# Confusion on AC in LIVE & NEUTRAL WIRE

So if an AC current means the elctrons are alternating or changing direction in a given time, how does this apply to live & neutral wire, don't they flow in one direction only? Please answer it as simple as possible, I'm only a high school kid.

• Wires allow current flow in both directions. – Jon Custer Oct 15 '18 at 14:41
• There is an AC voltage between the live wire and ground while there should not be a significant AC voltage between the neutral wire and ground. I'm not clear on why this might be interpreted to mean the electrons flow in one direction only in these wires. Would you please edit your question to explain your reasoning? Also, see this related Q & A here: Difference between live and neutral wires – Hal Hollis Oct 15 '18 at 15:09
• The answer that Hal Hollis linked is pretty long. The short version is, the entire power grid is connected to Earth at regular intervals because otherwise, atmospheric electricity could charge the overhead wires to dangerously high voltage with respect to Earth. The "neutral" wire is whichever one is connected to Earth. All of the other wires are "Live." If you are connected to Earth, and you touch the neutral, you won't get hurt, but if you touch a "live" wire, then it will hurt. – Solomon Slow Oct 15 '18 at 15:27
• Crossposted to electronics.stackexchange.com/q/401559/52589 – Qmechanic Oct 17 '18 at 17:29
• @SolomonSlow but the hot wire is connected to the neutral wire in a circuit. The current flows in a closed circuit. And that's even before we consider real flow vs conventional. Totally confused. In an ac circuit isn't current alternating? Why should the hot wire be any more dangerous than the neutral? I'm caught up on definitions here. Please help 😂 – HörmannHH Sep 19 at 5:29

This is a follow-up to a comment I left at the OP's closed question here

how does this apply to live & neutral wire, don't they flow in one direction only

Here's an image of 240VAC versus 240VDC

Stipulate that the live wire has 240VAC relative to the neutral (return) wire and that the neutral wire is held at 0V.

This means that the live wire is alternately more positive and then more negative with respect to the neutral wire.

Assuming a resistive load (imagine a light bulb connected between live and neutral), the mobile electrons in the bulb filament move away from the neutral towards the live wire when the live wire voltage is positive and move from the live wire towards the neutral when the live wire is negative.

Thus, the current through the bulb (and wires) alternates in direction as the live voltage alternates in polarity. That is, the current is an alternating current (AC) and not a DC (unidirectional) current.

• But how does the neutral wire is 0V all the time, doesn't it alternates everytime? – user209491 Oct 17 '18 at 13:39
• @PCMining, what is the it that you think should be alternating? Note carefully that I specified in the very first sentence that the live wire has 240VAC relative to the neutral wire. Thus, the voltage across the live and neutral wires is alternating. If a resistor is placed across the live and neutral wires, the voltage across the resistor is alternating and thus, the current through the resistor is alternating. It's completely irrelevant to this result if the neutral wire is at 0V with respect to ground. – Alfred Centauri Oct 17 '18 at 14:37
• But the wire isn't. You are applying 240v ac to the wire. That's the ops, and mine, issue. There is a negative voltage at the neutral wire during half a full ac cycle .. Alternating current. – HörmannHH Sep 19 at 5:33
• @HörmannHH, it simply isn't the case that "There is a negative voltage at the neutral wire during half a full ac cycle". Please take a look at this Wikipedia article Split-phase electric power and see that the neutral wire is grounded, i.e., the voltage on the neutral wire is (ideally) the same as the ground, the 0V reference voltage. The live wire(s) are alternately positive and negative with respect to the 0V neutral wire. – Alfred Centauri Sep 19 at 12:06

As you have noted, there is a live and a neutral wire leaving the circuit breaker panel (*note 1) to your load. Because this is alternating current, during half of the cycle the circuit in the live wire is flowing out of the panel, and during the other half it flows in to the panel.

Now, the key here is that during the time that current flows out the live wire, it flows back in the neutral wire. The neutral wire completes the circuit, giving a return path for the current. Similarly, when the current flows in the live wire, it flows out the neutral. At any given time, whatever current flows through the live wire, an equal amount (*note 2) flows in the opposite direction through the neutral wire. It's a great example of Kirchoff's current rule!

(*note 1) Older panels use fuses instead of circuit breakers. In either case, at the panel the neutral is connected to Earth ground. But none of this matters for explaining your question.

(*note 2) When things are working correctly, the currents should be equal and opposite. Occasionally, the current finds another path back -- often through a human being, causing an electric shock. We call this a "ground fault". There are devices called "ground fault circuit interrupters" that measure the difference between the live and neutral currents; if the difference in current is large enough, they shut off the circuit. You can often see these devices in bathrooms and kitchens, with buttons labelled "TEST" and "RESET". Now you know what those are for!

My understanding is that the electrons are alternating between 2 hot wires which has a voltage of 240V. Imaging those two hot wires like left and right jabs from a boxer, and the neutral wire is neither the left or the right jab, but a third arm in the middle not jabbing at all....So the electrons come from left arm, then come from the right arm like alternating jabs, and all return through the middle arm. The voltage between the middle arm and the left or right arm is 120V. Since there is no electron coming from the middle arm (no jab), you won't get a electric shock, or punched:)