Does the direction of current inverse in ac?

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Discussion Overview

The discussion revolves around the behavior of alternating current (AC), specifically addressing the direction of current flow, the roles of live and neutral wires, and the implications of polarity inversion in AC systems. Participants explore theoretical concepts, practical implications, and common confusions regarding AC electricity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that while AC is characterized by alternating polarity, there is confusion about whether current flows from live to neutral or vice versa, especially during polarity inversion.
  • Another participant clarifies that alternating current can have a DC offset, but in standard mains voltage, the current does indeed alternate direction.
  • A different participant asserts that both voltage and current reverse direction at the line frequency, questioning the meaning of "only the phase inverses."
  • One participant compares electricity flow to heat or water, suggesting it always flows from high to low potential, raising questions about the role of neutral in this context.
  • Some participants discuss the nature of the neutral wire, indicating it can carry current and is tied to ground, which contributes to its designation as "neutral."
  • There is a suggestion that when the polarity inverts, the current direction changes from neutral to live, prompting questions about how this is possible.
  • Another participant emphasizes that current requires a return path to complete a circuit, which is provided by the neutral wire, and notes that the labeling of wires is somewhat arbitrary in terms of electron flow.

Areas of Agreement / Disagreement

Participants express differing views on the nature of current flow in AC systems, particularly regarding the roles of live and neutral wires and the implications of polarity inversion. There is no consensus on these points, and the discussion remains unresolved.

Contextual Notes

Some statements reflect assumptions about the definitions of live and neutral, as well as the conditions under which current flows. The discussion does not resolve these assumptions or clarify the implications of different wiring configurations.

ChrisToffer
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I'm learning AC and theory says that the polarity of AC inverses.. even the name says 'alternating current'.. now what about the live and neutral? does the current goes from neutral to live and and vice versa?
Some people says that only the phase inverses, but the current is always from live to neutral, and direction of current never inverses..
Is all these true?? can someone help me understand all these?? and why do transformers has only one color for both wires? like, transmission transformers also are pretty much same, i mean same principle.. I'm so confused..
 
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Alternating current doesn't necessarily mean it is centered at 0. You could have an alternating signal with a DC offset so that it always stays positive.

However I think you are talking about regular mains voltage centered on zero. And yes, it does alternate going forward to going backward. It is rather easy to think about. If you had a battery run circuit and switch the terminals every second, the current would going 'backwards' every other second right?
 
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Yes, the voltage AND the current reverses at line frequency (60Hz in US). I have no idea what the phrase "only the phase inverses" means to "some people". Phase relative to what?

Additionally, the relative phase of the voltage and current can be non-zero, giving rise to "power factor". That is, you don't always get maximum current at maximum voltage. Wikipedia is a fine place to read about power factor.
 
also, something that obvious that helped me when I was first learning...

Electricity is like heat or water. It will always flow from High to Low. If at some point in time, neutral is 0V and the line is -5V, then the neutral is High and it has to flow from neutral to the line.
 
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if the direction has reversed, it means that the live became neutral?
 
ChrisToffer said:
if the direction has reversed, it means that the live became neutral?

The neutral wire is always a live wire (a current carrying conductor). It's said to be neutral because it's normally attached to ground at some point in a grounded power system and/or is a reference point for other wires IRT voltage.
 
Last edited:
Neutral is called such due to the way it is attached to the transformer or group of transformers.
 
i know that the polarity will inverse periodically, phase and current directions would change.. yes but the live is the hot wire, current will flow to neutral.. but when the polarity inverses, the direction of current has changed, that is from neutral to live.. but how is it possible that current now goes from neutral to live??
 
if you touch the 'live' wire and nothing else, will you get zapped? no.
if you touch the 'live' wire and the 'neutral' wire, will you get zapped? yes.

How can the 'live' wire be live if you touch it and nothing happens? Because current needs a return path.

the neutral wire carries the return current. Current has to return in order to form a circuit. But the direction we say its going in is fairly arbitrary as long we stay consistent with our notation. The electrons don't care what the wire is labeled. They flow through them regardless. If voltage is applied one way, they go that way. If voltage is reversed, the electrons turn around.

Its called neutral because it is tied to ground. If you touch the ground and the neutral wire, nothing happens because there is no voltage difference. But it still carries current when it is connected to a circuit.
 

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