very basic

Discussion in 'General Electronics Chat' started by rkbestever, Feb 22, 2013.

  1. rkbestever

    Thread Starter New Member

    Jan 27, 2012
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    In our home electrical plug, one is live and other is neutral. But when we do analysis we shows current flowing from line to neutral in first half cycle and from neutral to line in second half cycle as in case of rectifier circuit. Then how it is possible the current flows from neutral to line as it is already ground???
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Current flows in a complete circuit. The neutral is part of that circuit. Its "grounded" (or tied to the actual ground wire) in the fuse panel only.
     
  3. BillB3857

    Senior Member

    Feb 28, 2009
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    The polarity of the live wire changes from positive to negative either 50 or 60 times every second, depending upon where in the world you live. The neutral wire always stays at zero.
     
  4. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    BillB is correct. Neutral never supplies current. You can stick a paperclip into the neutral part of the socket and not get a shock (don't try it though!).
     
  5. BillB3857

    Senior Member

    Feb 28, 2009
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    I'm glad to see the "(don't try it though!)" addition. Beginners should NEVER attempt anything like that. It is too easy (33% chance assuming a U-Ground outlet) to get it wrong if you don't know exactly what you're doing.
     
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  6. radiohead

    Active Member

    May 28, 2009
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    Some things to remember when wiring a replacement AC plug:

    Turn the circuit breaker off before messing with the connections.

    When wiring the plug, black is hot (gold connection to the short slot), white is neutral (silver connection to the long slot) and green or bare is ground (green screw connection to the "D" shaped lug).

    turn the circuit breaker back on.
     
  7. DerStrom8

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    Exactly. There is just too much risk, so I felt it necessary to express the "do not try this at home" factor.

    My post was simply to make a point ;)
     
  8. ErnieM

    AAC Fanatic!

    Apr 24, 2011
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    Actually neutral DOES supply (and sink) current... it never sources voltage which makes it "safer" to touch then the hot leg.

    When the hot leg is positive the current flown into neutral.

    When the hot leg is negative the current flown out of neutral.
     
  9. BillB3857

    Senior Member

    Feb 28, 2009
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    I don't think any of us are saying that neutral does not carry CURRENT. We are saying that it has no potential energy (voltage).
     
  10. #12

    Expert

    Nov 30, 2010
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    Sometimes it helps to look at the bigger picture.
     
  11. vpoko

    Member

    Jan 5, 2012
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    I might be being pedantic here and I know I'm not telling you anything you don't already know, but for the benefit of the OP: a single prong has no voltage at all. Voltage is a pressure difference, so it only exists between two points. Half the time, neutral has negative potential with regard to the hot plug and sinks current, and the other half it has positive potential with regard to the hot plug and sources current. This excludes the very short zero-crossing period where they have the exact same potential and no current flows at all. It being tied to ground doesn't prevent it from being able to push electrons out, as long as its pushing them to somewhere with even lower electrical pressure (half the cycle).
     
  12. DerStrom8

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    Feb 20, 2011
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    I guess I didn't phrase that correctly. Yes, on one half of the cycle the ground "sources" current in the sense that it lends electrons to the circuit. I suppose I should have said voltage in that case.

    Let's think of it that way. When you're standing on the floor, you are essentially connected to ground. Therefore, there is no potential difference between you and the neutral terminal. Since there's no potential difference, there's no voltage to "push" the current. That is why you wouldn't receive a shock.

    I think I'm digressing though. The way the OP was describing it was that on half the cycle 'hot" produces a voltage, and on the other half cycle "neutral" produces a voltage. That is not true. The only voltage potential is produced by the HOT line, with respect to neutral (ground).
     
  13. DerStrom8

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    That is true. If you were completely electrically insulated, you could theoretically touch the hot line and not receive a shock (again though, do not try it). The danger comes when you are touching hot and come in contact with something that has a lower or higher potential than the hot line (i.e. neutral).

    By the way, vpoko, may I ask where in Boston you are? I happen to be living there myself! :D
     
  14. vpoko

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    Jan 5, 2012
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    Jamaica Plain.
     
  15. DerStrom8

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    No way, I'm about 3 miles from you :D I'm in the Greater Boston area, over near the Pru.
     
  16. rkbestever

    Thread Starter New Member

    Jan 27, 2012
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    BillB3857 is saying that "the polarity of the live wire changes from positive to negative either 50 or 60 times every second, depending upon where in the world you live. The neutral wire always stays at zero" then how it is possible that live is also acting as negative.
     
  17. DerStrom8

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    Feb 20, 2011
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    Sorry to answer a question aimed towards you, Bill, but this is an easy one to reply to :D

    rkbestever, negative is not always the same as ground. Negative in this case is -120v, whereas ground is 0v. Positive is 120v (in the US). It's -240 0 240 in europe and most other countries
     
  18. vpoko

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    Jan 5, 2012
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    Great city, don't think I'd ever want to live anywhere else (and hell, I'm saying that immediately following one blizzard and before another).
     
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  19. DerStrom8

    Well-Known Member

    Feb 20, 2011
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    Meh, the city is nice--one of the nicest I've ever worked in--but I don't think I'd want to live here the rest of my life. I'm a country guy. Raised in a small town in Vermont and grew to love it. The peace and quiet, beautiful natural landscapes, wildlife. That's my kind of place. I'm thinking of leaving Boston soon, to go back to my place in VT. We'll see though.

    Okay, sorry for the sidetrack. Back to the thread :D
     
  20. vpoko

    Member

    Jan 5, 2012
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    What I'm about to say isn't going to help the OP understand what he's trying to understand, but just for the sake of the full story: positive is actually closer to 170V and negative is ≈ -170V. 120V is the RMS voltage. For a sine wave, RMS voltage is peak * 1/√2.
     
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