At 5:55 PM -0500 7/6/01, Peter Graening wrote:
>Everyone is talking about these adapters being cool - but the problem is the
>ones that Apple is recalling don't have a grounding plug. Check and see -
>all of the adapters for PPC PowerBooks that I have seen have come with a
>grounding plug somewhere on the plug - and even if this grounding isn't
>transferred to the computer - it could have some function in the adapter's
>circuits. As far as I recall, it's not safe to use a piece of electronics
>without a proper ground - even laptops. Perhaps someone on the list knows
>more about this and could elaborate on this for me.
There are two reasons for a grounded plug. The reason grounding was
first done is to protect against electrical shock. Whether a device
is grounded depends on a lot of things but mostly on the likely hood
of a fault developing which could cause an electric shock. A
computer really doesn't need grounding for this reason, it's as
likely to get a hazardous fault as a stereo component.
The other reason is to provide a common ground between all
components. Without this some parts could have excessive noise
injected into interfaces causing problems.
A laptop's power supply is usually a separate unit (a brick or wall
wart). These don't need grounding for safety reasons (most other
wall warts don't have a ground). Most of the interfaces a laptop
uses are less sensitive to ground differences. Phone, Ethernet are
both fairly well isolated. I don't know about USB or Firewire but
they are probably too.
A laptop's power supply really doesn't need a ground. Some have it
but that's more a decision by the designers. One reason to NOT have
a ground is that laptops are frequently used where there isn't a
ground.
BTW, I'm an Electronic Engineer with a reasonable understanding of
the NEC (National Electrical Code).
Barring a major fault a lack of ground would not cause overheating.
--
Clark Martin
Macintosh Consultant
Another designated driver on the Information Super Highway
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