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Why Aren't Laptop Computers Grounded?

SkeptiChick said:
You mean tetany, not tetanus.
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I'm not so sure. It seems like most of the online references for either tetany or tetanus take a solid medical perspective (where the former is calcium related and the latter, bacterial) for muscle contraction conditions. Wikipedia seems a bit broader than most for tetany by admitting "or other conditions". The "other conditions" certainly could be electrical shock.

The couple of dictionaries I tried tended towards the opposite. Tetany was solidly a medical condition related to abnormal calcium metabolism while tetanus could be more than just "lock jaw."

Bottom line: I'm confused and will admit it.
:confused:
 
Wowbagger said:
Which responses seemed particularly ignorant, to you?
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Too many to choose from. I'll let you select them given that A/ anyone should know a laptop is not only not grounded, but is explicitly isolated from the power ground B/ a power ground isn't needed for a static discharge.

Repeating what others had stated, in different words.... is addressing verbosity.... how exactly?
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Munford's explanation wasn't up before I started. The others preceding are rubbish.
 
stevea said:
Too many to choose from. I'll let you select them given that A/ anyone should know a laptop is not only not grounded, but is explicitly isolated from the power ground B/ a power ground isn't needed for a static discharge.
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Why should 'anyone' know this?

Do you include people who have never seen a computer of any description? 6-month-old babies?


stevea said:
Munford's explanation wasn't up before I started. The others preceding are rubbish.
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The lack of specific examples makes it seem that you might not have any. If you do, then at this stage, you'd better make them really, really good ones.
 
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BobTheDonkey said:
Solving for the current flow of 19V at 1000ohms (wet skin), we use I = V/R > I = 19/1000 > I = 19mA. Not near enough for a lethal dose, so on that point I concede. My power supply would not be able to kill a human (unless you used it to bludgeon someone with or the voltage regulator goes bad).
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Freaking hell. I go into detail about how that statistic is wrong and you still botch it up. Cut skin has a resistance of zero ohm's!!!!!!!!!! And its also a stupid metric. Given that my grandpa's pacemaker battery is capable of stopping my grandpa's heart and remains operational for about two years and is only the size of a hearing aide battery something is wrong with your logic. My grandpa would be dead if it was solely current that kills.
Why should 'anyone' know this?

Do you include people who have never seen a computer of any description? 6-month-old babies?
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Most newer power supplies for any electronics are two prong which lock stop and cocks a shotgun at the argument. Also, anyone who has done basic electrical work would know that the third prong doesn't do what the op or many people for that matter think it does.
 
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technoextreme said:
Freaking hell. I go into detail about how that statistic is wrong and you still botch it up. Cut skin has a resistance of zero ohm's!!!!!!!!!!
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Oh rly?


technoextreme said:
And its also a stupid metric. Given that my grandpa's pacemaker battery is capable of stopping my grandpa's heart and remains operational for about two years and is only the size of a hearing aide battery something is wrong with your logic. My grandpa would be dead if it was solely current that kills.
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I rather think the consensus is that you can't have current without voltage and saying that one or the other will kill you is a nonsense statement.


technoextreme said:
Most newer power supplies for any electronics are two prong which lock stop and cocks a shotgun at the argument. Also, anyone who has done basic electrical work would know that the third prong doesn't do what the op or many people for that matter think it does.
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That's why people come here and ask questions.

Works well, doesn't it?
 
jsfisher said:
I'm not so sure. It seems like most of the online references for either tetany or tetanus take a solid medical perspective (where the former is calcium related and the latter, bacterial) for muscle contraction conditions. Wikipedia seems a bit broader than most for tetany by admitting "or other conditions". The "other conditions" certainly could be electrical shock.

The couple of dictionaries I tried tended towards the opposite. Tetany was solidly a medical condition related to abnormal calcium metabolism while tetanus could be more than just "lock jaw."

Bottom line: I'm confused and will admit it.
:confused:
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Personally, I go with the CDC. I linked Wiki because it is generally more understandable, and in this case I knew it to be pretty correct (even if it didn't go into great detail).

Tetanus is the name of a disease which is caused by bacteria (C. tetani, aka "tetanus bacillus"), for which most people in developed countries are vaccinated against regularly. http://wwwnc.cdc.gov/travel/yellowbook/2010/chapter-2/tetanus.aspx

Tetany is a medical sign in which the patient's muscles contract involuntarily. The most common cause is a calcium imbalance/lack. There are other causes, but those are either much more rare, or only occur in non-humans (cows, for example, have their own version of tetany). I'd link a definition from the CDC, except the CDC assumes readers already know the definition, so don't provide one. If you search the CDC site for it though, you'll get a big long list of results where it is a symptom of a larger disease/condition. You cannot vaccinate against tetany.

Neither one is technically applicable to the situation, as you're talking about a muscle spasm caused by an electric shock and not a disease or a symptom of a disease. But tetany is much closer to describing the results of an electric shock than tetanus is.
 
BobTheDonkey said:
how many amps is that hearing aide battery?

Here's a few examples of your pleasure:

A 9V battery has 500-800mAh (that means 500-800mA over an hour)
A AAA battery has 1150mAh (that means 1150mA over an hour)
A AA battery has 2850mAh (that means 2850mA over an hour)

All very low current. I would expect a hearing aid battery to be somewhere lower than the 9V...of course it can't kill you, the amps aren't there.
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Milliampere hours are not a measurement of how much current a battery can deliver, they’re a measurement of how much energy it stores (which is not relevant to this discussion). For example, in theory, a perfect 2000 mAh battery could deliver 8000 mA for fifteen minutes (or, say, 1000mA for two hours) before being drained.

The current a real battery can deliver is limited by other factors, which in circuit theory is represented by “internal resistance”.

For the sake of experiment a few years ago, I momentarily shorted a 2500 mAh AA cell through my multimeter. It read about 1800 mA.
 
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I just measured my laptop power supply (which does have a "earth" pin), and the output voltage 0V is actually connected to the mains earth. That means the laptop's USB port etc are also connected to mains earth, just as for desktop computers.

This is better than my previous laptop, which didn't have an earth pin, and which would sometimes give me a very small "tingle" when I touched the output connector when standing on tiles. This was due to capacitive coupling in the power supply injecting a small 50Hz voltage on the output connector (ie, it was NOT due to static electricity).
 
MichaelN said:
I just measured my laptop power supply (which does have a "earth" pin), and the output voltage 0V is actually connected to the mains earth. That means the laptop's USB port etc are also connected to mains earth, just as for desktop computers.

This is better than my previous laptop, which didn't have an earth pin, and which would sometimes give me a very small "tingle" when I touched the output connector when standing on tiles. This was due to capacitive coupling in the power supply injecting a small 50Hz voltage on the output connector (ie, it was NOT due to static electricity).
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Yup, that sounds about right. I've got a few bricks and other power supplies that are earthed through the mains plug. Especially older transformer types.

You've reminded me of something else too.

I wonder how many non-sparky people realise that Earth isn't as 'low' as a voltage can get, and that in fact a lot of equipment has a negative rail that's 'below' Earth.
 
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I think we might be risking modulation here.

In seriousness, I can't think of anything else to add that might assist the OP, but I'm happy to clarify anything I might have said. A bit of general electrical knowledge is a good thing for everyone to have, I reckon. 'tis dangerous stuff, as much as I love it.
 
Akhenaten said:
That's why people come here and ask questions.

Works well, doesn't it?
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Not when BobTheDonkey keeps on giving out information that can get people killed.
I wonder how many non-sparky people realise that Earth isn't as 'low' as a voltage can get, and that in fact a lot of equipment has a negative rail that's 'below' Earth.
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Thats because most people don't realize that ground is what ever you define it to be. I can define a ground point to have a potential of 1000V in relation to earth ground. It doesn't matter at that point its 0V.
 
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