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When a power source is AC (alternating current) one is a phase and the other is neutral.

Does phase and neutral lines change their polarity over time or only phase line voltage and current up and down sinusoidal form? Which one is correct? If it is not changing the polarity, how do rectifiers work?

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  • \$\begingroup\$ What do you mean, precisely, with "polarity"? (the answer is really in understanding what a voltage and a polarity is) \$\endgroup\$ Jul 24 at 13:32
  • \$\begingroup\$ for me, polarity means the current flow direction. \$\endgroup\$ Jul 24 at 13:37
  • \$\begingroup\$ where exactly does the current flow! Be very exact in everything you say. \$\endgroup\$ Jul 24 at 13:49
  • \$\begingroup\$ at the closed circuit with different potentials in the direction of high to low. \$\endgroup\$ Jul 24 at 14:05
  • \$\begingroup\$ exactly, so the closed circuit comprises both the phase and the neutral, right. The direction of current in these two are always opposite, by principle, at every point in time, no matter whether DC or AC. \$\endgroup\$ Jul 24 at 14:06
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When a power source is AC (Alternative Current) one is a phase and the other is neutral.

AC stands for alternating current, not "alternative" current.

The neutral is so-called because it has been neutralised by connecting it to earth / ground.

schematic

simulate this circuit – Schematic created using CircuitLab

Figure 1. Two AC supplies. (a) has no ground reference and so neither line has been neutralised and neither can be called "neutral". (b) has one secondary connection connected to earth and so that conductor is neutral and the other is live.

Does phase and neutral lines are changing their polarity over time or on phase line voltage and current up and down sinusoidal form?

Your sentence is rather confused. Neutral has very little voltage on it and can be considered to be at 0 V for basic analysis. The live wire voltage oscillates in a sinusoidal wave from peak positive voltage to peak negative voltage.

If it is not changing the polarity of how rectifiers work.

You can't "change the polarity of how rectifiers work". You can, however, edit your question to clarify. If you do that we can try and help you further.

schematic

simulate this circuit

Figure 2. (a) The full bridge rectifier. (b) When the AC is positive (as defined by the secondary dot) D5 and D8 conduct. (c) When the AC is negative D11 and D10 conduct.

No matter which polarity the AC is the diodes steer the current to the positive output.

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  • \$\begingroup\$ Thank you a lot sir/madam. you can clear my dought here from your answer. how negativity and positivity are created at the single wire while the neutral side is zero voltage \$\endgroup\$ Jul 24 at 21:37
  • \$\begingroup\$ That's the definition of AC. The voltage alternates sign and the current alternates direction. See youtube.com/watch?v=gQyamjPrw-U&ab_channel=creativeLearning. \$\endgroup\$
    – Transistor
    Jul 24 at 21:39
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A load may be single Line or dual for twice the voltage with Neutral bonded to Earth ground at the transformer,

Thus the voltage is supplied by the “Line” side which requires a breaker and Neutral supplies the return path for alternating current limited by up to 5% rise above ground by design of cables at max rated distribution current. ( or as defined by local specs)

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Phase line brings current to the load. And the current comes out of the load. The current needs the neutral line to complete the circuit. Finally the load will run. AC is different from DC because AC has frequency like 50Hz or 60Hz. So every second, it goes forward and reverse direction for 50 or 60 times. You can see it in a sine wave. In rectifier, it only considers forward direction only.

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