How can polarity of AC inverse but keep the live hot and neutral cold?

In summary, the polarity in an AC circuit inverses, causing a change in the flow of current. The neutral wire is typically connected to ground, resulting in no potential difference between the two. This means that the neutral wire remains at a constant potential and is always considered "cold," while the "hot" wire can have a potential difference and is the one that can deliver a shock. It is important to always consider voltage as a potential difference between two points and to be aware of the grounding of the neutral wire in an AC circuit. In rare cases where the neutral is not grounded, it must be treated as a "hot" wire for safety purposes.
  • #1
ChrisToffer
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In an AC circuit, we know that the polarity inverses, and what i know is that the flow of current also will therefore inverse.. which means that the live will become negative and the neutral will become positive.. What i can't understand is how the polarity inverses but the live is still the hot wire and the neutral stays the cold one? i mean the polarity of each should have been reversed..
I need a very good explanation of it, I've asked many people the same question but any clear answer.. someone here may help me understand this?
 
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  • #2
The answer to your question is simple. Cold wire is connected to ground (earth). So there is now potential difference between cold wire and ground. And this is why cold wire always stay cold.

As a remainder

To measure the voltage we need two point in the space. One of this point is treat as a reference point. We have a very similarity situation when we try to measure a height of an object. We need a reference point. The most common reference pint is "above mean sea level". But when you measure the height of the table in your house the floor now becomes your reference point.

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  • #3
It may be best to refer to a diagram - The Neutral is typically connected to Ground - so when we measure the Neutral - relative to the ground - we see no voltage ( under normal / ideal conditions).
Note the normal load current still flows in the ground, and this current changes direction with the AC Cycle.

There are rare cases where the neutral is not grounded, in that case it will have a voltage ( relative to ground) and must be treated the same as a "hot" ( Also note - from a safety standpoint- the neutral should always be treated as a "hot" lead - e.g. calling it "cold" is not correct)
 
  • #4
Jony and Windadct both hit it.
But there's an easier way to remember. Awareness of it will keep you out of trouble later in your studies.
It goes back to the definition of voltage, which we tend to forget.

Voltage is a potential difference.

Your "Cold" wire is earthed, so it can't develop(or sustain) a potential difference between itself and earth.

Your "Hot" wire can develop (or have applied to it) potential difference between itself and earth,, and of either polarity.

So when you speak of voltage, always ask yourself "Between where and where else?"

That's why voltmeters have two leads.
 
  • #5
jim hardy said:
Jony and Windadct both hit it.
But there's an easier way to remember. Awareness of it will keep you out of trouble later in your studies.
It goes back to the definition of voltage, which we tend to forget.

Voltage is a potential difference.

Your "Cold" wire is earthed, so it can't develop(or sustain) a potential difference between itself and earth.

Your "Hot" wire can develop (or have applied to it) potential difference between itself and earth,, and of either polarity.

So when you speak of voltage, always ask yourself "Between where and where else?"

That's why voltmeters have two leads.

That says it all. The fact that one of the conductors is 'chosen' to be held at near Earth potential has nothing to do with what's going on 'between' the two conductors. If you were bouncing up and down on a bungee cord, you wouldn't be aware of whether you jumped off a high bridge or had been let go from a hook on the ground.
Some electrical supplies use two 'floating' conductors (the outputs from an isolating transformer). The advantage is that, if you happen to get connected to either conductor, then it quickly comes to your (Earth) potential and you do not get a shock. Floating systems are only suitable in certain situations, where just one piece of equipment is being fed.
 
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1. How does the polarity of AC affect electrical circuits?

The polarity of AC refers to the direction of the current flow. In electrical circuits, the direction of the current flow determines the direction of the magnetic field and the direction of the force exerted on charged particles. This can affect the performance and functionality of electronic devices.

2. Can the polarity of AC be reversed?

Yes, the polarity of AC can be reversed by switching the connections of the live and neutral wires. This is often done to test the functionality of a circuit or to troubleshoot any issues with the direction of current flow.

3. How can the polarity of AC be inverted while keeping the live wire hot and the neutral wire cold?

This can be achieved by using a special type of transformer called an isolation transformer. This transformer isolates the live and neutral wires, allowing for the reversal of polarity without affecting the temperature of the wires.

4. Why is it important to maintain proper polarity in electrical circuits?

Maintaining proper polarity in electrical circuits ensures that electronic devices operate correctly and safely. Incorrect polarity can lead to malfunctioning devices, electrical shocks, or even fires.

5. What are some common methods for testing the polarity of AC?

Some common methods for testing the polarity of AC include using a multimeter, a polarity tester, or an isolation transformer. These tools can help determine the direction of current flow and identify any polarity issues in the circuit.

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