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Homework Help: Electron flow in live and neutral wires

  1. Oct 1, 2013 #1
    Our Physics teacher used to tell us that in an ac circuit the current and hence the flow of electrons is reversed every half cycle as the polarity of the supply changes every half cycle. However I am still puzzled about the following. In the UK, the live is the wire that delivers electrical power from the power grid while the neutral is the return wire.

    If this is so does it mean that the flow of electrons is reversed in BOTH live and neutral wires every half cycle?

    Why does the direction of the current change if the live remains live while the neutral remains neutral all the time? Is there a good analogy to explain this concept better?

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  2. jcsd
  3. Oct 1, 2013 #2

    Simon Bridge

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    "Neutral" and "phase" are names for the roles - the phase is used for the reference voltage.
    Power is transmitted to your house as a travelling wave. It comes in the phase and out the neutral. Current goes back and forth in both.

    iirc. many countries ground the neutral wire - which is why the phase is considered "live".
    But the neutral side of the light bulb must still carry power - while the bulb is lit - proved by adding another bulb in series. This is similar to the negative lead in DC circuits. You can get a shock off neutral is your body provides a better ground than the fusebox.

    There's lots of info online about how homes are wired and why.
  4. Oct 1, 2013 #3


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    In principle, the neutral is at roughly Earth voltage, yet electrons do indeed alternate in direction along it just as they do along the line (or live). In a three phase suburban supply, all houses get the same neutral connection but different phases of the live. So if three successive houses are taking the same current from their three different phases, the oscillations on the neutral cancel out. However the neutral should not be considered as safe as ground because a high current drawn by a single house (maybe during a short) could produce a significant voltage on nearby sections of the neutral.
    The US 2 phase domestic supply works on the same principle.
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