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Grounded Electricity

  1. Jul 15, 2004 #1
    "Grounded" Electricity

    Well I've checked a few sites for the answer but I still don't seem to understand the grounding as well as I'd like to. I understand that it literally means a wire that goes into the dirt. What I don't understand is where the electrons go after that. Or what they are doing in a socket before you plug something in.

    Lets say we were talking about water. If you "grounded" water, it would just sit there and get soaked up and eventually go away. When you arn't using a spicket, the water is sitting there waiting to be used. But before you plug something in, is the electricity sitting there at the end of the wire or is it moving elsewhere? Thanks.
     
  2. jcsd
  3. Jul 15, 2004 #2
    Grounding allows a current ( temporary) to flow between the object and ( earth , water pipe, etc.) IF there were a voltage between them -- like discharging a capacitor,
    This ensures that the volt difference is close to zero to eliminate accidental shock.
    The Main AC supply has one conductor close to ground ( third prong) it is this one which must be used for internal 'grounding of cases etc. , but in many instances there is no ground wire( two prong) but one is close to ground potential.
    Don't play around with this if your not sure.
    Grounding of RF equipment has to do with antennas, the earth acts like a large slightly imperfect mirror and vertical antennas form half the total ( the mirror the rest ) which is why many such antennas are 1/4 wave as opposed to what they should be 1/2 wave. ray.
     
  4. Jul 15, 2004 #3

    chroot

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    Ordinarily the ground wire does absolutely nothing. No electrons flow through the ground wire at all under normal circumstances. Remember that only a few decades ago plugs only had two prongs, with no ground.

    The ground wire is important only for safety reasons. I'll quote from howstuffworks.com:
    http://electronics.howstuffworks.com/question110.htm

    - Warren
     
  5. Jul 15, 2004 #4
    Actually 'ground wires' are quite active they are subject to induced voltages from nearby equipment - radio waves , static electrical discharges , lightening and so on -- there is no such thing as a perfect ground , and some 'ground wires have enough voltage to give you a shock -- not usually lethal tho'. Ray
     
  6. Jul 15, 2004 #5

    chroot

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    What you've said about ground wires is true for all wires. Although true, it's not particularly relevant to the discussion.

    - Warren
     
  7. Jul 15, 2004 #6
    You can choose to ignore , but in my opinion we are talking about the meaning of grounding and what a ground wire is like I believe is relevant.
    If youve ever seen the result on equipment of a ground surge you may think differently.
    It is not always true that active wires are treated in the same way as ground wires hence they can be subject to very different conditions. Not only that but you cannot assume all wires are balanced to common mode surges which are often ground induced without connection.
    How many other topics would you like to ignore . Ray.
     
    Last edited: Jul 15, 2004
  8. Jul 15, 2004 #7

    chroot

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    rayjohn,

    The original poster simply asked what a ground wire is intended to do -- that question has been answered. Please stay on-topic. Advanced topics like lightning-strike induced ground surge and RF interference just aren't relevant here.

    - Warren
     
  9. Jul 15, 2004 #8
    From 2 pm to about 2 in the morning yesturday, all I was doing was reading electricity articles on HSW haha. It's so interesting and of course I read that article as well. But I was just thinking that it seems electricity needs to go in a "circuit" but when it goes to the "ground.".. Where's the circuit in that? Does it just go and disperse the electrons in the dirt?
     
  10. Jul 15, 2004 #9

    Njorl

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    There's a saying in circuits, "Grounds of the world unite".

    So, if you see a circuit diagram with a power supply and a device, and the hot side of the supply goes to the device, and both the supply and device also go to ground, there is a circuit, because the grounds are considered shorted to eachother.

    Beware though. In practice, grounds can have slight differences. It isn't enough to hurt anybody, but if your measuring small AC signals, ground loops can ruin hours of data. :devil:

    Njorl

    Njorl
     
  11. Jul 15, 2004 #10

    megashawn

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    Lemme take a crack at it.

    Think of an automobile. Think of the charging system. Generally, the battery which has a positive and negative, has two connections. The negative terminal is attached to the chassis of the car, while the positive connects to all the various powered items.

    If you were to take a light bulb, attach a wire to one terminal on the bulb, and the other end of the wire to the positive, nothing would happen.

    Now, touch the second terminal of the bulb to any metal part of the automobile and current flows from the battery, through the chassis, and into the bulb.

    In this case, the chassis of the car is considered grounded, although it is not connected to the ground. Grounding is basically a term, and while yes homes generally have a ground point somewhere that is planted in the earth, as was mentioned, this is merely for safety purposes.

    Now, a neat trick is to find a nice healthy tomato plant and a multimeter, plug the positive probe of the meter into the plant, somewhere near the top, and put the negative probe in the dirt. Set the multimeter to measure low dc volts, and you should see some numbers, representing the voltage present in the plant.

    It isn't like every electrical device is plugged into the ground, it is more like a method of requiring less wire/circuit traces. In an automobile, and DC device can be powered simply by attaching a positive wire to it, and another which is attached to any bare metal.

    Consider a car stereo. You run a power wire, usually from the fuse box, but we will say from the positive of the battery. Now, if your antenna is properly installed, it serves two purposes. One is to pick up radio channels, and the other grounds your stereo to the chassis of the car. This completes the circuit and allows you to power on your stereo.

    Some of the older, cheaper stereos out there use a thing that is called "Common Grounding" And a two speaker stereo system will only have 5 wires, 1 power(positive), 1 ground(negative), Right speaker positive, left speaker positive, speaker ground.

    In this case, you would install the stereo as I mentioned above, you can attach the ground wire for extra elimination of road noise if needed. To install the speakers, you run one wire from the Left + and one from the Right + to the respective speakers. Then, you can run a single wire to both speakers.
     
  12. Jul 15, 2004 #11

    chroot

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    Car stereos are not grounded through the antenna.

    Running speaker return current through the chassis is a guaranteed way to make your stereo sound like crap.

    - Warren
     
  13. Jul 15, 2004 #12
    Chassis

    Megashawn
    you sometimes also see a wire trailing under the car to scrape the 'ground' this is literally to ground the car chassis since in dry weather it can build up static of 10's of thousands of volts giving quite a sharp shock on leaving the vehicle. Here the car and the real ground act as a capacitor -- the wire discharges it by conducting electrons from one to the other . Ray
     
  14. Jul 16, 2004 #13

    Njorl

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    I remember as a kid, all the cars and trucks had them. Now, I almost never see them. I live in DC, where it is not dry at all (it is a stinking swamp). Do they have them in drier areas still?

    Njorl
     
  15. Jul 16, 2004 #14
    Brrrr

    To Njorl
    I live in Canada Njorl where it varies from being hot and humid to being cold and very dry. Yes they still use grounding wires as the shocks can be really sharp , one trick is to use a Key to touch the metal rather than a finger. :surprise:
     
  16. Jul 16, 2004 #15

    Gokul43201

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    I concur ! Establishing "true" single point ground can be a real hard problem to solve. We had to spend weeks redigning/implementing our grounding scheme because of picovolt noise that came from someone buying soda from the coke machine behind our lab. :eek:
     
  17. Jul 16, 2004 #16

    megashawn

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    I can assure you the car stereo I'm using right now begs to differ.
     
  18. Jul 16, 2004 #17

    chroot

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    I've never had one grounded through the antenna and I've installed probably a half-dozen. Weird. :confused:

    - Warren
     
  19. Jul 16, 2004 #18

    megashawn

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    I've installed alot myself. Consider this.

    The antenna body is metal, more times then not. It threads into the car, also metal. The car, being grounded itself grounds the antenna. The outside metal of the antenna is connected to the part of the antenna which is grounded to the car.

    You don't even have to plug the antenna in to ground the stereo. Touch the ground wire of the stereo to the outside of the antenna, or the outside to the chassis of the stereo.

    This comes in handy especially in newer cars where everything is plastic and it is hard to find a good ground point.
     
  20. Jul 16, 2004 #19

    chroot

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    Hmm I wasn't aware the antenna itself was grounded to the chassis.

    - Warren
     
  21. Jul 16, 2004 #20

    megashawn

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    Well, it is a little known trick, because 9 times out of 10 you already have the power and ground wires hooked up before you plug the antenna in.
     
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