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My Macbook Pro charger (purchased in the US) comes with two different plug attachments, one that fits directly into the body of the charger and one with an extension cord. For some reason, the short attachment has only two prongs, while the long one has an additional ground pin. What is the function of the ground pin on the long attachment? Is it really necessary?

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The third pin is a ground pin. It is required in some countries for devices with a metal surface to prevent shocks in case of a short-circuit. Since they also delivered a plug with only two pins to you, in your country it seems to be ok to use without grounding. If you want to be absolutely on the safe side, use the three pin cable.

More info.

  • Any thoughts on why the ground pin is only used on the longer attachment? I had the vague notion it might have something to do with electrical interference over a greater distance, but I could be completely wrong. – augurar May 21 '14 at 6:21
  • Interesting point. I don't know to be honest. I only know that you don't get the two-pin plug in some EU countries, only the long wire. – traindriver May 21 '14 at 6:47
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    Good answer. Additional note: there's a common misconception that the three prong charges your machine faster. That's completely false. – njboot May 21 '14 at 9:29
  • Most chargers/adaptors make no use of the 3rd pin even if present. In the UK the 3rd pin is necessary to open the other 2 holes in the wall socket, even if it serves no other purpose on a double-insulated device. The longer wire is very likely only 2-core anyway. – Tetsujin Nov 30 '14 at 14:57

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