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Neutral Wire

  1. Mar 13, 2008 #1
    Why the neutral wire (the cold) does not cause an electric shock?
     
  2. jcsd
  3. Mar 13, 2008 #2

    stewartcs

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  4. Mar 13, 2008 #3
    In a properly balanced power distribution system the neutral should have no current flowing through it, also it is often grounded.
     
  5. Mar 14, 2008 #4

    chroot

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    This is incorrect; the neutral conductor provides the return path for the current from the hot conductor. In a properly-built electrical system, the neutral conductor is at the same potential as earth ground, though, meaning that you cannot receive a shock between it and ground.

    - Warren
     
  6. Mar 14, 2008 #5
    Technically we are both correct....in 'real' electrical power systems a neutral wire carries only the unbalanced current from a Y-connected system due to unbalanced loads. It is not necessarily earthed, however owing to it's nature and how it is sometimes connected to earth you are right in saying there is no potential between it and ground.

    You are talking of the other use of the word neutral where it is the cable that links back to the grid. NB - if you can be shocked by the neutral if you provide a quicker path to ground when the neutral has current flowing through it.
     
  7. Mar 14, 2008 #6

    Danger

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    I assume from your use of the word 'earthed' that you're British. Here, there isn't more than one use of the word 'neutral'. Black is hot, white is system neutral, and green is ground (earth). That's for regular domestic stuff, though. Fancier industrial systems such as 3-phase might have different terms that I'm unaware of.
     
  8. Mar 15, 2008 #7

    russ_watters

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    Nope.
     
  9. Mar 15, 2008 #8

    Danger

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    'Nope' as in I'm wrong, or 'nope' as in the terms are the same? :confused:
     
  10. Mar 15, 2008 #9

    russ_watters

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    Fancier industrial systems use the same type of terms and color schemes.
     
  11. Mar 15, 2008 #10
    However neutral in the home and neutral in three phase isn't actually the same thing...not quite.
     
  12. Mar 15, 2008 #11

    Danger

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    Can you elaborate upon that, Mike?
     
  13. Mar 15, 2008 #12
    Sure, I assume that you know what three phase power is...if not have a read of this article I wrote for the UKSLC....(there is an error in how the 415V (for UK mains) is reached but other than that it's all fine)

    http://www.ukslc.org/articles/power/3_phase_power_explanation.html

    Now, in a perfectly balanced three phase system (where each of the phases is loaded with an equal impedance you can connect the ends together as shown in this diagram (from the above article)

    http://www.ukslc.org/images/articles/threephase/fig40001.gif

    Unfortunately it's hard to balance the load perfectly in a large transmission system, so a neutral wire is connected between where the three loads and three generators meet taking the excess current. This is the neutral in the three phase system. The neutral in your house just goes from you, the load, to the point where all of the loads connect.... while your neutral is connected to the neutral that I have explained it doesn't necessarily have to be.

    I suppose what I'm saying is that the current in the neutral line in your house does not necessarily flow down the neutral of the larger three phase system, so it is different while being connected.
     
  14. Mar 16, 2008 #13
    Ah ha! My speciality!!

    I have been doing electrical work for a while, and I might have an answer.

    First, Have you ever grabbed a neutral? I've gotten hit with one, and took a meter to it and it had 70v pumping through it. But that was probably someone's screw up.
    ANYWAY

    there is a difference between it and the ground.

    The ground is a safety device. Almost all every day devices can operate without it, but NEC demands it in most cases. The neutral is essential for current to travel, for it provides resistance for the current to push against. There shouldn't be any current going through it, but mistakes happen.
     
  15. Mar 16, 2008 #14
    depending of the voltage, the phases have different color codes. you have different combos for 120, 240, 277, and 480 (in USA at least)
     
  16. Mar 16, 2008 #15
    well the way i see it the neutral wire is the centre tap of the transformer. not a ground but ussually connectected to ground at a certain point at the electrical box. so say if we have an transformer with three wires and one is the center tap. now until any part of the circuit is referenced to ground there is no circuit and no current path. if somehow the wrong part of the circuit is referenced to ground the neutral wire will have a voltage potential to ground. hope this helps
     
  17. Mar 16, 2008 #16
    In the UK you only really have combinations for 230/240V and 415V (That's the phase and line voltages)
     
  18. Mar 22, 2008 #17
    let me put it this way. unless you have a circuit loop you can not have a current flow. so regardless of where or what voltages you have. the high voltage is reduced to the operational voltages by transformers. these transformers are referenced or grounded to earth at a certain point ussually with the centertap of the transformer at a certain point. then you have say 120 v per line wrt the center tap or neutral wire. phase or 240 v across l1 l2. now if you have a long run of wire you will have a resistance and a voltage drop accross the wire and you may get a shock if you touch the wire and ground at the same time. as for the wire color in the UK may be different but the principles of the circuit will remain constant. as for 3 phase same thing just your phases wrt neutral
     
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