question about a neutral in circuit

Discussion in 'General Electronics Chat' started by zaheerahme, Aug 2, 2012.

  1. zaheerahme

    Thread Starter New Member

    Jul 31, 2012
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    i just want to know that what is a newtral in a electrical engineering . how can we get it . what's work of it . what is the main purpose to get it.
     
    Last edited by a moderator: Aug 2, 2012
  2. Wendy

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    This was neither feedback nor a suggestion, so I have moved it to a more appropriate forum.
     
  3. ErnieM

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    Apr 24, 2011
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    "Neutral" may be referring to the "common" lead in AC wiring. This lead is close in voltage to the actual Earth ground, but as it actually carries current may be offset from Earth ground by some small voltage. It is relatively safe to the touch.

    The (Earth) ground wire also connects to Earth but as it normally does not carry current is should be at Earth potential (voltage). It should be completely safe to the touch.

    The "Hot" wires are the ones that carry the voltage and can be hundreds of volts
    above ground. It is very dangerous to touch.

    The distinction between Neutral and Hot is importaint as a safety issue. Take a conventional screw in type light bulb. The large outer ring with the screw threads should always be connected to Neutral, and the small end connector connects to Hot. This way should your finger slip into the socket the dangerous Hot terminal is farthest away and the smallest part.
     
  4. mcgyvr

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    Oct 15, 2009
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    Just a tip..
    NEVER assume that the electrician wired it (outlet/switch,etc..) properly in the first place..
    You should ALWAYS be alert and treat the neutral to be just as dangerous as the hot lead.. In the perfect world the neutral should be safe and is never mistakenly switched.. This world ain't perfect. Treat both wires as dangerous.
     
  5. ErnieM

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    QFT. Note I said "should be" safe to touch. Before actually touch it test it.

    Trust, but verify.

    Also, lamp wiring has evolved over the years so that even a 2 pin AC plug is polarized to maintain the correct neutral connections. Older lamps do not have this type of plug, and I yet to find a polarized replacement plug so have to make do with what I can buy.

    So don't go poking into any lamps either.
     
  6. GetDeviceInfo

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    Jun 7, 2009
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    the neutral carries imbalanced current. The white wire going to your 120vac lamp is not a neutral, even if it is mistakenly refered to by many. Why, because it carries all the current, defying the definition of neutral.

    A neutral primary function is to balance voltages in a multiphase circuit.

    The fact that it carries any current, makes it unsafe to touch.
     
    Last edited: Aug 2, 2012
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  7. cork_ie

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    Oct 8, 2011
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    Mains AC electrical power is normally generated and transmitted across the country as three phase. The three phases are 120 Deg out of phase with respect to one another and are of identical voltage.
    They are analogous to three ropes tied together at one point and being pulled by three men 120 degrees apart in a circle.As long as the three men are all pulling equally the centre point where the ropes are tied will not move.

    Coming back to three phase power distribution - the three phases connected at the local transformer in Y formation, the centre of the Y is the Neutral point.
    As long as equal power is being consumed on each phase and ignoring things like power factor etc, the neutral point will have no net voltage as the three phases are in perfect balance. However to extract a single phase supply for distribution to local consumers each single phase line is connected to the neutral point and respective phase. With three single phases the power consumed per phase will vary and the neutral point will move a little way one way or another away from the ideal balance point -
    much the same way as the centre point of the three ropes in the analogy above would if one of the guys applied a little more or less pull than the others.
     
  8. Wendy

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    Uh, not sure that is quite right, I highlighted the part I have a little problem with in red. Hot, Neutral, Ground. Neutral and Hot carry the same amount of current, until they hit either the breaker box or the pole. I understand split phase well.

    From the point of view of a 120VAC outlet there is only one phase. There is a larger picture, which is what you are talking about, but until that specific leg hits the common point it is only one phase. This is the part the OP is interested in as I read it.

    While I do not consider Neutral safe, it should never be more than a volt or 3 above ground. I do not consider it safe because of potential wiring errors that could render it hot (even when dead), but when the power switch is turned off on a correctly wired system it will be very close to the same potential as ground.

    For the OP:

    http://en.wikipedia.org/wiki/Split-phase_electric_power
     
    Last edited: Aug 3, 2012
  9. GetDeviceInfo

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    By definition, a neutral only exsists in a 3 or more wire circuit. There is no neutral in a two wire circuit. The neutral may carry all the current in a 3 wire circuit, if one of the series loads is open. This follows the definition of imbalanced load where one phase has current while the other is open.

    A neutral has special consideration in application and code. The white wire returning from a lamp for example, does not have those considerations and is simply a current carrying conductor, no different than the black feeding the load. It coinscidently terminates to the neutral at some point, and as such extends the color standard.

    Considering the definition, If one throws a breaker, that will render the hot side of an open load termination dead. However, a neutral will still be connected (via a load) to another phase. Be aware of this as it has important implications.

    The OP queried 'neutral'. What you describe is not a neutral.

    The CEC uses the term 'identified' to distinguish the difference. Not sure how the NEC handles it. Maybe that's where I diverge? Anyone know the NEC specifics?
     
    Last edited: Aug 3, 2012
  10. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    NEC (2008) definitions
    "Neutral Conductor"
    The conductor connected to the neutral point of a system that is intended to carry current under normal conditions.

    "Neutral Point"
    The common point on a wye-connection in a polyphase system or midpoint on a single-phase, 3-wire system, or midpoint of a single-phase portion of a 3-phase delta system, or a midpoint of a 3-wire, direct current system.

    Fine print.. At the neutral point of the system, the vectorial sum of the nominal voltages from all other phases within the system that utilize a neutral, with respect to the neutral point, is zero potential.
     
  11. t06afre

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    The neutral is most often connected to the water drain pipes in houses. So you may get "connected" to it more often than you know
     
  12. GetDeviceInfo

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    and with a bit of Googling, it appears that the NEC allows the term to be extended to what we Canadians would term 'identified', to distinguish the functionality of this mystery wire.

    Maybe the OP needs to come back and clarify what his specific question refers to.
     
  13. GetDeviceInfo

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    That's the 'bond', not the neutral. The neutral is 'bonded' to earth via a suitable electrode, which is often copper water piping before the meter.
     
  14. t06afre

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    Oh I see a bit of a language confusion. Then I learned about this way back in time in Norway. This naming convention from IEC 60446 was not adopted. We used two "hot" wires and a protective conductor. Normally named earth. In a 3 terminal mains connector. It was no rule saying how to connect the wires other than the earth connection of course
     
  15. GetDeviceInfo

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    yeh, probably another 'regional' speak. I'll tone it down, but I do believe it's justified to reduce confusion.
     
  16. t06afre

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    By reading this I also understand my confusion better. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/hsehld.html This is far from the standard used in my country. The standard used in my country is compatible with the 240 volt receptacle. And the use of a transformer is not common in single-unit houses since the grid is 230 volt. In the picture (linked web site) the "neutral" has the function of the protective earth/ground. But in my country this would be the protective earth/ground cable (green/yellow) connected to the water pipes.
     
  17. GetDeviceInfo

    Senior Member

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    here's an example to help see the difference in what I term the 'identified' wire and a 'neutral'. We sometimes see a 3c cable consisting of a black, red, and white. In the home it is often used with 3 way switches, but also to feed two phase loads with neutral.

    Say the black is connected to one phase, the red to another. The white is being used as a classic neutral, returning the imbalanced current.

    Suppose someone comes along and moves the red wire to a different breaker which happens to be the same phase as the black. Now the white becomes what I term the 'identified' wire, and in this case, is subject to overloading, and code violation.

    Sorry, ain't good with pictures.
     
  18. cork_ie

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    Oct 8, 2011
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    He could actually be correct in some instances. I cannot comment about 120V AC systems as I know nothing about them.

    What I do know is that traditionally 230V AC 50HZ which is standard in Europe had three wires for single phase connections. Phase and neutral were supplied by the utility company and the consumer was required to sink an earth rod to provide an earth (ground), and everything was grounded to that.
    Due to the fact that this earth rod became unreliable over a long period due to corrosion and in very dry weather, it was possible that a house would have no proper ground. As a result it was often the case that the ground was also floating.This could cause all sorts of problems like nuisance ELCB tripping and worse. The standard nowdays where all possible is that the Neutral is grounded at each pole by the utility company, where the neutral is grounded on at least 6 supply poles or underground chamber boxes, the system is considered NEUTRALISED and is considered a suitable earth(ground). As is universally required by installation codes - all pipework ,metal cased switches etc are bonded and may be connected to the neutral in this instance.

    Very interesting Wikipedia article here which explains the concept in detail.
    http://en.wikipedia.org/wiki/Earthing_system
     
    Last edited: Aug 4, 2012
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