# Gormless Question on Ground

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

1. ### Barbrawl McBribeGuest

Forgive me, I should still be very ignorant in electronics; I have not
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. ### Thomas C. SefranekGuest

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.

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(*)/ (*) Bicycle mobile on 145.41, 448.625 MHz

http://www.harvardrepeater.org

3. ### John PopelishGuest

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
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. ### RichieGuest

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..

richie

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Richie086
http://www.richie086.com

"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
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5. ### Ross MacGuest

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