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How can a wire be called the "hot" wire and another the "neutral" wire when ac current reverses itself 60x/sec? For first half of a given cycle it flows from the "hot" wire to the load and back out to the source through the "neutral" wire. Since ac reverses itself in the second half of the cycle, it flows from the "neutral" to the load and back to the source through the "hot" wire. So they are alternately the "hot" and "neutral" wire depending on which half of the cycle we are in?

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marked as duplicate by Alfred Centauri, Buzz, John Rennie, Jon Custer, stafusa Jan 13 at 21:38

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  • $\begingroup$ Not so much physics as how the electrical network is wired: one side is grounded, the other side alternatingly positive and negative with respect to ground. $\endgroup$ – Pieter Jan 12 at 22:35
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The terms hot and neutral are nothing to do with current rather they are to do with potential difference (voltage).

A 220 V rms ac supply means that the potential difference between the hot wire and the neutral wire varies between $+\sqrt 2 \times 220 \rm V$ and $-\sqrt 2 \times 220 \rm V$.

The neutral wire is connected to the ground and so the potential difference between the neutral and the ground is (approximately) zero.
If you are standing on the ground and touch the neutral wire there is no potential difference across you and so you do not get an electrical shock.

However if you are standing on the ground and touch the hot (live) wire the potential difference across you varies between $+\sqrt 2 \times 220 \rm V$ and $-\sqrt 2 \times 220 \rm V$.
As a result you would get an electrical shock which may be fatal.

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  • $\begingroup$ one minute of each other. Nice! $\endgroup$ – Bob D Jan 12 at 23:12
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The idea of “hot” versus “neutral” relates to the sensation you would have when touching the wire. That is, the sensation of "electric shock".

The electrical system in your home has one side earth grounded. The neutral wires in the circuits of your home are connected to this earth ground. Therefore the neutral wires are approximately at the same electrical potential as earth ground. If you touch the neutral with one part of your body (say one hand) and another part of your body (say your other hand) with something connected to earth ground, you will sense little or nothing because the voltage between them is very low. But if you touch a wire that is at a voltage of 120 volts to ground (the so called “hot” wire) with one hand, and the other hand contact earth ground (or something connected to earth ground) you will say “ouch”. It’s not exactly the same reaction as touching something that is thermally “hot”, but I think you can get the idea.

Hope this helps.

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