leakage voltage / current since you are no longer the best path to ground.

This tingly feeling bugs me to no end, but Apple does make adapted and cables to have a ground so you might need to use them over the standard UK kit. I'm "lightly shocked" the genius there didn't suggest more options for you.

  • Well on my home desk I use the earthed long cable so its fine, but for uni I take the shorter one as its more convient. – Andrew Nov 24 '12 at 20:47
  • You cannot use a three-conductor US cable with a MacBook Pro. The adaptor only has two input pins. – WGroleau Mar 23 '17 at 13:18
  • All MacBook Pro adapters I've seen include a metal earth and two other connectors. The MagSafe all wattages and the USB-C all wattages. I suppose the US cable won't work in other outlets, @WGroleau - is that your point? – bmike Mar 23 '17 at 14:06
  • All MacBook Pro adapters I've seen are the same MagSafe devices with an interchangeable TWO-conductor insert for the various countries' wall plugs. pcmacs.co.uk/wp-content/uploads/2016/08/… In USA land installations, normally one side of the wall plug IS earthed, but -- oh, silly me, I've been using mine without the cable for so long, I forgot the cable is not reversible like the short insert. :-). The cable won't work in other outlets, but grounded adapters are available. Sorry for the (mostly) incorrect comment! – WGroleau Mar 23 '17 at 19:08

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