What is ground ?

Discussion in 'Homework Help' started by bhavesh96el, Apr 24, 2006.

  1. bhavesh96el

    Thread Starter Member

    Apr 24, 2006
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    Hi Everyone! I am having a great difficulties in understanding what ground is ? and why do we use ?

    i have understanding of ground as it is used as a common point in a circuit with respect to what we measure the voltage across all other nodes. and it is used for safetly reasons.

    There are various kind of ground. like lightning protection ground , EMI reducing ground..

    now what is Neutral ? what is ground ? why do we use them ? how can we differenciate them ?

    Thank you all..
     
  2. paultwang

    Well-Known Member

    Mar 8, 2006
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    0

    Safety ground
    (ideally) also known as: Earth ground, chassis ground.
    note: You are probably standing on it (Earth ground) right now. Metal chassis should always be grounded by using the ground prong! If safety ground is not Earth ground, you are in deep trouble.

    Circuit common (ground)
    This is a convenient way to tie all points with this circuit ground symbol together. For safe voltage levels or insulated enclosure, this does not have to be Earth ground. There can be more than one circuit ground, due to finite conductance in wires. For example: analog ground, digital ground... so they don't interfere each other.

    In my opinion, circuit common should not be called "ground" at all, if it is kept to itself.


    Different names
    Lightning protection ground is safety ground. Noise reduction ground is safety ground too (Faraday cage).

    Mains neutral IS NOT ground.

    Mains neutral is the current return path. It is very close to Earth potential, but is not designed to be Earth/safety ground.
     
  3. bhavesh96el

    Thread Starter Member

    Apr 24, 2006
    11
    0

    Hi! Yes i did understood that but i can not vision how ground provide saftey ? like if at the first place at power generation plant instead of using ground if we use other conductor cable for reference level.
    so even if hot wire short to chasis and anybody will touch chasis won't complete the circuit eventhough it is on ground ( earth ) because instead of using ground as a reference level we are using something else as a reference from first place.

    Is it make sense ? if yes then why do we use ground ?

    thanks and sorry as i am totally confuse on this topic.


    Regards,
    Bhavesh
     
  4. paultwang

    Well-Known Member

    Mar 8, 2006
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    0
    You are probably aware that when hot touches ground, it shorts out at the service panel, and should blow the fuse/breaker... without anyone touching it.


    In your case, I see a few problems:

    If the entire electrical distribution system is floating off earth ground...

    1. I for one, won't touch any electrical things without a 10-ft insulated pole. We are normally earth grounded, although rather poorly. If we touch something that floats off earth ground, we might get a brief and very nasty electrostatic shock.


    2. Speaking of electrostatic discharge: As our body's and most objects' electrical potential is neutral with respect to earth ground (unless you've been rubbing your feet across carpet), if we grab an ESD sensitive device and plug it into the floating mains outlet, the device may be damaged.


    3. Lightning. A lightning bolt hits your building and induces transient currents on your lines. Where can they go? None of them is earth grounded!!

    "If there isn't a better path to ground, you are the ground!"


    4. In the event that a tree decides to take the power lines down with it...


    5. "Earth is the most omnipresent conductive surface."


    There are more reasons.
     
  5. SparkMan

    New Member

    Apr 27, 2006
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    Ground provides safety because it is an alternative return for power.

    Now if you do any electrical work, you are probably confused with ground, because inside the mains box, Nuetral and ground wires are tied to the same busses.

    The Hot wire (Black) is the supply wire. The Nuetral (White) is the return. Imagine electricity as water, black is the supply line, white is the return, or drain.

    So where does ground play? Okay, lets say you have a power drill, and the outside casing is made of metal. Your drill has a 3 prong plug.

    On the inside, the motor would get the Hot and Nuetral wires, and the case would get the ground.


    Okay, lets say somehow the hot wire inside the drill broke off the motor and touched the metal case:

    You would not get shocked because the ground would become the return path for the electricity, and since it would be a short circuit, the breaker would trip.


    !! Now, here's that safety part: If there was no ground, Guess what? The hot wire, which supplies the electricity, would touch the metal, and since the metal has no path or return for hte electricity, it means that essencially it is the same as the hot wire (We call that, being at the same potential). What this means, is that you are touching hte metal case, so you basically are touching the hot wire, and you would get shocked good.

    That is why they created grounds. (At least, one reason they did). There are many other reasons, but that is the first one I can think of at the moment
     
  6. Grant

    Member

    Mar 5, 2006
    17
    0
    Ground provides safety because it is an alternative return for power.

    Now if you do any electrical work, you are probably confused with ground, because inside the mains box, Nuetral and ground wires are tied to the same busses.

    The Hot wire (Black) is the supply wire. The Nuetral (White) is the return. Imagine electricity as water, black is the supply line, white is the return, or drain.

    So where does ground play? Okay, lets say you have a power drill, and the outside casing is made of metal. Your drill has a 3 prong plug.

    On the inside, the motor would get the Hot and Nuetral wires, and the case would get the ground.
    Okay, lets say somehow the hot wire inside the drill broke off the motor and touched the metal case:

    You would not get shocked because the ground would become the return path for the electricity, and since it would be a short circuit, the breaker would trip.
    !! Now, here's that safety part: If there was no ground, Guess what? The hot wire, which supplies the electricity, would touch the metal, and since the metal has no path or return for hte electricity, it means that essencially it is the same as the hot wire (We call that, being at the same potential). What this means, is that you are touching hte metal case, so you basically are touching the hot wire, and you would get shocked good.

    That is why they created grounds. (At least, one reason they did). There are many other reasons, but that is the first one I can think of at the moment
    [post=16599]Quoted post[/post]​
    [/b][/quote]
    As nobody in this thread identifies their location (I assume SparkMan is in USA from his wiring colour coding), thought I would mention the single phase colours for U.K(new)/Europe, Australia and more use.... brown for active (hot!), blue for neutral, and green/yellow striped for earth conductor.
    Cheers,
    Grant
     
  7. Grant

    Member

    Mar 5, 2006
    17
    0
    repeat
     
  8. paultwang

    Well-Known Member

    Mar 8, 2006
    80
    0
    Not only will you get a shock, you will not be able to let go of the tool because the electricity is disrupting your neuromuscular system.
     
  9. windoze killa

    AAC Fanatic!

    Feb 23, 2006
    605
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    In Australia I believe that Neutral is connected to ground at the sub stations. BUT doesn't mean it is still at ground potential at your home.
     
  10. SparkMan

    New Member

    Apr 27, 2006
    8
    0


    I live in the USA, but I have family in many parts of the world, and there are definently different ways countires go about thier electrical.

    Australia's colours are also typically used in a lot of devices in the USA, for example, some computer PSUs use the brown,blue,green/yellow.

    But its a fair tossup, because you'll see both systems in different devices.

    <!--QuoteBegin-windoze killa

    In Australia I believe that Neutral is connected to ground at the sub stations. BUT doesn't mean it is still at ground potential at your home.
    [/quote]

    I am not sure where they tie the Neutral and Gnd in Australia, in the USA typically they are tied at the mains box, but it brings a good point: Even though it's tied to ground somewhere in the system, never assume Neutral is safe to touch. There are codes for how wiring should be done, but that does not mean that you are guaranteed the wiring in your house is by code (And in the USA, many homes arn't by code, even new ones, its pretty bad here).

    Also, another point: Neutral can possibly become a killer. Just like my example of the drill, if for some reason Neutral becomes disconnected, or open, then the side that is still connected to the circuit (not the side that goes to the mains), is now at the Hot potential, thus you might as well be touching the hot wire.

    Never assume Neutral is safe to touch.
     
  11. alva

    Member

    Dec 14, 2005
    12
    0
    I like the UK/Australian color code better than the US color code where Black=hot. There have been cases where repair work is done by unlicensed people and since more people are familiar with the DC color code of Black=negative and Red or White = positive they wire AC plugs or appliances backwards thinking White wire = positive or hot and Black is ground or neutral thus posing shock hazards for the next person that comes along and messes with it.
    -----------------------------------------------------------------------------------------------



    As nobody in this thread identifies their location (I assume SparkMan is in USA from his wiring colour coding), thought I would mention the single phase colours for U.K(new)/Europe, Australia and more use.... brown for active (hot!), blue for neutral, and green/yellow striped for earth conductor.
    Cheers,
    Grant
    [post=16600]Quoted post[/post]​
    [/quote]
     
  12. bhavesh96el

    Thread Starter Member

    Apr 24, 2006
    11
    0
    [post=16645]Quoted post[/post]​
    [/quote]


    Thank you all for replies on this topic which helped me understand the funda of grounds.

    Regards,
    Bhavesh
     
  13. iamsand

    New Member

    Jan 6, 2007
    2
    0
    Everyone has seems to have avoided Grant's original question, with albit correct information, but not exactly on point. I have been wondering about exactly what he was asking and can't seem to find a clear difinative answer anywhere (including here, so far).

    The question is, what if the power company never connected the neutral conductor to the earth, ever. It would then logically seem that there would be no path back to the "hot" side even if a hot conductor shorted to a metal case and a person were to be standing in a puddle of water bare footed and touched it. Can someone explain how this would be a safety issue? Where would the "hot" current flow to if there were no earth connected grounds in the first place?
     
  14. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,582
    770
    The problem with unearthed power lines is that whenever someone accidentaly touches one of the wires, he makes the connection to "earth". If you don´t have enough luck and are standing few meters from him, and touch the other wire thinking it is safe, you can get zapped both, because the circuit is completed by you standing on the ground.
     
  15. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    The power company has already referenced the distribution lines to earth ground. At some point close to the home, there will be a line run from the power lines to a made earth ground. this is just normal practise.

    But, even in the absence of such a ground wire in the house, the voltage-carrying conductor will still conduct strongly to ground,and will present an electrocution hazard to a person touching it while standing on a grounded surface.
     
  16. iamsand

    New Member

    Jan 6, 2007
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    Thanks for the reply but it still does not address what would happen if the power company never used the earth for refrence in the first place. I am assuming that you are saying that even if there is no ground wire at the house, there would still be a path back to hot through the earth due to the power company's connection to it at the power source. But what if there was no such connection, at the source or anywhere else? Wouldn't that prevent any circuit from being created through the earth (and therefor be a safer situation for us all)?
     
  17. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Hi,

    Only if proper grounding techniques are not followed. If the case is tied to ground or the internal circuit is inherently safe, danger is minimal. With proper case grounding, every surface you touch is at the same potential. No shock hazard exists. Without a ground reference, lightening can raise the potential of all your house wiring such that a potential difference of several tens of thousands of volts exists. Makes it kind of dangerous to be turning on the lights about then...
     
  18. wireaddict

    Senior Member

    Nov 1, 2006
    133
    0
    Another thing to consider about ungrounded/floating power lines is that they won't always remain that way; consider the effect of rain and condensation, or faulty insulators, particularly with higher voltage lines. The odds of the lines staying ungrounded are slim. It's much safer knowing which wire is hot and which is grounded although, as SparkMan said, never assume the neutral is grounded.
     
  19. carrick395

    New Member

    Jun 28, 2016
    1
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    Most houses have 2 circuits or phases supplying power with the neutral grounded. If you come in contact with one phase the max. voltage you would receive (in the USA) is 120 volts. If the other phase became grounded and the neutral was not grounded, then you would be hit with 220 volts. The main reason for grounding the neutral is to limit the voltage for safety.
     
  20. MaxHeadRoom

    Expert

    Jul 18, 2013
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