A residential 120V AC/60 Hz parallel circuit with one hot wire (usually black) and one "neutral" grounded conductor (usually white) has one "hot side" and one grounded side through which the current returns. (note: many of these residential circuits have green grounding wires, which are not related to the white grounded conductor. The green ground wires are not relevant to the question.) The question: If the AC source is alternating current direction and switching voltage polarity with every cycle, why don't the hot side and the neutral side reverse in the circuit along with the cycle? The hot side should become neutral, and the neutal side should become hot.

 

Originally posted by Energizer@Apr 15 2005, 07:46 PM
A residential 120V AC/60 Hz parallel circuit with one hot wire (usually black) and one "neutral" grounded conductor (usually white) has one "hot side" and one grounded side through which the current returns. (note: many of these residential circuits have green grounding wires, which are not related to the white grounded conductor. The green ground wires are not relevant to the question.) The question: If the AC source is alternating current direction and switching voltage polarity with every cycle, why don't the hot side and the neutral side reverse in the circuit along with the cycle? The hot side should become neutral, and the neutal side should become hot.

[post=6972]Quoted post[/post]​

The so-called "hot" wire is called that because it is the one you have to be careful with. (It is that one which has the large voltage difference to earth - the neutral being connected to earth at the source.)

Imagine a battery with a voltage high enough to be dangerous - pick any number you like.

Suppose we connect one terminal of it to earth. The polarity is totally irrelevant.

If you touch the other terminal you will get a shock.

Now reverse the polrity of the battery, connecting the other terminal to earth instead.

If you touch the terminal which is not connected to earth you will get a shock.

The teminal not connected to earth, whatever the polarity is still "hot" with respect to earth.

Much the same with the a.c. mains. The polarity of the "hot" wire changes 50 or 60 times a second.