Re: Notebook, Hum and Ground Lifts

"Meindert Sprang" wrote ...
"William Sommerwerck" wrote ...
> Just don't do it. Protective grounding is there for a reason!

The probability of getting a shock from a plastic-cased notebook computer
is
nil. Why? Because even if a metal point on the computer had 120V on it,
simply touching it would not produce a shock unless another part of your
body made contact with a grounded conducting surface. (Damp shoes on a
concrete floor _can_ be sufficient, by the way.)

And now I grab the firewire cable, which is already pluggen in the
ungrounded computer and touch the ground sleeve of the firewire plug with
one hand while holding the steel housing of the FireBox which happens to be
grounded via the mixer. Then what?

Then nothing. You have just stated that the computer
is un-grounded. So even if your FireBox has 230VAC
on it, no current will flow because the computer is un-
grounded and provides no return path.

Note that this is also the principle of "double insulated"
products. Note that they have 2-wire power cables.

People who claim that lifting the ground is _always_ dangerous know little
about grounding or electricity.

Like I mentioned in an earlier discussion, lifting the protective ground of
a device makes that device floating at half the mains voltage through the
caps of the power filter. Bad idea. Try it. You can feel it tingling in your
fingertips.

Thank goodness that only guitar amplifiers have this
goofy (and dangerous) arrangement. Most electrical
equipment is designed more sensibly.

.

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