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Basic electricity

  1. Oct 19, 2015 #1
    What is the neutral wire? Why do we need that?
     
  2. jcsd
  3. Oct 19, 2015 #2
    Neutral wire provide a path for a returning current to the "source" (neutral is a wire that carrying the full load current).
     
  4. Oct 19, 2015 #3
    Thank you for your response.
    Some you tube videos say alternating current changes directions frequently. Does it change back and fourth through the two hot wires? why doesn't the neutral cause a short? Other sources say high-tension lines can overbuild up too much charge causing risk of "static" discharge; would this be a short? or Ground?
     
    Last edited: Oct 19, 2015
  5. Oct 19, 2015 #4
    Hello Russel and Welcome - I disagree a little with Jony, the Neutral wire does provide a path back to the source, but does not necessarily carry the full load current. Think of the the Neutral as a Neutral point in the system. In most (not all) systems the neutral is grounded near the source. This allows for a path of current back to the source, but keeps the ground out of the normal path - there are many reasons for this being beneficial.

    And yes - Alternating Current "alternates" direction but this is both current and voltage - So power can be delivered TO the load with the current flowing in both directions - this is represented in P = V * I .

    So a load can be load can be connected between a "hot" leg and the neutral - the current then flows through the load and the neutral. But you would not connect the Neutral to the Hot leg - this would cause a short - the idea is to deliver energy to a load.
     
  6. Oct 19, 2015 #5
    As for the AC current we simply measure all the voltage with respect to the neutral wire (neutral wire is our reference point).
    View attachment 85300
    And this means that
    And we in Europe use this grid system.
     
  7. Oct 19, 2015 #6
    So if the Neutral is grounded near the source, won't that break the circuit? In other words; if the load comes from the hot leg to the resistance (application) then to the Neutral (ground) why do we call it the Neutral not Ground? And why can't we ground it at the resistance like DC?
     
  8. Oct 19, 2015 #7
    So let's see if I have this straight. The application doesn't care if the load is positive or negative, as long as there is current carrying voltage back and fourth; or in one direction for that matter, as long as there is current.
     
  9. Oct 19, 2015 #8

    davenn

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    Greetings Russell
    welcome to PF :smile:

    The neutral is connected to ground in several common places ...
    1) at the power station,
    2) at the transformer pole in your street/suburb,
    3) at the power distribution board in your house or business

    we call it neutral, because we ALSO have an earth (ground) wire in a standard 3 pin plug/socket .... Some appliances only have a hot (phase/live) and neutral.
    Others have an earth ( ground) wire as well that connects to the appliances metal chassis/casing

    have no idea what you mean by that ... a DC circuit also uses 2 wires the positive wire and negative aka 0V wire

    a lot of confusion in there
    voltage isn't carried anywhere. Moving electrons are the current. The electrons are the charge carriers
    many AC appliances don't care about polarity .... a light globe, a heater ( in all its forms ... oven (not microwave), room heater, jug/kettle)
    Other things require the correct phase and neutral connections ... eg motors

    In an AC system, the electrons don't really go anywhere, they just move rapidly back and forward about a point/position ( oscillate)
    Your light globe in your house will never see the electrons that are moving in the wire in the generator at the power station

    It is the EM (electromagnetic) wave that carries the energy through the circuit


    Dave
     
  10. Oct 19, 2015 #9
     
  11. Oct 19, 2015 #10

    davenn

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    because you DONT want the metal chassis to be part of the AC circuit

    the separate earth connection gives a safety factor, if the phase/live becomes dislodged and touches the chassis, there will be an instant fuse blow back at the power panel



    D
     
  12. Oct 19, 2015 #11
    My question is; what is the difference between in neutral in the ground? Especially if you're going to connect the neutral to the ground after it's done whatever job it has to do? And how can it do that job if it gets connected to ground before it reaches the transformer?
     
  13. Oct 19, 2015 #12
    So the grounded conductor is a phase of the circuit ? And the ground is a safety from fault?
     
  14. Oct 20, 2015 #13
    The ground provides path for fault current. This happened at a site where i worked. My laptop would give me electric shocks. There was no ground at the socket where I would plug the charger. If i'd touch the metallic edge of the laptop I'd get small currents. I made a practice of using a page to flip open the laptop n was careful to restrict touching only the keyboard.

    if there is any insulation failure in the appliance n if you touch the metallic edge, then leakage current may flow from appliance edge to ground through your body. but if the appliance is grounded, then the leakage current will flow through the ground wire.
    a ground wire isnt supposed to carry current under normal conditions. though the secondary of transformer is grounded, current wont flow through it under normal conditions.
    electric_hookup_okay.jpg
     
  15. Oct 20, 2015 #14

    dlgoff

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    Yes. This is correct. I just wanted to post a couple of my favorite images from http://ecmweb.com/bonding-amp-grounding/grounding-vs-bonding-part-1-12

    This one shows the currents path of a fault through the safety ground.

    501ecm17fig2.jpg

    This one shows the "touch potential" due to an inadequate ground.

    501ecm17fig4.jpg
     
  16. Oct 20, 2015 #15
    Thanks for the image dlgoff. I have one question. Current always flows through least resistive path. So in the first image, if we look to the left, then at the secondary of the transformer why does current flow X1---meter---main---panel---outlet---load---X0 instead of X1---X0---ground, since X0 is grounded?
     
  17. Oct 20, 2015 #16
    J-T -- the current needs to flow in a loop. If it goes X1 - X0 - Ground- then to where? -- Be careful with the thought "Current always flows through least restive path." - this can be misleading thinking that ALL of the current flows in the least restive path; when we have 2 or more paths the current will divide and the least restive will carry more current than the higher restive path.
    Russel - the Neutral is part of the circuit normally, it is A (as opposed to the only) return path to the source. The process of grounding ( earthing) is primarily for safety, but has other benefits when well applied, such as affecting power quality, noise, etc.
     
  18. Oct 20, 2015 #17

    dlgoff

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    From the same website that I posted the previous images from ...
    Understanding how electricity flows through a circuit
     
  19. Oct 20, 2015 #18
    So I've been researching and have found that the load tries to get back to it's place of origin; not the ground. That's why its called the neutral.
     
  20. Oct 20, 2015 #19
    Thanks for the X1 to X0 to Ground then where? That what i was thinking while posting what i said. But then what happens in case of fault? Like when lightning strikes or in case of insulation failure of appliance where current leaks to the appliance body and could give the user a shock if the appliance isnt grounded.

    Like the current indicated by green arrow in the diagram. That current goes to ground but doesnt return to the appliance from where it is leaking.

    Maybe there must be two separate grounds: one at load end and one at secondary transformer:

    808ecm13fig3.gif

    Any insight would be helpful...
     
  21. Oct 21, 2015 #20

    dlgoff

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    You are asking a very important question here. You should go through all of the Grounding vs Bonding parts. I'll provide some quotes, followed by images, that I consider high points from those parts.

    .
    .
    .
    503ecm17fig3.jpg

    505ecm17fig1.jpg


    505ecm17fig3.jpg

    this quote and image is from http://ecmweb.com/content/earth-not-bonding-jumper
    0101ecwb01fig1.gif

    I hope this will give you an idea of the considerations. That's why there are electrical codes ... to minimize risks.
     
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