Hi Tom.
>>>
Isn't it the difference in electrical potential between the components
(including the human) what counts as far as the computer parts are
concerned?
Yes.
>>>
As I understand it, grounding merely lowers the potential to zero, ...
The difference in potential. It's all relative. There is no absolute
reference. We normally assume that "ground" (the earth's ground) is the
reference, hence the term "grounded". But there is potential difference
between different parts of the earth, too!
This is why a good audio system will ground the shields of cables at only
one end, else they pick up "ground noise" (mostly 60 cycle "hum" from the
power distribution system). Even running a coax cable between buildings is
dangerous because of the "ground inbalance", especially during a storm!
Equipment is generally "grounded" for safety because most of the time when
someone comes in contact with a piece of equipment, they complete a circuit
to "ground", not some other potential. So if both sides of the person are
at "ground potential" there is no current flow through the person.
It's the current flow that kills you, not the potential difference, by the
way. Of course, for a fixed resistance, the more the potential difference
the more the current flow. Hence those physics lab 100KV generators which
just make your hair stand up.
With electronics, either current or voltage can damage a component,
depending on the type of component. Static electricity doesn't normally
generate a lot of current but it can easily generate 1K to 100K volts! CMOS
IC's are particularly susceptible to damage from voltages as low as 10
volts.
So, the important thing is for you to be at the same potential as the case.
Using a wrist strap to earth ground while the case is "floating" (not
plugged in) does help, because it limits your potential difference from
earth ground, but there is nothing limiting the case's potential difference
from ground. So you still have a potential problem. [pun intended!]
John
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Received on 07/03/03
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