Re: Potentially stupid question about AC

[supertimer@aol.com (Supertimer)]

Rubywand <rubywand@swbell.net> wrote:

>Supertimer writes ...
>> 
> .... 
>> DC makes sense.
>>
>    Sort of. We have a lot of terms for electronic stuff (e.g. "electrons")
>and rules that work most of the time (like current = voltage/resistance).

Ohm's law, right?  Yep, I remember DC stuff including the
relationship between current, voltage, and resistance making
a lot of sense.  AC, on the other hand, kind of blew me.  I
mean, I read up on all this DC stuff (resistors, capacitors,
voltage drops, current, etc.) and then it turns out they behave
differently with AC.

>> So how does AC work?  I know that the current
>> alternates (back and forth) so negative and positive
>> reverses sides (either 60 or 50 times a second
>> depending on the country).
>
>     The neat attribute of AC is that you can transport power (Voltage x
>Current) long distances at a high voltage on relatively small lines. When it
>gets where you want it-- like a line going past a row of homes-- you can send
>it through a simple step-down transformer at each home to get the lower
>household voltage and a high current capability.

Yup.  Watched the history channel about Niagra Falls.
They needed the transport the electricity down to
Chicago.  Edison wanted to do it with DC, but could
not figure out how.  Westinghouse proposed AC (they
bought the patents from that Tesla fellow who invented
the AC generator...alternator).  Edison tried scare tactics
like electrocuting animals with improperly wired AC, but
Westinghouse finally won when Tesla himself passed
AC through his body and lived to tell about it.

>> I also know that if
>> electricity is leaked, in a grounded device the
>> electricity goes into a wire that leads to a post
>> that's driven deep into the ground (hence ground
>> wire).
>> 
>> 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?
> ....
>
>     Pretty much.
>
>     The more equipment you have using AC motors, transformers, and circuits
>which actually run a capacitor from AC to some chassis, the greater the
>potential for 'leakage'-- i.e. for having some capacitively coupled voltage
>that 'wants' to go to ground.   
>
>
>     From what I recall about this stuff, when the AC comes off a transformer
>to your home you usually get 220V with a center tap:
>
>
>
>S______(hot)_______________ typically Black (220V from hot to hot)*
>S
>S                110V
>S____(neutral)__________    typically White*
>S
>S                110V
>S______(hot)_______________ typically Red*
>
>
>(110V and 220V are the traditional values. The actual voltages are going to be
>closer to 115V and 230V.)
>
>     Except for 220V wiring used by some major appliances, most of your wiring
>is going to be 110V and come from a "hot" line plus "neutral". The usual color
>coding for 110V wiring is 
>
>Black-- hot*
>White-- neutral*
>Green-- an earth ground (via a grounding rod)*
>
>*WARNINGS: By the way, it is best not to place a bunch of faith in color
>coding. Not everyone follows the "usual" coding. Some wiring may reverse black
>and white.
>
>For sure, you do not want to place any faith in any 'big hole', 'little hole'
>conventions for wall sockets. Just assume they're both hot.

Ok, this is what I was originally confused about.  What is the
difference between hot and neutral if appliances run if you
reverse the leads?

And why is it dangerous to defeat a polarized plug?

>Avoid counting a lot on voltage measurements to earth ground as a guarantee of
>no shock hazard. Many meters load down the measured circuit and do not
indicate
>true voltage at small currents. Even at low currents, a decent voltage can
make
>you jump and break something.
>
>Water pipes should _not_ be counted on for use as an earth ground.
>
>     I don't know if white (neutral) is commonly tied to a grounding rod at
the
>utility pole (where the transformer is), at your home, or at either place.
Even
>if it is, you would be likely to measure some voltage from neutral at a wall
>socket to earth ground because lights, etc. on the same circuit are pulling
>current through the neutral line and your household wires are not perfect
>conductors. (That is, the neutral line on a particular socket could behave
>something like a tap on a resistor connected across a voltage.)
>
>     So, you can often get at least a small shock from touching a white
>"neutral" wire at a 110V socket if you are at all gounded. Touching the black
>"hot" wire can deliver a much more serious shock if you are at all grounded.
>Touching the black and white wires at the same time will definitely deliver a
>serious shock.

So both hot and neutral wires carry current, correct?  The
difference is that the neutral wire is also grounded (at the
unity pole where the transformer is)?  So how does the
polarized plugs work (is the something in the appliance
connected preferentially to one lead rather than the other)?

I'm asking because I used to be called to install household
fixtures for relatives and I used to always connect the wires
any which way.  I mean, polarity did not seem to matter
since the appliances always worked either way.  Now it
turns out there is a safety concern.  Why?