Re: Potentially stupid question about AC

[supertimer@aol.com (Supertimer)]

the.cat.in.the.hat@usa.net wrote:

>>So why is one lead considered "live" and the other
>>"neutral" if they seem for all intents and purposes
>>to be the same.  You can plug something in
>>backward and it'll still work.  Also, why does the
>>electricity go into the ground if it leaks from a
>>grounded device?  Does the earth and the power
>>station form a circuit or something?
>
>The reason why you can plug in something backwards and it will still work 
>is as follows:
>
>Because the waveform oscillates, that is, positive voltage decreasing to 
>negative voltage and vice versa, there is really no definite positive or 
>negative. And since the regulators that change AC to DC (no appliance 
>except bulbs and heaters can run on AC (and see below*)), don't depend on 
>a positive or negative, you can plug something in backwards and it will 
>still run
>
>The reason why one lead is considered live and the other neutral is as 
>follows:
>
>As before, there is no positive or negative. Look at this diagram (or 
>convert to Courier or monospaced font if it looks wrong
>
>-----LIVE-----+   +-----NEUTRAL----
>             l|   |n
>             ---------
>            |APPLIANCE|
>             ---------
>
>Connected properly, it would work fine. The circuit is completed. Voltage 
>is running to the appliance and is running out of it just fine.
>
>Consider this
>-----LIVE-----+   +-----NEUTRAL-----
>               \  /
>                 X -live and neutral do not touch
>                / \
>              l|  |n
>              ---------
>             |APPLIANCE|
>              ---------
>Since there is no definitive positive and negative for AC, the thing still 
>runs. The circut is completed. Voltage is running to the appliance and is 
>running out of it just fine.
>
>Also possibly it is just to define which pin on your plug is which, but 
>more likely, it is the voltage straight from the supply, which current has 
>not been subtracted from, the pure 15A 240V (your area may differ) from 
>your supply.

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.)

>The reason why electricity flows to ground is as follows:
>
>Like lightning, electricity always tries to find the easiest path to 
>ground as possible. One of Nature's law is to always maintain an 
>equilibrium. Electricity is the stuff that tries to make an equilibrium 
>between + and -.  If a short is in a household circuit, say, at the plug, 
>the easiest way to ground is through the ground pin. This is a safety 
>measure for faulty plugs.
>
>I hope this has not been to technical and you can understand this. Please 
>let me know.
>
>I am only 14 but have a firm grasp on electricity and physics

Hey, that's pretty good.

I understand lighting tries to reach the ground because the
friction between the air and the ground causes a static
charge to build up.

Ok, but that's obviously balance.  Where the static charge
is an imbalance, the electrons want to go from the ground
back to the sky and zap, lightning.

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?

Second, if this rule DOES apply to AC, why does it not
apply to batteries (DC)?  If I place some batteries on the
ground (or connect either terminal to the ground socket of
an AC plug) they do not discharge.