I shocked my partner with my computer. Why?
October 3, 2014 5:16 PM   Subscribe

I was sitting in bed with my laptop about an hour ago. When I reached out to tap my partner's arm, we both felt a buzzing, dragging feeling - like touching the handle of a turned-on electric razor or something - and pulled back from each other. This only ever happens with MY laptop, regardless of what my partner is doing/holding/touching.

I suspect that part of my problem is that my 19V adapter uses a 2-pronged plug. It's my second adapter replacement after burning through the one Asus gave me. On the other hand, I'm also slowly watching a couple of USB ports stop working, and my headphone jack's been long gone. But my laptop has otherwise been remarkably reliable since 2009, and I was hoping to squeeze as much life out of it as possible until I could afford a new one.

Is this a motherboard issue, or something else? Is there anything I can do to reduce the amount of exposure, or should I stop using this laptop?
posted by Ashen to Computers & Internet (16 answers total) 1 user marked this as a favorite
 
power is somehow leaking out from the innards to the case of your machine. i think a proper 3-prong plug would solve your problem, but you should figure out what it is before you get electrocuted.
posted by bruce at 5:37 PM on October 3, 2014


Don't leave your laptop plugged in while you are not using it.

It could start a fire.

Ask me how I know!
posted by jbenben at 5:54 PM on October 3, 2014 [1 favorite]


My MacBook Air does the same thing! It's been at least two years since I first noticed it, exactly as you did, while touching my partner's arm. It only happens when it's plugged in. I'm using the original power cord it came with, too. I personally have no concerns about continuing to use the laptop, for what that's worth.
posted by lizzicide at 5:56 PM on October 3, 2014


It's also a common complaint from other MacBook users, with people chalking it up to the 2-prong cord design... Do some digging and see if this has also been reported widely among Asus users.
posted by lizzicide at 5:59 PM on October 3, 2014 [1 favorite]


What you're describing sounds like an AC shock from line current leakage.

Were you yourself touching any metal part of the laptop case, the power cable, anything connnected to any of the ports, or anything of the kind? What other conductive objects might you have been touching? Plastic doesn't conduct enough electrictity to shock you, and neither should any normal bedsheets. Bed FRAMES might.

Did you feel anything at the point where you were touching the laptop, or only where you were touching your partner?

It doesn't make a lot of sense that you'd get a shock if your partner wasn't either grounded or touching something that was itself "electrified". Are you sure about that part? Does it only happen in bed? If not, where else does it happen?

Most AC adapters are isolated, and in fact doubly isolated. That means that there simply shouldn't be "shock-worthy" power OR a ground path at the laptop itself. Neither the motherboard nor the case of your laptop should have access to any dangerous voltage.

Which means that, if the voltage is coming through the laptop, and unless your laptop is a very unusual design indeed, your AC adapter is bad. Other things may also be bad (including possibly a miswired outlet) but that almost has to be bad if it's not a very weird system.

Is it an original Asus adapter, or is it a cheap off-brand replacement? The cheap ones are notorious for cutting corners on safety features. What does it say on the label of the adapter? Does it claim to be UL listed? Does it give a UL power supply class?

A three-prong plug is used to ground out a metal chassis. The idea is that any shockworthy voltage will be conducted to ground, and if there's enough leakage to produce significant current, it'll also trip a circuit breaker somewhere. Normally that third-prong safety ground would NOT be continued from an AC adapter to a laptop; it would perhaps connect to a metal shield inside the adapter, but that's as far as it'd go.

Consumer electronics are not supposed to give you shocks, even if it's widely reported.
posted by Hizonner at 6:05 PM on October 3, 2014 [2 favorites]


Hmm. I have to correct myself slightly. Apparently those power supplies are allowed to leak enough current that you can feel it. http://www.epanorama.net/newepa/2012/04/02/isolated-laptop-power-supply-issues/.

But they definitely shouldn't be leaking enough that it's a serious painful shocking sensation. And it should be less if your adapter is plugged in with the right polarity. Do you have a polarized plug? If so, are you sure your outlet is wired right? If not, what happens if you flip the plug over?
posted by Hizonner at 6:21 PM on October 3, 2014


This used to happen with my Titanium Powerbook a decade ago. I'm not sure I remember the circumstances - probably when I used a two-prong plug instead of a three-prong grounded plug (my charger extension and my brother's iBook's extension sometimes got swapped). I could run my hand across the titanium case and feel that slight, intermittent "vibration".
posted by WasabiFlux at 7:00 PM on October 3, 2014


her partner here. it's not a painful shock, it's more of like what you might feel from static electricity. the real problem is that if I touch her, I can feel the buzz of current on contact which is very weird.
posted by Ashen at 9:21 PM on October 3, 2014 [1 favorite]


the real problem is that if I touch her, I can feel the buzz of current on contact which is very weird.

I get this when I touch my partner's arm when he is using his laptop. It's been that way for years and fwiw so far neither of us is a cyborg.
posted by DarlingBri at 9:31 PM on October 3, 2014 [1 favorite]


To answer you, Hizonner:

Were you yourself touching any metal part of the laptop case, the power cable, anything connnected to any of the ports, or anything of the kind? What other conductive objects might you have been touching? Plastic doesn't conduct enough electrictity to shock you, and neither should any normal bedsheets. Bed FRAMES might.

Hmmm. I may have had one of my hands near the ports themselves. I hold my laptop in weird ways for support if I'm casually browsing.

Did you feel anything at the point where you were touching the laptop, or only where you were touching your partner?

Only when I touch my partner do I feel anything.

It doesn't make a lot of sense that you'd get a shock if your partner wasn't either grounded or touching something that was itself "electrified". Are you sure about that part? Does it only happen in bed? If not, where else does it happen?

It's happened in our living room several times, but I don't recall what they might've been touching at the moment.

Is it an original Asus adapter, or is it a cheap off-brand replacement? The cheap ones are notorious for cutting corners on safety features. What does it say on the label of the adapter? Does it claim to be UL listed? Does it give a UL power supply class?

It was a (fairly) cheap Enercell replacement. I don't see a UL power supply class listed. Even though this one hasn't burnt out like its predecessor in under 6 months, you're right: it's a bad adapter. Looks like I'll be shopping for a new one!

Thank you for your responses, everyone!
posted by Ashen at 10:19 PM on October 3, 2014


The typical AC adapter has a small capacitor between AC neutral and DC ground which is necessary to reduce the transmission of undesired high frequency common mode electromagnetic interference on the AC lines. This capacitor passes a very small AC current, a fraction of a milliamp, that can cause a slight tingling sensation.

It is not unsafe. It is a normal condition and permitted by safety regulations as a necessary annoyance to reduce interference noise. By the way, for medical equipment the leakage current requirements are even more stringent.
posted by JackFlash at 11:02 PM on October 3, 2014 [3 favorites]


Yes, the leakage through that capacitor is what the link in my second post was talking about. So we've converged on some kind of Truth(TM). And if it's not actually painful, then that's probably it and I have to retract my alarmism. :-)

It's still very surprising to me that there's enough current to detect. If you feel it when you touch somebody who's not grounded, the only place for the current to be flowing is into the capacitance between that person and ground. That's got to be a very, very small current at 50 or 60 hertz. And if you're not touching a metal part of the laptop, that means it has to be capacitively coupled AGAIN, across a bunch of plastic.

I know that I would never notice that kind of current, and never have even after handling tons of electronics. I guess I can believe that some people could. I find it surprising, though, that anybody would notice it without really trying to pay attention to it.
posted by Hizonner at 6:07 AM on October 4, 2014


Oh, and I'd still try turning the plug over if it's not polarized.
posted by Hizonner at 6:07 AM on October 4, 2014


Could this indicate a problem with the house wiring? An outlet with reversed polarity, or something?
posted by Good Brain at 10:03 AM on October 4, 2014


There was a question back in 2010 about a very similar issue:
Curious also that I only started noticing this in the last year and a half or so, but it's totally the same thing others here are describing... a slipping, catching. quickly vibrating feeling when I lightly draw my fingers across certain plugged-in metal surfaces. (Except for the situation where I felt it on my girlfriend's arm while I was touching my plugged-in aluminum MacBook).
Do you or your partner by any chance have asthma or severe allergies?
posted by jamjam at 10:13 AM on October 4, 2014


I don't know anything about line leakage or electronics. I did once have a used PA which started giving people shocks on the microphone and a USB audio interface connected with a 3.5mm jack had its innards.. exploded. Then my electrician friend opened it up and replaced a bit of ceramics insulation which would prevent such things. With laptops it's probably fine but with stereos or anything else with high voltage inside I'd be very careful.
posted by yoHighness at 6:32 AM on October 5, 2014


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