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Gormless Question on Ground

Discussion in 'Electronic Basics' started by Barbrawl McBribe, Dec 25, 2003.

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  1. Forgive me, I should still be very ignorant in electronics; I have not
    even graduated high school yet. :) I hear people are surprised about
    the lack of knowledge of what ground is. I am not. There is an
    appalling lack; it reminds me of the way people treat netmasks in
    routing tables, where almost all of the material is complete bullshit;
    learned things the hard way...Since there is a wire in the circuit
    going into the ground, how does the circuit work? Wouldn't this create
    an open circuit? Moreover, if the ground is on the negative terminal
    (as I usually hear it is), how can it be zero Volts? Why is there no
    difference of potential? Lastly, is it true that current is usually
    not flowing through a ground wire? If so, why? If it's connected to
    the circuitry, shouldn't it always have current flowing through it?
    Very confusing...
  2. The circuit is REFERED to "ground" via this wire connection.
    (Many circuits must have a ground reference.)
    Open circuits are... open, disconnected... Do you mean short circuit?
    Ground is NOT polarity sensitive, it's true many circuits have the negative
    voltage source connected, as in the car battery...
    It is the REFERENCE, so by definition, it is ZERO.
    There is (in theory) NO resistance between the negative terminal and ground,
    therefor there can be NO voltage difference between them.
    Perhaps in house hold AC wiring....
    (The currents run in the supply line and it's return line,
    with NO current HOPEFULLY in the earth ground line.)

    In the car there are LOTS of currents flowing in the "ground" wires.
    Most times that's true.
    Yea, until you get well GROUNDED in the subject.

    | __O Thomas C. Sefranek
    |_-\<,_ Amateur Radio Operator: WA1RHP
    (*)/ (*) Bicycle mobile on 145.41, 448.625 MHz
  3. The word 'ground' has several completely different uses and meanings
    as it is applied to electric circuits. The most obvious is that it
    refers to the average potential of the surface of a planet. In this
    capacity, it is the sink for lightning bolts but also the conductive
    platform you are standing upon when you are holding an electric tool
    or appliance. So it is important that the cases of such devices have
    no or low potential differences with respect to this ground, since
    your body may end up completing a circuit between them. So, for AC
    wiring, there may or may not be a load current carrying wire that is
    near Earth (ground) potential (called a grounded current carrying
    conductor or neutral conductor), but there is good reason for there to
    be a wire that runs to a good Earth connection to carry to ground any
    current that would otherwise find a path to ground through your body.
    This is the safety ground concept. If a neutral conductor were used
    for this purpose, and it accidentally had its connection to Earth
    interrupted, then the case would pop up to the hot side line voltage
    by the connection through the device to the hot wire. And you would
    get nailed. If the safety ground conductor somehow becomes
    disconnected from Earth, you only have a problem is there is,
    simultaneously, some internal short between the hot side conductor and
    the case. So it is a good idea to check the safety ground conductor
    on your appliance cords for continuity to the case, and also check for
    continuity to Earth to the safety ground socket in your receptacles
    once in awhile.

    A completely different use of the word 'ground' is to refer to a
    common node that all other voltages in the circuit are measured with
    respect to. The body of an automobile is an example of this use of
    the word, ground. There is actually no electrical connection between
    the Earth and the body of a car riding on rubber tires, but the body
    is called ground, because all load voltages (lights, ignition,
    starter, etc.) have some voltage (the battery voltage) with respect to
    this common node. Some cars have been built with the positive side of
    the battery commoned to the chassis, (and all loads are powered by
    voltage that is negative with respect ot this reference node) but now
    days, the arbitrary convention is that it is the negative side of the
    battery that is connected to 'ground'.

    This concept of 'ground' as being a reference node that you measure
    all other voltages against is also used in all battery appliances, and
    transformer isolated devices. In some of these cases, there is also a
    connection to the Earth through a power cord safety ground conductor,
    or through some other connection, like audio cables that connect their
    internal common (ground) to the shell of the connector, which gets
    Earthed when that signal is connected to another piece of equipment
    that is somehow connected to Earth.
  4. Richie

    Richie Guest

    i agree with you there.. when i first started messing with my
    guitar electronics (very basic stuff) no matter how hard i looked i
    could not seem to find a good description of why or how you need a
    ground. Or if there was a description, it usually involved things
    i didn't understand at the time.. It's simple really.

    Since there is a wire in the circuit
    How else would electrons flow? If you have +5v in a circuit, it
    will want to move thru the circuit to a point where there is less or no
    voltage. The point where V=0 is ground. It's simply a point that
    electrons will want to get to so it can reach equalibrium. Dont forget,
    protons, which are positve repel other protons. Electroncs, which are
    negitive, repel other electrons. But a electron attracts a proton, and
    protons attract electrons due to there opposite charges.

    So when u hook up the ground wire to a circuit, your giving the
    electrons a path to flow from a positive to negitive reference point.
    If you chose ground and the voltage input to be +5, no electrons will
    flow and your circuit wont do anything because the two like charges will
    repel eachother.

    Wouldn't this create
    In almost all situations your negitive and ground can be thought of as a
    0 volt point. But when you work with some circuits, such as operational
    amplifiers you will need a ground, positve and ALSO a negitive voltage
    (example = 0v is ground, -12 is negitive voltage, +12 is positive
    voltage).. be sure to not hookup your grounds to negitive terminals in
    these situations, because negitive will not be ground anymore.

    Why is there no
    there is! one is positive and one is zero. The difference is going to
    be = 0 - voltage input.. like if you have 5v input, the difference
    between the input and ground will be 5v.

    Lastly, is it true that current is usually
    No.. not that i am aware of.

    If so, why? If it's connected to

    hope i helped.. i just got my degree in electrical engineering so i am
    still a newbie compared to most of the people here, so i hope i dont
    have this all wrong :) I'm pretty sure i'm right tho..




    "The only thing better than sitting outside and
    playing a banjo is sitting outside playing a banjo
    made of the skulls of people that made fun of you in
    elementry school."
  5. Ross Mac

    Ross Mac Guest

    The terms Common, Earth Ground and Chassis Ground are quite often used
    interchangably and incorrectly...John did a good job of explaining the
    differences. I think, this is where much of the confusion comes to many new
    to the industry.....Ross
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