I read some articles and watched videos regarding 1 phase and 3 phase AC. I later found out that for most home appliances we need 1 phase AC.

Then I came to know about live and neutral wires. Few articles said neutral wire (blue) has 0 potential. And live wire (red) has high potential. Neutral wire is to return the current back to source.

(I also read about earth wire. That was the thing that lead me to this question but I'll ask about that later)

All these things gave me 3 doubts for now.

  1. If neutral wire returns the current, the same which was in live/red wire, why doesn't it give shock?

  2. Would it make any difference if you connect the bulb using 2 different methods as shown in image? (I have assumed a blub is connected this way. There are two points, one for in and one for out)

  3. If current keeps changing its direction many times a second, that means current should keep flowing from red to blue, blue to red and continuously. How is it even possible to flow current from blue/neutral wire? Where would current come in blue wire? From Earth?

Okay these might seem too broad, but I believe these are very much related but I have separate doubts since I don't understand the concept fully.

enter image description here

PS: Simple and not very scientific language would be appreciated :)

  • 1
    \$\begingroup\$ I have reopened this question as, while it is similar to this one it is a genuine attempt to obtain understanding and of especial value to the OP. \$\endgroup\$
    – Russell McMahon
    Commented Jun 17, 2021 at 1:40

1 Answer 1

  1. The neutral wire is tied to a potential of 0V in comparison to ground with a very low resistance. This means, that high currents can flow through the neutral wire without any noticable voltage appearing on the neutral wire (Ohms law: U = R*I). Without any voltage on the neutral wire you can not get shocked (the high current can only flow through the neutral wire because of its low resistance. Your body has a pretty high resistance and needs some significant voltage to get a current flowing).

  2. Your first picture is the correct way to connect the light bulb. The live wire supplies the high voltage (110V or 230V) and current, the neutral wire is sinking the current. In your second picture both terminals of the light bulb are connected to the same potential - both to the live voltage. Without a potential difference between the terminals, there will be no flow of current through the light bulb (again: U = R*I or I = U/R). At the same time you are connecting the live wire with neutral wire without a load in between - this will create a short circuit and a very high current. Hopefully the circuit breaker would trigger in this case ;)

  3. As I wrote above, the neutral wire has a potential of 0V and sinks the current back to the generator (or actually to the next transformer). It does not mattter whether the live voltage is positive oder negative. You are right, the polarity is changing rapidly with either 50Hz or 60Hz (depending on where you live). The only thing that changes is the direction of the current flow. In the case of a positive live voltage you have a positive current and in the case of a negative live voltage you have a negative current (minus sign just means, that the current flows in the other direction).

Edit: See the picture below. The neutral wire is on 0V, which is represented by the black horizontal line in the middle. The live voltage follows the curve of a sine wave and is alternatingly positive and negative. When on positive potential, the potential is higher than neutral, but when the potential is negative, it is actually lower than 0V. The current is always flowing from the high potential to the negative one, so when the polarity of the live wire switches, so does the direction of current flow.

enter image description here
Image from learn.sparkfun.com

  • \$\begingroup\$ The neutral wire is tied to a potential of 0V in comparison to ground with a very low resistance. I didn't get this. You mean potential of point where blue wire is attached to bulb has 0V? And other end which is inside earth/ground also has 0V because Earth has 0 potential? And if both ends have 0V, why would current flow? \$\endgroup\$
    – Vikas
    Commented Sep 13, 2019 at 8:02
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    \$\begingroup\$ OK, you got me there. There actually is a voltage on neutral when a current is flowing - but it is really very very small in comparison to the live wire and we can assume it to be about 0V. But you are right, U=R*I tells us, that even with a very small resistance there has to be at least some voltage. \$\endgroup\$
    – jusaca
    Commented Sep 13, 2019 at 8:06
  • \$\begingroup\$ Oh. Now I think I understand one more thing. The current in live wire flows only when it is connected to a resistance like bulb? Or when you touch it! Because current flows from high to low voltage? Am I right? \$\endgroup\$
    – Vikas
    Commented Sep 13, 2019 at 8:20
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    \$\begingroup\$ Exactly! As long as the live wire is dangling around in free air you have a voltage - but no current! The current starts flowing the moment you "close the circuit" with some load, either a bulb, you or a short circuit ;) \$\endgroup\$
    – jusaca
    Commented Sep 13, 2019 at 8:26
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    \$\begingroup\$ I added a picture and some text to my answer, I hope that makes it more clear. \$\endgroup\$
    – jusaca
    Commented Sep 13, 2019 at 8:44

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