AC power supply N and L

Discussion in 'General Electronics Chat' started by anhnha, Jan 4, 2015.

  1. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    In AC power supply, there are two symbols L and N. N is Neutral while L is Live or Line?
    N is Neutral: Does it mean this wire is connected to ground and so it always 0V compared to ground.
    L is Live or Line: what does it mean?
    Thanks!
     
  2. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    Yes, ground and neutral are connected to each other AT THE MAIN (CENTRAL) FUSE BOX only. No connection should be made at additional sub-panels.

    Live (line) carries the AC 120 volts relative to the ground.
     
  3. yousaf4you

    New Member

    Dec 13, 2014
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    Neutral (N) Mean Earth, or Nothing Line and Line (L) it Carry current. it is also called hot line.
     
  4. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Thanks for replies!
    Then the polarity does matter here!
    yousaf4you:
    Does the neutral also carry current and equals the total current from three lines?
     
  5. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That is a little misleading as the Neutral should also carry the same current.
    Ground should not be used as a conductor as it does not normally carry circuit current, only in the event of a fault.

    To OP, if you are referring to say the typical SMPS supplies, they are usually marked Gnd, L and N and can be switched from 120v/230v.
    The L and N should be observed if possible, although the supply functions fine in either connection, there is usually a glass fuse fitted internally in the L conductor.
    In this case the L & N should be observed for safety reasons.
    Max.
     
    Last edited: Jan 4, 2015
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  6. anhnha

    Thread Starter Active Member

    Apr 19, 2012
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    Yes, you are right.
    It is Omron Switching Power Supply S82J with input 120 or 240 VAC (selectable).
    I will use it for PLC .
     
  7. MaxHeadRoom

    Expert

    Jul 18, 2013
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    A small point often overlooked is when these types of supplies are used in N.A. on 240vac where L1 and L2 is 120v WRT GND, a fuse should be placed in both conductors, otherwise the internal fuse only covers one live conductor, also applies where a 120v isolated supply is used.
    Max.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
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    Neutral is typically clamped to earth either where the cable enters the house or at the local substation.

    You will tend to find a very small voltage difference between neutral and earth at the wall sockets - this is the small volt drop resulting from current draw at various outlet points.
     
  9. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    A better way of saying this is that Live (line) carries the AC 120 volts relative to the Neutral(which is connected to Earth in the main panel).

    If the third (Green, Ground) wire is brought to an outlet (like the one below), there is never any current that flows along the Ground wire (unless there is a fault).

    [​IMG]
     
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  10. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    There is a local connection between neutral and ground. Ground itself can be made by pounding an 8 foot rod into the earth. Neutral is then connected to this line thru the ground wire in one and only one place, such as your main breaker box.

    When you encounter a connection (such as the outlet MikeML pictured) the neutral may have a different potential than the ground as there is a real resistance in the cable, so if something is drawing current you will see that.

    Neutral and line and NOT interchangeable for safety reasons. In that socket pictured the neutral is always the larger of the two slots. That is for at least three reasons: it is the standard connection, with one tab larger it cannot be inserted backwards, and it is larger so the "safer" tab is the easiest one to touch with your finger.

    This holds true too in a light bulb socket: the outer threaded part you can easily touch is neutral, the live conductor is deep into the socket.
     
  11. ian field

    Distinguished Member

    Oct 27, 2012
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    Most modern ELCB protection doesn't actually sense fault current in the earth return - it compares current going out on the live with what makes it back via the neutral, obviously if the two are not equal; some of the current is going somewhere it shouldn't.

    Swapping the neutral and earth will trip the ELCB every time.
     
  12. MaxHeadRoom

    Expert

    Jul 18, 2013
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    And many that are not so modern, I saw this over 40yrs ago.

    I guess so!! :eek:
    Max. :)
     
  13. WBahn

    Moderator

    Mar 31, 2012
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    It's larger not because that somehow makes it easier to touch with your finger, it's larger because that means that the neutral physically cannot be inserted into the line socket even if the other pin is bend or broken off entirely.
     
  14. studiot

    AAC Fanatic!

    Nov 9, 2007
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    It can be dangerous to confuse the words line and live.

    Live means switched on and the opposite is dead or switched off. Or in more correct terms connected or disconnected.

    Line refers to one of the conductors of an alternating supply. There may be more than one line - there will be 3 in a 3 phase supply, called L1, L2 and L3.

    This alternating supply need not be mains power it may be the audio feed to the speakers in a public address (PA) system.
    Typically a 70 volt line or 100 volt line is used.

    The line may be live (connected) or dead (disconnected).
     
  15. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Hi, anhnha
    If you have time please watch this video
     
  16. ian field

    Distinguished Member

    Oct 27, 2012
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    Is there an exciting bit it takes forever to get to?!
     
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