My wife and I both have MBP's and sit on the couch working with our laptops in our laps. WHenever our elbows touch, we get very painful shocks. Not quick static shocks, but more constant current shocks. We're plugged into the same wall and both using grounded plugs, you would think on the same ground. I'm trying to determine if one of our MBP's are shoring someone on the unibody but don't have a DVM here. Trying to bring one home later this week. Anyone have ideas or know of an issue ?
"This has the potential to be dangerous, folks. It takes less than one amp across the heart to kill a human."
As you've noted, a properly grounded computer solves the problem. The current is on the cover is measured milliamps, well within international standards, and is not a safety issue.
@carl - I believe that the amperage associated with the problem is not enough to be lethal but I sit here in Stuttgart, Germany with 2 of my fingers and half my left hand "asleep" for the past few months. I believe strongly that prolonged lower voltage can be dangerous to nerves. I'm hoping this sensation goes away on it's own over time as I have now removed the source of the irritant. That would be in my case the 2 prong adaptor. It shocks in all cases in every building it is plugged into so I know it has nothing to do with proper grounding which can't be supplied through 2 conductors anyway.
It is a danger that sneaks up but a danger none the less. I wish it would have bit me hard.
...I have now removed the source of the irritant. That would be in my case the 2 prong adaptor. It shocks in all cases in every building it is plugged into so I know it has nothing to do with proper grounding which can't be supplied through 2 conductors anyway.
Your logic escapes me. You get shocked whenever and wherever you use the non-grounding plug and you don't get shocked when you use the grounding plug. And from this you've concluded that the shocks have nothing to do with proper grounding?
sonny, I can understand your concerns about your hand, but have you seen a "carpal tunnel" syndrome expert about this?
My wife suffered this long ago (before even the Apple Mac had arrived on the scene, in the days when desktop computers were in their infancy and electric typewriters ruled the world) and her symptoms were identical to those you report. See h
http://www.abc.net.au/health/thepulse/stories/2008/10/16/2374239.htm for a description of symptoms.
@Rod Hagen- Thanks Rod and I have not been to an "expert" yet with this. I did however ask my regular doctor specifically about carpal tunnel and I was told that this would not be in the 2 fingers in question. I will have this reevaluated though as he is not an expert.
@eww- The small adaptor has 2 pins. These apparently are not always effective in grounding the aluminum case on the MBP. The big cable has 3 conductors which obviously must encapsulate and carry a ground. In MY particular case this cable corrects the shocking problem not prevented by the 2 prong adaptor. If someone chooses to use the 2 pin adaptor they are taking a risk. This is only my opinion. If you use the big and not very stylish or convenient cable; your safe in my experience at least with MY MBP. I'm proclaiming a warning to use the big cable though it may be inconvenient and steer clear of the 2 prong adaptor even if you don't feel an uncomfortable shock. Most mass produced products including complex electronics will share similar traits. It's proof that quality controls are in place and work well. This thread along with others bears this out. If you want to tell people to continue to use the 2 prong adaptor knowing everything being discussed here; I openly question your motives. Saying the wiring in peoples homes is defective will not prove factual in many cases and you should reconsider claiming this as it shows ignorance and arrogance. Does my logic escape you still?
Your logic is faulty, and the facts have escaped you. At no time have I ever urged anyone with this shocking problem to use their 2-prong adapter, precisely because it can't provide the ground that is necessary to eliminate that problem. But even using the three-prong cord won't eliminate the problem if the outlet being used, or all the wiring in the building, is not properly grounded. In a number of cases, people have posted back to acknowledge that they found their building wiring to be faulty after being urged to check it. Urging them to check it does not "show ignorance and arrogance;" it shows awareness of a possible cause of their problem that they may not have considered — which, in most cases, is exactly what they were seeking when they posted here.
I wonder if this isn't even a real "voltage" issue. Maybe it is a very low power corona discharge. All electrical devices emit a magnetic field; put a (dead) wire close to it and there will be a slight current.
The field produced by the machine may be enough to charge the Aluminum case to the point where it can be felt by mere mortals.
If the power leads came into contact with the metal case; it would short out and the machine would be toast. Right?
I’ve had my MBP 17” for a month now, I brought it in the US but live in the UK so have no choice but to use a three prong plug. I have been experiencing current feeling shocks from the right angle edges of my MBP. The problem is intermittent and I think only occurs when it’s connected to the power supply and fully charged.
"Maybe it is a very low power corona discharge."
"Low-power" and "corona discharge" are mutually exclusive. A corona discharge is caused by very high, not very low, voltage.
"All electrical devices emit a magnetic field; put a (dead) wire close to it and there will be a slight current. The field produced by the machine may be enough to charge the Aluminum case to the point where it can be felt by mere mortals."
The induced voltage will be VERY low. The voltage on the metal case is "high", between 60 and 120VAC, depending upon the AC input voltage.
"If the power leads came into contact with the metal case; it would short out and the machine would be toast. Right? "
It depends. The AC voltage is INTENTIONALLY placed onto the computer chassis. It's done on purpose. That's the way it is designed. If the DC voltage was placed onto the computer chassis, the power adapter would shut down: it has both over-voltage and over-current protection circuitry.
I may be able to add a little something to this thread. And then again, maybe not. 🙂
I'm an electronics engineer (embedded systems designer) and I've designed in and worked with AC adapters like the ones supplied with the MBP. Although I've never cracked a MacBook adapter open to see what's inside, I have a very good idea. They should be pretty much like all the rest. The adapter is what's called a switching regulator. It takes the 120vAC, rectifies it to produce 160v DC, then using electronic switches, it chops that DC voltage into a high frequency AC voltage (much higher than 60Hz). This high frequency AC voltage is then applied to a transformer that steps the voltage down to around 5 volts (or whatever) and sends that low voltage on to the device. They go to all this trouble because a transformer can be made very small if it is transforming a high frequency voltage (vs the 60 Hz you get straight from the wall). It is also very efficient, so everything can be made much much smaller than a regular wall wart. So far so good. But to comply with UL and FCC certification with regards to EMI (electromagnetic interference), every one that I've seen also has a small value capacitor connecting one side of the 120vAC line to the ground side of the low voltage going to the device. Now, I've never designed a switching regulator type adapter that had to go through UL & FCC, so I don't fully have a grasp on why this is done. But it continues to surprise me that it's there. Seems dangerous. They are actually coupling a small voltage/current from one side of the mains to your device. Depending on which way you have the adapter plugged in, that one side may be the hot side (high voltage) or the neutral side (low voltage).
If I plug my MacBook's adapter in one way, I measure 47 vAC from its case to the earth ground of the receptacle. If I turn the adapter around so that the prongs are reversed, I measure only 2 vAC. In one case that stupid little capacitor is connected to the hot side, and in the other case it's connected to neutral. By the way, 47vAC actually contains peak voltages of 66 volts. That's probably enough for most people to feel, especially through sweaty hands, and depending on how good of a connection to earth ground you have with other parts of your body.
Most capacitors that I've seen used are very small in value, meaning they cannot conduct much current without the voltage being reduced accordingly. It's the current that the body feels... it's the voltage that pushes the current through you. In other words, it's not going to kill ya.
But there is one more aspect that may explain why some people are getting quite a jolt and others get just a tingle (or none at all). That capacitor gets better and better at coupling voltage through it as the frequency of the voltage increases. At 60Hz it's just so much. But any "spike" of voltage on the line (which by definition is a high frequency) is coupled through it quite well. If you have some motor or other device on the same power line that is inducing transient voltage spikes then those high voltages will get to you much better than the 60Hz voltage will. May explain why in some situations it is worse than others.
My suggestion is to never ever lick your MacBook while standing in water. 🙂 Seriously, if you're experiencing this just turn your adapter around and make a mark on it so next time you know which way to plug it in.
"I don't fully have a grasp on why this is done."
The voltage leakage attenuates the emitted RFI, and allows the computer to comply with FCC class B regulations.
"Seems dangerous."
It is not. The current level is very low, well within international safety standards.
