Neutral

Discussion in 'General Electronics Chat' started by farmfly, Apr 9, 2009.

  1. farmfly

    Thread Starter New Member

    Apr 9, 2009
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    I am new to the trade, and just trying to figure out exactly what a Neutral does. When using a 240, when/why is a Neutral NOT needed?
     
  2. leftyretro

    Active Member

    Nov 25, 2008
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    A neutral conductor is always required. It and the hot conductor are the current carrying conductors to the load. A safety ground wire is also usually used but that carries current only in the event of a short circuit from hot to ground at the load device or possible the cable. Ground and neutral are usually tied together at the power entry service panel so they are at the same voltage potential, they differ in which normally carries load currents.

    Lefty
     
  3. recca02

    Senior Member

    Apr 2, 2007
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    Neutral is used in both cases. The neutral (in US) given at mains comes from center tap of the transformer. However on the primary of this transformer there would also be a neutral. IIRC, connecting two hots gives a net of 240 V since 120 volt hot terminals are out of phase with each other .
     
  4. Wendy

    Moderator

    Mar 24, 2008
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    Actually, while it is available, 220VAC in the States doesn't use neutral. Check out split phase electric power from Wikipedia. The neutral can be used to use either line as a 120 (which is done), but if a machine needs 220VAC in the USA the neutral is ignored, and both hot lines (L1 and L2) along with the ground wire, which is still a safety wire.

    If L1 or L2 short to the case or chassis of the equipment the ground will still do its job, and blow the breaker.
     
    Last edited: Apr 10, 2009
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
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    In a 240V AC system the neutral wire is always used. You can't power anything properly without the neutral wire. You need both the live and neutral wires to power a load.
     
  6. b.shahvir

    Active Member

    Jan 6, 2009
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    Hi, :)

    In brief, it is a conductor use to carry out-of-balance single phase currents on a polyphase system. It is the conductor which can be connected to earth without affecting the voltages of the polyphase electrical power system w.r.t earth which is considered to be at 0 potential.
     
  7. Mike2545

    Active Member

    Mar 26, 2009
    116
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    The neutral line in a 240v circuit is used to balance the load, i.e. pick up any current not shared accross the two hot lines. That is why you see in some instances the two hot (black) lines are of bigger wire size than the neutral (white).
     
  8. Wendy

    Moderator

    Mar 24, 2008
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    This isn't the US system, ours is different. Guess we need to find out where the OP is located.

    To Farmfly,

    What is your country of origin? There is a lot of confusion, because the UK is definately different than the USA.
     
  9. recca02

    Senior Member

    Apr 2, 2007
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    I believe the OP is from US. Their confusion comes from the fact (IIRC the US distribution system for mains) that for 120V(or is it 110V?) neutral (the center tap of the transformer that splits the voltage into two hots of 120V out of phase with each other).
    Still a neutral or more appropriately a return path will be required. Also to provide for out of balance current flow a neutral wire will always be there. Though this neutral will be at the primary of the transformer.
     
  10. mik3

    Senior Member

    Feb 4, 2008
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    You are right, I got confused because he mentioned 240V. However, I think he is from US because he says the neutral is not used at 240V.

    The answer is because the 240V is taken across the two hot wires which are 180 degrees out of phase. Note that each hot wire is 120V with respect to the neutral. Thus (120<0)+(120<180)=240
     
  11. b.shahvir

    Active Member

    Jan 6, 2009
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    :) Isn't the neutral normally on secondary side of distribution Xmer ?......unless if it is a power Xmer feeding an HT Xmission line. Plz correct me if I've it wrong!
     
  12. recca02

    Senior Member

    Apr 2, 2007
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    Hi Shahvir,
    You wud be correct in what you say. But I'm referring to something different.

    I wasn't referring to the distribution transformer. I believe the neutral that the OP and, for that matter, I am referring to are the ones that are given at the mains o/l. The one which provides a return path for the current. Not the one that is earthed in a wye configuration,usually at load side, for sending a out of balance current to ground.

    The one I refer to as neutral(it might not be correct to refer it as that, but it serves the same purpose) is actually just the return path connected to the primary of a single phase transformer which splits the incoming supply into a two phase supply with a center tap.

    IIRC, Thingmaker had a good link explaining this system. Maybe, he can still help us with it.
     
  13. b.shahvir

    Active Member

    Jan 6, 2009
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    Oh yes! this system is commonly used many to supply single phase supply to urban areas in the US. Plz guide me to Thingmaker's link as I'm unable to trace it. Thanx
     
  14. recca02

    Senior Member

    Apr 2, 2007
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    Last edited: Apr 11, 2009
  15. b.shahvir

    Active Member

    Jan 6, 2009
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    Actually, the link depicts a neutral wire on the secondary side just as I had posited in my earlier post! ;)
    The primary side has a single winding with no provision for a return neutral.
     
  16. BillB3857

    Senior Member

    Feb 28, 2009
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  17. recca02

    Senior Member

    Apr 2, 2007
    1,211
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    This 'neutral'(return path) is not something unique to US power system. It is something which is present in all power systems - A path for completing the circuit that often is grounded. On the primary winding the phase will connect to one end and the 'neutral'(which is shown with (-) polarity in figure) will connect to other end.
    The reason I had to mention about US power system is that the OP seems to be making a reference to it. My reply to OP has to do with the necessity of a return path often called as the 'neutral'.
    Thanks, Bill.
     
  18. b.shahvir

    Active Member

    Jan 6, 2009
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    Actually, i was referring strictly to the contents of your link only! :)
     
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