A few elementary questions

[MDL]

Hello everyone, I don't know if this is the best place to ask, but I
just had a few questions about elementary wiring / circuits topics

Firstly, when looking at a circuit diagram with a voltage sourse in it,
which terminal of the voltage source / battery is the flow of
electricity coming from? I was told that the positive terminal is the
terminal with a higher potential and is thus the origin of the
electricity, but I was also told that electrons flow from the negative
terminal. Which is correct? The flow of electricity is essentially
the flow of electrons, right? I've heard of "conventional current"
which is the flow of the holes left by the electrons as they move in
the opposite direction (er, I think.). Does this somehow factor into
this topic?

Secondly, What purpose does a ground/earth connection serve in an
electrical circuit? I've heard its a safety device. If so, how does
it function as a safety device, and if not, what is the significance of
it?

Thanks a lot everyone!!

 

[Chris]

Hello everyone, I don't know if this is the best place to ask, but I
just had a few questions about elementary wiring / circuits topics

Firstly, when looking at a circuit diagram with a voltage sourse in it,
which terminal of the voltage source / battery is the flow of
electricity coming from? I was told that the positive terminal is the
terminal with a higher potential and is thus the origin of the
electricity, but I was also told that electrons flow from the negative
terminal. Which is correct? The flow of electricity is essentially
the flow of electrons, right? I've heard of "conventional current"
which is the flow of the holes left by the electrons as they move in
the opposite direction (er, I think.). Does this somehow factor into
this topic?

Secondly, What purpose does a ground/earth connection serve in an
electrical circuit? I've heard its a safety device. If so, how does
it function as a safety device, and if not, what is the significance of
it?

Thanks a lot everyone!!

Hi, MDL. You're in the right newsgroup to ask these questions --
actually, they're two of the most popular questions, and have been
asked and answered many times.

Since you're a Google Grouper (join the throng!), look at the group
homepage. In the "search this blog" box, type in:

"conventional current"

with the quotes for answers to the first question, and

earth +ground

for answers to the second.

Good luck
Chris

 

[John Popelish]

Hello everyone, I don't know if this is the best place to ask, but I
just had a few questions about elementary wiring / circuits topics

Firstly, when looking at a circuit diagram with a voltage sourse in it,
which terminal of the voltage source / battery is the flow of
electricity coming from? I was told that the positive terminal is the
terminal with a higher potential and is thus the origin of the
electricity, but I was also told that electrons flow from the negative
terminal. Which is correct? The flow of electricity is essentially
the flow of electrons, right? I've heard of "conventional current"
which is the flow of the holes left by the electrons as they move in
the opposite direction (er, I think.). Does this somehow factor into
this topic?

The answer depends on whether you are doing electronics or physics.
Electricity and electronics define current as the net movement of
charge, without worrying about what is the actual sign of the charge
that is moving. It assumes positive change is moving, so passive
current is a movement from the more positive to the less positive
node. Inside the source, charge is assumed to be actively pumped back
from the less positive end to the more positive end, by some energy
source. If the current is actually made up of electrons (and in
metals, this is the case), they go the other way.

Secondly, What purpose does a ground/earth connection serve in an
electrical circuit? I've heard its a safety device. If so, how does
it function as a safety device, and if not, what is the significance of
it?

Ground has at least 3 purposes.

The node called ground is a common reference point for many measured
potentials, regardless of whether it is actually connected to the
Earth, or not. Surrounding a circuit with a metal box at the common
potential keeps external noise out and internal noise in. The Earth
can also be a signal or power return path between separate pieces of
equipment. The old telegraph signals were sometimes sent along one
wire by this method, which required a good ground connection at each end.

An earth ground connection drains away static charge build-up.

If the circuit includes dangerously high voltage that is sourced from
a supply that has one end r the other connected to Earth, somewhere
else, surrounding that circuit with a grounded conductive container
prevents you from touching any dangerous voltage in the circuit. where
you would complete a circuit through the Earth. back to the source.

 

[DJ Delorie]

which terminal of the voltage source / battery is the flow of
electricity coming from?

The flow of electrons travels from the negative terminal, through the
circuit, to the positive terminal.

The "flow" of "holes" (places in the atoms where electrons would be,
if there were there, but they're not) goes the other way.

"voltage" is a made-up concept we use to measure the force behind
these flows; by convention, electrons flow towards higher (more
positive) voltages, and holes flow towards lower (more negative)
voltages. Diode symbols, for example, point in the direction of hole
flow.

Secondly, What purpose does a ground/earth connection serve in an
electrical circuit? I've heard its a safety device. If so, how
does it function as a safety device, and if not, what is the
significance of it?

Earth ground serves as a dump for excess current which enters the
circuit through unexpected sources, such as lightning or wiring
shorts. It's a safety device for you if/when it has lower resistance
than your body (at least, restance between it and other things you
might be touching, like the floor), so it's important to get it right.
For ESD protection, it can act as a safety device for your circuit by
giving spikes somewhere to go other than through your circuit.

 

[John Larkin]

Hello everyone, I don't know if this is the best place to ask, but I
just had a few questions about elementary wiring / circuits topics

Firstly, when looking at a circuit diagram with a voltage sourse in it,
which terminal of the voltage source / battery is the flow of
electricity coming from? I was told that the positive terminal is the
terminal with a higher potential and is thus the origin of the
electricity, but I was also told that electrons flow from the negative
terminal. Which is correct? The flow of electricity is essentially
the flow of electrons, right? I've heard of "conventional current"
which is the flow of the holes left by the electrons as they move in
the opposite direction (er, I think.). Does this somehow factor into
this topic?

Secondly, What purpose does a ground/earth connection serve in an
electrical circuit? I've heard its a safety device. If so, how does
it function as a safety device, and if not, what is the significance of
it?

Thanks a lot everyone!!

By convention, charge flows from positive to negative. This is
"conventional current", the opposite from electron flow. Electrons
have negative charge. That's the way it's done, so you'll just have to
get used to it.

Suppose you touch, say, a washing machine, and internally a wire
inside has become shorted to the frame. If the frame is grounded, the
current flows through the ground wire away from you, and a fuse
probably pops somewhere. Without the ground wire, the current path
would be through *you*, and by the time a fuse blew you'd be long
dead.

John

 

[James Thompson]

Hello everyone, I don't know if this is the best place to ask, but I
just had a few questions about elementary wiring / circuits topics

Firstly, when looking at a circuit diagram with a voltage sourse in it,
which terminal of the voltage source / battery is the flow of
electricity coming from? I was told that the positive terminal is the
terminal with a higher potential and is thus the origin of the
electricity, but I was also told that electrons flow from the negative
terminal. Which is correct? The flow of electricity is essentially
the flow of electrons, right? I've heard of "conventional current"
which is the flow of the holes left by the electrons as they move in
the opposite direction (er, I think.). Does this somehow factor into
this topic?

Secondly, What purpose does a ground/earth connection serve in an
electrical circuit? I've heard its a safety device. If so, how does
it function as a safety device, and if not, what is the significance of
it?

Thanks a lot everyone!!

Another analogy you can use: the positive side is like a vacuum that sucks
up electrons, the electron movement is called current. Look at the arrow on
diodes and transistors as pointing toward the vacuum source. By thinking of
the positive as a vacuum, it leads to the term Depletion meaning less of or
an absence of. So depletion in electronics means an absence of electrons.
Anyways Grab hold of the idea that electricity flows from the negative to
the positive and see the arrows as the side that sucks the electrons in. The
arrow side of a diode will be where the electrons are going as in a voltage
rectifier. Think of holes as an absence of electrons and as such is
positive. And the arrow points to where the electrons are coming from. Hope
that helps some. JTT

 

[MDL]

Thank you for the responses everyone, I think I've gotten it. I would
just like to clarify a couple of things:

Suppose you touch, say, a washing machine, and internally a wire
inside has become shorted to the frame. If the frame is grounded, the
current flows through the ground wire away from you, and a fuse
probably pops somewhere. Without the ground wire, the current path
would be through *you*, and by the time a fuse blew you'd be long
dead.

1. Is this current a flow of electrons being suctioned up from the
earth through "you", or the opposite, the electrons are sucked out of
the device into the earth? Since electricity flows from areas of high
potential to lower potential, and is always trying to move to the Earth
(I think), would I be correct to say that the (conventional) current
flows from the device to the Earth? (when actually electrons are moving
from the Earth to the device?)

2. Also, is the ground wire in this example connected to the frame of
the device, or rather the circuit inside of the device?

3. Also, when an electrical device has a standard outlet plug with two
terminals and a ground, where does that ground wire ultimately connect
to? Does it connect to the circuit contained in the device, or rather
some portion of the frame of the device? A good example I suppose,
would be a typical power bar.

4. Finally, again concerning the washing machine example in particular,
in the case that there is no ground wire (or even where there is), how
can the electricity flow through "you" between Earth and the device if
there is no return path?

 

[Michael A. Terrell]

Thank you for the responses everyone, I think I've gotten it. I would
just like to clarify a couple of things:


1. Is this current a flow of electrons being suctioned up from the
earth through "you", or the opposite, the electrons are sucked out of
the device into the earth? Since electricity flows from areas of high
potential to lower potential, and is always trying to move to the Earth
(I think), would I be correct to say that the (conventional) current
flows from the device to the Earth? (when actually electrons are moving
from the Earth to the device?)

2. Also, is the ground wire in this example connected to the frame of
the device, or rather the circuit inside of the device?

3. Also, when an electrical device has a standard outlet plug with two
terminals and a ground, where does that ground wire ultimately connect
to? Does it connect to the circuit contained in the device, or rather
some portion of the frame of the device? A good example I suppose,
would be a typical power bar.

4. Finally, again concerning the washing machine example in particular,
in the case that there is no ground wire (or even where there is), how
can the electricity flow through "you" between Earth and the device if
there is no return path?

The neutral and safety ground are bonded at the main service
disconnect, near the meter and grounding system for a building. If they
are tied together anywhere else, it defeats the concept of a safety
ground.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

 

[Bob Myers]

1. Is this current a flow of electrons being suctioned up from the
earth through "you", or the opposite, the electrons are sucked out of
the device into the earth? Since electricity flows from areas of high
potential to lower potential, and is always trying to move to the Earth
(I think), would I be correct to say that the (conventional) current
flows from the device to the Earth? (when actually electrons are moving
from the Earth to the device?)

Doesn't make any difference, not in the slightest. I'd have to take
some issue with the statement that "electricity flows from areas of
high potential to lower potential, and is always trying to move to
the Earth." The latter part of that is incorrect, or at the very
least irrelevant - "electricity" will always flow (given a conducting
path) between any two points of differing electrical potential. If
one of those points happens to be the Earth, fine, but there's
nothing magical about the Earth that somehow "draws electricity"
other than the fact that it's a very large (and therefore convenient)
reference point. And which point is of "higher" potential really is
only relevant if you ARE concerned with which way the current
(or charge carriers) are moving. You often are concerned about
that, but not in this case.

3. Also, when an electrical device has a standard outlet plug with two
terminals and a ground, where does that ground wire ultimately connect
to?

In the case of most U.S. home situations, the ground wire at the
breaker box end connects to an actual "grounded" point - a
conductor which is buried in the earth. This is the same point
to which the neutral (white) wire ultimately connects to as well.
At the appliance end, the ground (green) wire most typical conducts
to the conductive frame and/or case parts of the device. If there
is no such overall frame/case connection, there may not be a
dedicated "safety" ground, or else it may connect to a dedicated
"safety ground" area of the PC boards, etc., within the device.
U.L. (and others) have some very strict requirements about
where and how these connections are made when a safety
ground wire is provided/required.

4. Finally, again concerning the washing machine example in particular,
in the case that there is no ground wire (or even where there is), how
can the electricity flow through "you" between Earth and the device if
there is no return path?

The Earth IS the return path, by virtue of the neutral connection
going to the ground point at the breaker box, per the above.


Bob M.

 

[Greg Neill]

Thank you for the responses everyone, I think I've gotten it. I would
just like to clarify a couple of things:


1. Is this current a flow of electrons being suctioned up from the
earth through "you", or the opposite, the electrons are sucked out of
the device into the earth? Since electricity flows from areas of high
potential to lower potential, and is always trying to move to the Earth
(I think), would I be correct to say that the (conventional) current
flows from the device to the Earth? (when actually electrons are moving
from the Earth to the device?)

Appliances are generally powered by Alternating Current,
so the electrons flow in both directions alternately.

Also, it should be understood that it doesn't matter
what the charge carriers are, or if they are positive
or negative. Current flow whether "conventional",
that is assumed to be positive charges moving from
+ to -, or if they are electrons moving from - to +,
makes no difference to the analysis of circuit action.

2. Also, is the ground wire in this example connected to the frame of
the device, or rather the circuit inside of the device?

The ground wire for appliances is always connected to
the frame of the device.

3. Also, when an electrical device has a standard outlet plug with two
terminals and a ground, where does that ground wire ultimately connect
to? Does it connect to the circuit contained in the device, or rather
some portion of the frame of the device? A good example I suppose,
would be a typical power bar.

Ultimately the ground wire will connect back to the
entry panel (fuse or circuit-breaker panel) and hence
to a grounding rod driven into the Earth.

4. Finally, again concerning the washing machine example in particular,
in the case that there is no ground wire (or even where there is), how
can the electricity flow through "you" between Earth and the device if
there is no return path?

There would need to be a complete circuit. But such
can be provided by you standing in a puddle of water
leaking from the (dangerously deteriorated!) washing
machine and contacting another grounded object, the
concrete floor, or by you happening to also touch a
water tap or another grounded appliance.

 

[w_tom]

Same wires are common to different grounds. This post will
demonstrate many different ground that share common connections. Each
ground may have different center reference points.

Center point of safety ground is found in the mains breaker box.
All 'grounded' appliances connect to this bus bar. For example, that
washing machine frame connects (via third prong and green ground wire)
hardwired to that bus bar. Earthing electrode (ground rod) and cold
water pipes connect to that safety ground bus bar. All neutral (AC
white wires) also connect to that bus bar.

Only common connection between safety ground wires and neutral wire
is that bus bar. That bus bar is the center of safety ground - and why
anything connected (bonded) to ground can cause a circuit breaker to
trip - for human safety. Everything that connects directly to that bus
bar will stay voltage limited (typically less than 2 volts) which means
human is not harmed.

Meanwhile, to interconnect electronics, electronic appliance voltages
should not 'float' excessively. Best way to interconnect electronics -
especially those using common mode signaling such as printers and
RS-232 devices - is for all electronic components to share a common
ground. In this case, we are using the same safety ground wires for
another ground purpose. But this time, electronics 'common' ground is
(for example) a three prong power strip. Since all appliances share a
single point ground (power strip) - and wire distance here is important
- then ground loops do not exist. Therefore hum or noise that would
interfere with audio or data signals would (should) not exist.

A same green safety ground wire is also routed to become a 'common'
ground between electronic boxes. In this case, center of that ground
system is a power strip.

Meanwhile, inside electronics appliance may be two separated ground
systems on same printed circuit board. Analog ground and digital
ground may remain separated on the pc board except at one point where
both meet. Both grounds remain separated to reduce noise problems.
Generally (but not always), that pc board ground then connects to
safety (green wire) ground. Just another ground that centers, this
time, at a point where analog and digital grounds meet. A ground that
may or may not also connect to building safety ground.

Utility is responsible for another ground that should be inspected:
http://www.tvtower.com/fpl.html
Owners of jacuzzis and swimming pools who suffered electrical shocks
may be familiar with this ground. Another and different ground that is
also connected to that breaker box 'bus bar' safety ground.

Different ground that share common connections. Most of your
responses only discussed safety ground - such as why the washing
machine would trip a circuit breaker and not harm a human.

 

[[email protected]]

By convention, charge flows from positive to negative. This is
"conventional current", the opposite from electron flow. Electrons
have negative charge. That's the way it's done, so you'll just have to
get used to it.

In metals, electrons flow. In other types of conductors (such as
human bodies) there are no electrons flowing, instead there are
positive particles and negative particles both flowing, but in opposite
directions. The positive particles are mostly sodium ions, and
the negatives are mostly chloride.

So, how would we describe the direction of an electric current in
a human body (or in salt water, or in battery acid?) In that case
there is no single direction for flowing charges. If we choose
either direction is the "real" direction, half the carriers will still
be flowing the "wrong" way.

Or in other words, we cannot determine the direction of current
by only looking at the physical motion of flowing charges.

On the other hand, if positive charges flow forward, this gives us
a positive current, while if negative charges flow backward, this
also gives us a positive current.

So the answer is simple: positive current adds the two flows
together, then ignores the actual motion of the charges. It adds
the forward positive charge motion to the backwards negative
charge motion.

And finally, note that ammeters cannot detect the motion of
the moving carriers. An ammeter only measured the magnetism
surrounding the conductors, so it has no way to tell whether the
current is made of backward-moving electrons or forward-moving
protons (or made of two populations of opposite ions which
flow in opposite directions.)

So what is the *real* direction of electric current? Simple: it's
the direction that your ammeter measures. And if you really
want, you can reverse the leads of your ammeter, then measure
all currents as negative numbers. But obviously the reversed
terminals and the negative numbers cancel out (they get
multiplied together, negative times negative equals positive.)

((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty http://staff.washington.edu/wbeaty/
Research Engineer UW Chem Dept, Bagley Hall RM74
[email protected] Box 351700, Seattle, WA 98195-1700
ph:206-543-6195 fax:206-685-8665

 

[Ohm]

Thank you for the responses everyone, I think I've gotten it. I would
just like to clarify a couple of things:


1. Is this current a flow of electrons being suctioned up from the
earth through "you", or the opposite, the electrons are sucked out of
the device into the earth? Since electricity flows from areas of high
potential to lower potential, and is always trying to move to the Earth
(I think), would I be correct to say that the (conventional) current
flows from the device to the Earth? (when actually electrons are moving
from the Earth to the device?)

As John Poplish mentions, an earth ground was used in telegraphy
as a common ground but supposedly not for very long since the ground
conditions varied by location. Some telegraphers allegedly had to
pour water on their grounding rods to make them work. And there were
other problems associated with using an earth ground as a common
circuit ground.

2. Also, is the ground wire in this example connected to the frame of
the device, or rather the circuit inside of the device?

An earth ground is often used as a sort of land fill for
disposal of unwanted, unused, or unexpected energy.
Sometimes it's used as a circuit's common ground,
but that's not common (sorry, resistance is futile).

An earth ground apparently has many other uses, shielding, reflecting, ...

3. Also, when an electrical device has a standard outlet plug with two
terminals and a ground, where does that ground wire ultimately connect
to? Does it connect to the circuit contained in the device, or rather
some portion of the frame of the device? A good example I suppose,
would be a typical power bar.

4. Finally, again concerning the washing machine example in particular,
in the case that there is no ground wire (or even where there is), how
can the electricity flow through "you" between Earth and the device if
there is no return path?

What is "flowing through" wires is mainly energy,
not electrons or positive ions. Sometimes in A.C.,
potentials might be attributed a linear momentum
through wires.

Also "flow through" has questionable meaning for
resistors and capacitors since what didn't "flow through"
them may have been converted to heat, potentials, ...

 

[[email protected]]

MDL wrote:

1. Is this current a flow of electrons being suctioned up from the
earth through "you", or the opposite, the electrons are sucked out of
the device into the earth?

Note that dirt is an electrolytic conductor, so during an electric
current withing the Earth, no electrons flow. Instead, atoms with too
many protons flow one way, while atoms with too many electrons flow the
other way. You can *try* to create electron currents in the Earth,
but the electrons will only survive for a few nanoseconds before being
grabbed by atoms and turning into negative ions. And then, the
presence of all those negative ions will attract the positive ions
already in the dirt, causing a flow of positives. (And of course the
excess negatives start repelling each other, so they flow the other way
as they spread out.)

Confusing? Situations like the above are the reason why we use
"conventional charges" which flow as a "conventional current." We
assume that during any currents, all the flowing charges have the same
sign. Centuries ago we declared the conventional charges to be
positive. (During WWII a large group of technicians tried to change
this to negative conventional charges, but they just succeeded in
confusing thousands of students, as well as creating a population of
technicians who hate those of the "opposite religion": they hate the
community of scientists and engineers.)

Since electricity flows from areas of high
potential to lower potential,

If you employ conventional charges (the positive ones,) then your
statement is right. But if you're a scientist and the *actual*
polarity of flowing charges is important, then you might better say "a
difference in potential causes a flow of charges." That way you don't
have to discuss how many positives flow one way and how many negatives
the other.

and is always trying to move to the Earth
(I think), would I be correct to say that the (conventional) current
flows from the device to the Earth? (when actually electrons are moving
from the Earth to the device?)

Electrons are NOT trying to move from the Earth to the
positively-charged device. The ground wire sucks in negative ions
while simultaneously spitting out positive ions. Electrons do flow up
the wire towards the device, and at the surface of the ground-rod there
are chemical reactions. The chemical reactions are the spot where
positive ions flow out into the dirt, negative ions flow from the dirt
to the metal, and electrons flow from the reaction sites and migrate
into the metal.

4. Finally, again concerning the washing machine example in particular,
in the case that there is no ground wire (or even where there is), how
can the electricity flow through "you" between Earth and the device if
there is no return path?

There always has to be a return path. If you're barefoot on damp
concrete, you're electrically connected to ground. If you're wearing
shoes, but the floor is wet and your shoe soles are wet, then you're
also grounded. Better wear some rubber-soled platform shoes, the kind
Nikola Tesla wore. (Hmmm, Tesla's lab was like the one in the
Frankenstein movies, even having a retractible roof and giant lightning
towers. So why did Frankenstein's Monster end up wearing the
thick-sole rubber shoes? It shouldhave been Dr. Frankenstein who was
clomping around in those things!)

((((((((((((((((((((((( ( ( (o) ) ) )))))))))))))))))))))))
William J. Beaty Research Engineer
[email protected] UW Chem Dept, Bagley Hall RM74
[email protected] Box 351700, Seattle, WA 98195-1700
ph425-222-5066 http//staff.washington.edu/wbeaty/