I have always been puzzled by the fact that even though Alternating
Current is delivered to a house, we consider one wire, usually the
black wire, "hot" and white wire "neutral." Why is it that if the
current is alternating through the house, that the black wire is
considered the hot wire? It seems to me that if the same wire is always
hot (when the current is flowing), the current is acting as direct
current. If the current is alternating within the house, why wouldn't
the black wire be hot on one cycle and the white wire by hot on the
next/return cycle?

Thanks!

The current alternates along the circuit. The black and white wires
are merely two segments of the same circuit; in other words, it's all
one big wire or loop.

Thanks! I think I understand that part... but would it have the same
effect to put, for example, an on and off switch on the white wire
instead of the black wire? I have been told that putting the switch on
the black wire cuts off the current off before it reaches the light
fixture, while putting it on the white wire allows the fixture to
remain hot (if one were foolish enough to touch the light fixture
socket).

Patrick ) wrote:
: I have always been puzzled by the fact that even though Alternating
: Current is delivered to a house, we consider one wire, usually the
: black wire, "hot" and white wire "neutral." Why is it that if the
: current is alternating through the house, that the black wire is
: considered the hot wire? It seems to me that if the same wire is always
: hot (when the current is flowing), the current is acting as direct
: current. If the current is alternating within the house, why wouldn't
: the black wire be hot on one cycle and the white wire by hot on the
: next/return cycle?

At one point in the cycle, the hot wire has a +120V potential, and the
neutral (and ground) wires are at 0, for a voltage differential of
120V. At the opposite point in the cycle, the hot wire has a -120V
potential, and the neutral (and ground) wires are at 0, for a voltage
differential of 120V "in the opposite direction". But, if you
disconnect the hot from the neutral, it is safe to touch the neutral,
but not safe to touch the hot.

I had a ceiling light fixture in my house that was wired by the
previous owner with the switch on the neutral rather than the
hot. There was an intermittent short between the neutral and ground at
the light fixture, and sometimes the light switch would work, but
sometimes the light would stay ON no matter what position the switch
was in. I could even remove the switch entirely and cap off the
wires, and the light would stay on, because the circuit was hot to
lamp to ground, bypassing the neutral and the switch.

If the switch had been on the hot side, then the neutral/ground short
wouldn't have caused much trouble. If the short had been between hot
and ground, then the circuit breaker would have popped.

--- Chip

In article . com, wrote:
The current alternates along the circuit. The black and white wires
are merely two segments of the same circuit; in other words, it's all
one big wire or loop.


Absolutely not true. The black wire is hot. The white wire is not. There *is*
a difference.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

In article . com, "Patrick" wrote:
Thanks! I think I understand that part...

Don't thank him - he's wrong - and no, you don't understand.

but would it have the same
effect to put, for example, an on and off switch on the white wire
instead of the black wire?

The light would still go on and off in response to the switch. There is a
difference, however. See below.

I have been told that putting the switch on
the black wire cuts off the current off before it reaches the light
fixture, while putting it on the white wire allows the fixture to
remain hot (if one were foolish enough to touch the light fixture
socket).

That is correct, and that is why the switch is always installed on the hot
side of the circuit.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

In article , (Charles H. Buchholtz) wrote:
Patrick ) wrote:
: I have always been puzzled by the fact that even though Alternating
: Current is delivered to a house, we consider one wire, usually the
: black wire, "hot" and white wire "neutral." Why is it that if the
: current is alternating through the house, that the black wire is
: considered the hot wire? It seems to me that if the same wire is always
: hot (when the current is flowing), the current is acting as direct
: current. If the current is alternating within the house, why wouldn't
: the black wire be hot on one cycle and the white wire by hot on the
: next/return cycle?

At one point in the cycle, the hot wire has a +120V potential, and the
neutral (and ground) wires are at 0, for a voltage differential of
120V. At the opposite point in the cycle, the hot wire has a -120V
potential, and the neutral (and ground) wires are at 0, for a voltage
differential of 120V "in the opposite direction".

Close but no cigar.
http://science.howstuffworks.com/power2.htm

But, if you
disconnect the hot from the neutral, it is safe to touch the neutral,

Like hell it is. If there's a load anywhere on the circuit, there *is* current
flowing through the neutral, and you *can* get shocked from it.

but not safe to touch the hot.

Got that part right, anyway...


--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?

"Patrick" wrote in message
oups.com...
I have always been puzzled by the fact that even though Alternating
Current is delivered to a house, we consider one wire, usually the
black wire, "hot" and white wire "neutral." Why is it that if the
current is alternating through the house, that the black wire is
considered the hot wire? It seems to me that if the same wire is always
hot (when the current is flowing), the current is acting as direct
current. If the current is alternating within the house, why wouldn't
the black wire be hot on one cycle and the white wire by hot on the
next/return cycle?

Thanks!

Because, averaged over time (one ac cycle or continuously), the "hot" (black
or red) wire will always have a potential (voltage difference) to ground.

The "neutral" or white wire will not since it is continuously forced to
ground potential by being connected to ground at the CB panel.

TKM

On 27 Mar 2005 05:49:08 -0800, someone wrote:

The current alternates along the circuit. The black and white wires
are merely two segments of the same circuit; in other words, it's all
one big wire or loop.

Jeez Roger, that helped him NOT.


Reply to NG only - this e.mail address goes to a kill file.

On Sun, 27 Mar 2005 15:12:17 +0000 (UTC), someone wrote:

At one point in the cycle, the hot wire has a +120V potential, and the
neutral (and ground) wires are at 0, for a voltage differential of
120V. At the opposite point in the cycle, the hot wire has a -120V
potential, and the neutral (and ground) wires are at 0, for a voltage
differential of 120V "in the opposite direction".

Not exactly how it works, but not far off. Actually technically true
just like a stopped clock is right twice a day, at some point the
cycle will pass thru 1v and 120v but the max potential is more than
120 and the generally accepted method of averaging or figuring the net
effect (I believe that's root mean squared???) "averages" out to 120.


Reply to NG only - this e.mail address goes to a kill file.

On 27 Mar 2005 05:09:09 -0800, someone wrote:

It seems to me that if the same wire is always
hot (when the current is flowing), the current is acting as direct
current.

Nah. The black (or red!) wire has a sine wave current in it that
alternates back and forth, you might think of it as from plus to
minus. Whereas the white wire is supposed to be at ground potential.
If everything is perfect, in practice you would USUALLY be ok touching
the white - the "stick you finger in the socket" situation, you can
indeed USUALLY get away with it when the black has been switched off.

You get 120/240 because the red and white are at opposite phases, its
240 between them and 120 from each to white neutral.

In theory and code you don't allow anyone to touch the white as their
are possible faults where a potential could develope that would cause
current to flow.


Reply to NG only - this e.mail address goes to a kill file.

Thanks to all that replied.

If I understand the last reply correctly, the alternating current is
alternating back and forth through the black/red wire. The source of
the current comes from the panel through the black wire, never through
the white wire.

What is the purpose of the white wire? To complete the loop? Where is
the loop completed? At the panel?

In article .com, "Patrick" wrote:
Thanks to all that replied.

If I understand the last reply correctly, the alternating current is
alternating back and forth through the black/red wire. The source of
the current comes from the panel through the black wire, never through
the white wire.

That is correct (provided that the connections in the panel are made
correctly).

What is the purpose of the white wire? To complete the loop?

Correct. An analogy with plumbing may be useful: the black wire is the supply
pipe, and the white wire is the drain.

Where is the loop completed? At the panel?

Correct.

--
Regards,
Doug Miller (alphageek at milmac dot com)

Nobody ever left footprints in the sands of time by sitting on his butt.
And who wants to leave buttprints in the sands of time?