My toughbook does this as well. One of the replies there says thinkpads have the same problem, and I have an IBM power adapter, so that could be the culprit. IIRC it's high frequency, so probably created by the supply itself rather than a floating neutral in the building wiring.
How can I avoid my MacBook Pro giving me minor shocks?
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Re: How can I avoid my MacBook Pro giving me minor shocks?
#12Don't use Macs but I'm surprised Apple apparently didn't give an earthed power adapter by default on a metal skin product. This seems like negligence. Now that I think about it, my iPad's the same when charging.
There's also a good chance that, at least in part due to Apple's greed and extravagant prices for chargers / fragile power cords, many people are using knockoff chargers and don't know it. See also Amazon happily selling knockoffs as real -- Apple claims 90% of chargers it recently bought on Amazon are fake and is suing the supplier, though unfortunately is not suing Amazon [1], which might help Amazon find the will…
Have you seen a tear down of the authentic chargers? There's a lot going on in there.
Re: How can I avoid my MacBook Pro giving me minor shocks?
#13My understanding is that it's caused by Y capacitors in the power supply's EMI filter leaking minimal amounts of current onto the case. As others have mentioned, proper grounding usually fixes the issue - although in one case I had to rewire an entire apartment because someone had a very lopsided idea what the PE wire is for. It was for a friend with a metal Macbook Pro, an exceptionally sensitive skin, and way too much time & money on their hands. :D
The usual word of caution: I'm trained in electrical installations. A layperson - even one skilled with a multimeter and a soldering iron - should never attempt to modify ground connections or power distribution. There are dozens of potential (and very deadly) failure modes that require proper training to recognize and prevent.
Re: How can I avoid my MacBook Pro giving me minor shocks?
#14I thought I was the only person to get shocks of my Macbook Pro, and that it had some problem. All because of the lack of a third pin.
Re: How can I avoid my MacBook Pro giving me minor shocks?
#15I have this problem in India. I suspected the mains was dodgy, because during the many power outages i never got the shocks when on UPS. I got a multimeter and measured. The neutral was 70V and the phase 300ish. So the difference was roughly 230V but a switched power adapter would make this hover around 70 too (I believe an old coil based would probably been fine). The Indian electrician didn't understand my problem…
The 70v is probably induced voltage at milliamp levels.
You can fix it by bonding the neutral to ground at the breaker box.
Re: How can I avoid my MacBook Pro giving me minor shocks?
#16I've run across this before - once I measured the shell of my MBP at 90 volts DC. If you don't have access to a 3-pin charger, you could always use a separate earthing setup, such as an antistatic mat: https://en.wikipedia.org/wiki/Antistatic_device#Antistatic_m...
90 volts above earth ground? Or relative to something else?
Re: How can I avoid my MacBook Pro giving me minor shocks?
#17Ungrounded adapter + bad mains power = zap!
Ungrounded adapter + clean mains power = probably no zap
Grounded adapter + bad mains power = probably no zap
Grounded adapter + clean mains power = no zap
It's not just the adapter and it's not just the mains power; it's when both come together. Electricity follows pretty simple rules when it comes down to it.
Always always always ground your A/C connections. Why wouldn't you?
Also, never use one of these unless you've attached the little wire/alligator terminal to a ground somewhere:
http://www.prestonelectronics.com/audio2/ttip/images/gndadap...
Re: How can I avoid my MacBook Pro giving me minor shocks?
#18What's fascinating to me about this phenomenon is that you can actually feel the 60Hz AC by running your hand across the lid.
It feels as if the surface is slightly bumpy, but the width of the bumps changes as you adjust the speed your finger moves.
Unplug from mains, and the surface becomes smooth.
As the answer notes, this only happens when using the two-prong adapter without earthing. It also seems to be more noticeable when connected to older buildings.
Re: How can I avoid my MacBook Pro giving me minor shocks?
#19FYI, I can't remember which way round it is, but only some of the UK 3-pronged adapters are actually earthed (as I discovered after having this problem myself).
I think it's the extension cord that is properly earthed, whereas just the plug attachment that goes directly into the power brick is not. You can tell by looking up into the adapter (the part that plugs into the power brick) and seeing if it's metal or plastic...
Re: How can I avoid my MacBook Pro giving me minor shocks?
#20FYI, I can't remember which way round it is, but only some of the UK 3-pronged adapters are actually earthed (as I discovered after having this problem myself).
I think it's the extension cord that is properly earthed, whereas just the plug attachment that goes directly into the power brick is not. You can tell by looking up into the adapter (the part that plugs into the power brick) and seeing if it's metal or plastic...