Re: Potentially stupid question about AC

[the.cat.in.the.hat@usa.net]

>Ok, that makes sense.  Question: why are polarized plugs
considered safetly plugs, then?  Like you said, there is no
definitive negative or positive, but some of the newer devices
have instead of a grounding prong, one prong larger than the
other so that you are physically prevented from plugging
your appliance backward.  My electric drill and my alarm
clock are this way.  The manuals say that they are "double
insulated" whatever that means but that the safety feature
only works if the polarized plugs are not defeated.  Why is
this so?  (BTW, I know the drill and alarm clock works when
connected backward, just wondering why it is dangerous
to defeat the polarized pronged plugs.) 


Not sure. I think it may have something to do with the double insulation. 
Now i am in Australia, so i may not know that much about your plugs(two 
pins?) This means that the whole appliance is insulated, so if a surge or 
something occurs a spark cannot leap out of the appliance itself and onto 
the nearest ground path. This means that any sparking is contained to the 
plug.  So if a spark occurs it may jump from live-neut and possibly fry 
your electricity wiring. The troughs may line up with the peaks and the 
waveform may end up looking like this:

| /~\  /~\
|/   \/   \
-------------------------
|\   /\   /
| \_/  \_/

(as i said i am very unsure of this) Rectifiers are not designed to filter 
this kind of waveform, probably blowing the power supply.
There is less chance of a major problem if the polarization is correct, 
because a circuit is being completed. Because AC is a sine wave, meeting 
up with another which peaks and troughs line up will make a standing 
wave....Or it may be just a big conspiracy theory. I can't really answer 
that, sorry. You have me there.


>But AC is self contained, right?  That is, the negative and
positive are reversing in the two wires (live and neutral)
themselves, so where does the ground fit into the balance?

Purely for safety purposes. Voltage is only related to pos and neg.