Re: AC/voltage basic physics questions, please.


<srp2inc@xxxxxxxxx> wrote in message
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On 29 jan, 09:38, "Ockham" <m...@xxxxxxxxxxxxxxxxxx> wrote:
<srp2...@xxxxxxxxx> wrote in message

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On 28 jan, 22:40, HC <hboo...@xxxxxxx> wrote:



Folks, this is probably so basic as to be silly but it's something I
have not found a concise answer to yet, so please bear with me. I
think this is the right group to ask because what I'm wanting to know
is how electricity works, in my particular questions, at a low level;
I'm thinking along the lines of actual electron flow. Your help is
appreciated.

I live in the US and what's bugging me is trying to understand what is
going on with 120v AC that we have from our standard household
outlets. I understand some basic stuff about electricity (like that
electrons move through conductors, the atomic layout of materials
(protons/neutrons in the nucleus, electrons in a cloud around that))
and so forth. Really basic stuff. What's still eluding my
understanding is what's going on at a low-level with 120v AC? I mean,
I replaced the breaker box in my home myself; I wired my shop with
both 120v and 240v AC and put in outlets, lights, and the breaker box,
too, so I can work with the stuff, but that got me a close look at
some things I don't understand:

First, the power that comes in from the utility transformer comes
across three wires; two "hots" and a "ground" or "neutral". In my
breaker box I have tied the neutral to the ground;

| Something strikes me as odd here. In our place (I live in Canada,
| same 120-240 VAC setup) neutral is NOT connected to ground.

Correct. The reason is this.
Suppose that an appliance has developed a fault, say a vacuum
cleaner has worn its brushes and carbon dust has spread, leaving
a conductive path to ground and some current is passing along
the ground wire through the plug and socket when it should only
pass through the neutral. Now further suppose that the neutral
wire becomes disconnected (very possible when amateurs
do the wiring), and the return path is through the ground.
The little old lady touches the metal work of the cleaner and gets
a tingle. Some people are very sensitive to shock and she has
a heart attack. Big law suit. Solution: fit an earth leakage trip
(aka ground fault protector).
A tiny current in the ground wire and bingo, the supply is switched
off.

| The box and all outlets are connected to the ground bar that goes
| into the earth, but the return common (neutral) is not connected
| to it.

Right.

| All outlets have three wires ground (naked copper), common
| (white insulation) and live (black insulation). We are warned never
| to connect the common to ground.

Correct. Not everyone knows the black is hot and the white cold.
In Britain it used to be red for hot (line) and black for cold (neutral)
with green for ground (earth) but that changed to a different standard
with brown hot, blue cold and yellow/green for earth (ground).

That would be some normalized European standard then, because
I know that this last code is standard in France and Germany. (We
ship material over there with this mandatory standard)

To bad they didn't go for the British standard, which seemed to
make more logical sense (to me, anyway).

André Michaud

http://tinyurl.com/2adahn

http://www.niceic.com/17thedition/nroot/niceic/17thedition/majorchanges

The 17th Edition of the Wiring Regulations is due to be published on 1st
January 2008 and expected to come into effect after a six month transition
period. In this section we examine the potential changes.

Some electrical contractors may ask why we need another Edition of the
Wiring Regulations. This is a fair question, considering the amount of
reprints and amendments over the years. You might think that, to date, there
have only been three editions of the Wiring Regulations since the 14th
Edition was published in 1966.

However, consider this: Although the 14th Edition was issued in 1966, it was
reprinted in 1968, 1969, 1970, 1972, 1973, 1974 and 1976. The 15th Edition
was issued in 1981 but reprinted in 1983, 1984, 1986, 1987 and 1988.
Finally, the 16th Edition was issued in 1991, but reprinted in 1992, 1994,
1997 and 2004 too!

A combination of new technologies, products and continuing harmonization
mean that the Wiring Regulations have to incorporate changes such as these;
and we can expect no let up in this progress as time goes by.
-------------------------------------

Some day they'll have computerized plugs on appliances to do
everything; circuit breaker, earth leakage protector, license checker,
rain gauge, temperature readout, credit card swipe, big brother spy
camera, everything you can think of except work properly.

.

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