Basic question about circuit diagrams and ground

[Leros]

I'm confused about the ground connection on circuit diagrams.

Lets talk about DC circuits first. Example diagram It shows a connection to the positive terminal of the battery. Does the ground connection mean the negative battery terminal?

Now, lets talk about AC. You have three wires (plus, minus, and ground) or two wires (plus, minus). How does that work?

 

[funkymatt]

there's a difference between DC and AC. you should read up on those.

 

[Leros]

Originally posted by: funkymatt
there's a difference between DC and AC. you should read up on those.

I know that. I'm actually a EE major, they just never taught us how to deal with this. I do all my work breadboarding with a "ground" connection.

 

[Wonderful Pork]

there is also a difference between common and ground as well, they are not always the same.

DC has voltage(+) and return (-), AC has Line/Live(+), Neutral(-), and Ground.

EDIT: I took a look at the picture...all those ground symbols just show that those pins/lines should be common'd together, not necessarily tied to earth ground. As they are going to the return line of the battery everything will be OK.

If you are trying to add another Power Source to that circuit (hopefully not AC!) make sure that common is tied in to the others.

 

[Leros]

Originally posted by: Wonderful Pork
there is also a difference between common and ground as well, they are not always the same.

DC has voltage(+) and return (-), AC has Line/Live(+), Neutral(-), and Ground.

So for DC, the ground symbol would mean return (-)?

For AC, what is the difference between ground and neutral?

 

[Wonderful Pork]

Originally posted by: Leros

Originally posted by: Wonderful Pork
there is also a difference between common and ground as well, they are not always the same.

DC has voltage(+) and return (-), AC has Line/Live(+), Neutral(-), and Ground.

So for DC, the ground symbol would mean return (-)?

For AC, what is the difference between ground and neutral?

Common, Return, and Ground are not the same necessarily thing and should not be used interchangeably (though they often are).

Common is simply a common point that all the traces/pins connect to.
Return is the (-) side of a DC power supply.
Ground is earth ground. A battery (-) [return] is not grounded unless its physically connected to earth ground or chassis ground.

Yes, many people (myself included) use the word "ground" to mean either common or return, but they are not necessarily grounded in the technical sense.

Most of the time, all of the common points are tied to the return line of the DC power supply, which is grounded, bringing them all to the same potential. Several circuits just have common tied to return but aren't grounded, leaving them floating at a higher (or lower) potential.

AC is completely different from DC as there are multiple voltages (for 3 wire single phase). 3-phase 208V is different from 120V single phase.

EDIT: Ground is kind of nebulous...there are 3 different symbols which refer to 3 different grounds.

The Triangle is signal ground, the 3 diagonal lines (/ / /) is Chassis ground, and the 3 horizontal lines (shown in your link) are earth ground.

 

[Leros]

I'm interested in single phase that you would see in a standard wall connection.

Back to DC. Can we treat this common connection (negative battery terminal) as 0v?

 

[Wonderful Pork]

Originally posted by: Leros
I'm interested in single phase that you would see in a standard wall connection.

Back to DC. Can we treat this common connection (negative battery terminal) as 0v?

You can use it as your ground references for a DMM or something, and measure everything else relative to it. So yes, it would be the 0V point.

 

[Leros]

So, would you consider a 12 volt battery to have:
+12v and 0v terminals
or
+12v and -12v terminals?

Edit: upon thinking, a 12v battery just raises the voltage by 12. So you have
x volts and (x+12) volt terminals

We just consider the return terminal to be 0v because it doesn't matter, only the relative voltages matter?

 

[Wonderful Pork]

Originally posted by: Leros
So, would you consider a 12 volt battery to have:
+12v and 0v terminals
or
+12v and -12v terminals?

There will be only 12V separation between the 2 terminals. You could measure either +12 or -12 depending on the polarity of the DMM.

(btw, the term i was searching for earlier, is floating ground, where everything is common'd but not tied to earth/chassis ground)

EDIT: In response to your edit -> thats exactly correct. Everything is relative if its tied to the same common point. If they don't have the same common/reference point they shouldn't be measured.

 

[BrownTown]

Originally posted by: Leros

Originally posted by: Wonderful Pork
there is also a difference between common and ground as well, they are not always the same.

DC has voltage(+) and return (-), AC has Line/Live(+), Neutral(-), and Ground.

So for DC, the ground symbol would mean return (-)?

For AC, what is the difference between ground and neutral?

Well first off, voltage is obviously a relative term, and when you get into AC its even more relative because the current is flowing from hot to neutral jsut as much as from neutral to hot. But, looking at a standard house type wiring the "ground" is jsut that, tied directly to ground. The "neutral" wire is tied to ground as well, but back at the transformer, the "hot" wire is the one doing the actually doing the 120V AC relative to ground, but if you were just looking at the the "hot" and "neutral" relative to each other they woudl bot appear to be doing 120V AC. If you are hooking this up to an appliance the hot and neutral are what power the device and the ground is connected to the case. That way if there is a fault the case will never be "hot" because it is grounded and it will blow the breaker.

OK, that a terrible explanation.

 

[Leros]

Originally posted by: BrownTown

Originally posted by: Leros

Originally posted by: Wonderful Pork
there is also a difference between common and ground as well, they are not always the same.

DC has voltage(+) and return (-), AC has Line/Live(+), Neutral(-), and Ground.

So for DC, the ground symbol would mean return (-)?

For AC, what is the difference between ground and neutral?

Well first off, voltage is obviously a relative term, and when you get into AC its even more relative because the current is flowing from hot to neutral jsut as much as from neutral to hot. But, looking at a standard house type wiring the "ground" is jsut that, tied directly to ground. The "neutral" wire is tied to ground as well, but back at the transformer, the "hot" wire is the one doing the actually doing the 120V AC relative to ground, but if you were just looking at the the "hot" and "neutral" relative to each other they woudl bot appear to be doing 120V AC. If you are hooking this up to an appliance the hot and neutral are what power the device and the ground is connected to the case. That way if there is a fault the case will never be "hot" because it is grounded and it will blow the breaker.

OK, that a terrible explanation.

So ground is just there as a safety purpose and shouldn't really be doing anything if things are working properly?

 

[Leros]

Originally posted by: Wonderful Pork

Originally posted by: Leros
So, would you consider a 12 volt battery to have:
+12v and 0v terminals
or
+12v and -12v terminals?

There will be only 12V separation between the 2 terminals. You could measure either +12 or -12 depending on the polarity of the DMM.

(btw, the term i was searching for earlier, is floating ground, where everything is common'd but not tied to earth/chassis ground)

EDIT: In response to your edit -> thats exactly correct. Everything is relative if its tied to the same common point. If they don't have the same common/reference point they shouldn't be measured.

Thanks for the help Wonderful Pork, you've answered my DC question.

 

[BrownTown]

Originally posted by: Leros
So ground is just there as a safety purpose and shouldn't really be doing anything if things are working properly?

IT depends what "ground" you are talking about. If you are talking about the ground from the wall sockets then that is one of its uses. You could also use it as the reference for a DC power supply for example.

 

[Leros]

Originally posted by: BrownTown

Originally posted by: Leros
So ground is just there as a safety purpose and shouldn't really be doing anything if things are working properly?

IT depends what "ground" you are talking about. If you are talking about the ground from the wall sockets then that is one of its uses. You could also use it as the reference for a DC power supply for example.

What is the difference between the hot and neutral lines of the A/C, I thought they were pretty much identical. If you switched the wires around, the phase would change, but thats it right? My understanding of A/C is very poor.

120v is the RMS value. The voltage actually fluctuates between -170 and +170 (120/.707) in a sinusoidal manner. Correct?

 

[BrownTown]

Originally posted by: Leros

Originally posted by: BrownTown

Originally posted by: Leros
So ground is just there as a safety purpose and shouldn't really be doing anything if things are working properly?

IT depends what "ground" you are talking about. If you are talking about the ground from the wall sockets then that is one of its uses. You could also use it as the reference for a DC power supply for example.

What is the difference between the hot and neutral lines of the A/C, I thought they were pretty much identical. Of course if you switched the wires around, the phase would change, but thats it right? My understanding of A/C is very poor.

Well first are, are you SURE you are an EE?

As for hot vs neutral, like I said the neutral and ground are tied together. If you were looking at the voltage to ground the neutral would ideally be at 0V, the hot wire would be 120V AC.

 

[Special K]

Regarding earth ground - is the entire surface of the earth an equipotential surface?

Also, let's say you take an input AC waveform, and convert it to DC using a diode bridge and a capacitor. Will there be a potential difference between AC "neutral" and DC "ground"?

 

[herm0016]

the earth is considered to be the 0 volt reference. you can reference anything from earth at get a positive number ( i think)??

It is sort of disturbing that a EE program does not teach you about the very fundamental things that govern all of EE. I find this is true at my school also, the senior EE's i have worked with can't build a circuit unless someone tells them exactly how to hook it up, and can't trouble shoot anything. There is a lack of basic understanding.

 

[Leros]

Originally posted by: BrownTown

Originally posted by: Leros

Originally posted by: BrownTown

Originally posted by: Leros
So ground is just there as a safety purpose and shouldn't really be doing anything if things are working properly?

IT depends what "ground" you are talking about. If you are talking about the ground from the wall sockets then that is one of its uses. You could also use it as the reference for a DC power supply for example.

What is the difference between the hot and neutral lines of the A/C, I thought they were pretty much identical. Of course if you switched the wires around, the phase would change, but thats it right? My understanding of A/C is very poor.

Well first are, are you SURE you are an EE?

As for hot vs neutral, like I said the neutral and ground are tied together. If you were looking at the voltage to ground the neutral would ideally be at 0V, the hot wire would be 120V AC.

I've had no hands on AC experience. Only replacing the voltage source in a circuit with a sinusoidal function. My experience with AC is: v = A cos(wt + omega)

We've done enough theory and math to begin talking about application, which is next semester.

 

[BrownTown]

Well there is alot of focus in EE programs on the digital circuits. You should hear the old people I work with moan about how crappy EEs are these days because back in the day an EE degree meant you learned about motors, transformers, and analog relays. But obviously these days EE is alot broader field, digital has replaced analog in a huge number of applications and computers and microelectronics have taken over. So I can understand where there is some pressure to teach microcontrollers and VLSI design and stuff like that. I know I never learned what the hot, neutral, and ground meant in school, but at the same time if you are an EE you really should know something so basic as the electricity in your house.

 

[Leros]

Originally posted by: BrownTown
Well there is alot of focus in EE programs on the digital circuits. You should hear the old people I work with moan about how crappy EEs are these days because back in the day an EE degree meant you learned about motors, transformers, and analog relays. But obviously these days EE is alot broader field, digital has replaced analog in a huge number of applications and computers and microelectronics have taken over. So I can understand where there is some pressure to teach microcontrollers and VLSI design and stuff like that. I know I never learned what the hot, neutral, and ground meant in school, but at the same time if you are an EE you really should know something so basic as the electricity in your house.

It is sad. I see these people at places like DeVry designing and building cool circuits, while people at nice universities can't really do much actual design work.

I'm also in the CS department and I've seen graduate students who can't program at all, but they know all kinds of crazy algorithms.

 

[BrownTown]

Originally posted by: Leros

Originally posted by: BrownTown
Well there is alot of focus in EE programs on the digital circuits. You should hear the old people I work with moan about how crappy EEs are these days because back in the day an EE degree meant you learned about motors, transformers, and analog relays. But obviously these days EE is alot broader field, digital has replaced analog in a huge number of applications and computers and microelectronics have taken over. So I can understand where there is some pressure to teach microcontrollers and VLSI design and stuff like that. I know I never learned what the hot, neutral, and ground meant in school, but at the same time if you are an EE you really should know something so basic as the electricity in your house.

It is sad. I see these people at places like DeVry designing and building cool circuits, while people at nice universities can't really do much actual design work.

I'm also in the CS department and I've seen graduate students who can't program at all, but they know all kinds of crazy algorithms.

Designing basic analog circuits isn't the sort of job that you get paid a lot of money to do, neither is being a basic programmer. Those skills are the type of things people at community colleges learn because they are very simple. The big universities probable assume if they teach you the hard stuff that you can learn the easy stuff on your own. I mean if you can master circuit analysis using Laplace transforms and do Fourier analysis, and can design a complete ALU out of transistors then you are probably smart enough to go the wikipedia and look up what the different ground symbols mean.

 

[silverpig]

Originally posted by: Special K
Regarding earth ground - is the entire surface of the earth an equipotential surface?

Also, let's say you take an input AC waveform, and convert it to DC using a diode bridge and a capacitor. Will there be a potential difference between AC "neutral" and DC "ground"?

The surface of the earth is definitely not an equipotential surface (apparently earth ground can vary by hundreds of volts from place to place), but it's generally considered to be 0V.

 

[Born2bwire]

Originally posted by: Special K
Regarding earth ground - is the entire surface of the earth an equipotential surface?

Also, let's say you take an input AC waveform, and convert it to DC using a diode bridge and a capacitor. Will there be a potential difference between AC "neutral" and DC "ground"?

No, there can be significant potential differences across great distances on the Earth. Not that big of a deal unless you try laying down long distance wires like a telegraph. In the old telegraphs, they used the Earth ground as their potential reference and there could be a few thousand volts difference across long distances.

EDIT: Damn you silverpig! This is what I get for dinking around for 20 minutes on wikipedia after getting the urge to look up telegraph.

 

[Leros]

Originally posted by: BrownTown

Originally posted by: Leros

Originally posted by: BrownTown
Well there is alot of focus in EE programs on the digital circuits. You should hear the old people I work with moan about how crappy EEs are these days because back in the day an EE degree meant you learned about motors, transformers, and analog relays. But obviously these days EE is alot broader field, digital has replaced analog in a huge number of applications and computers and microelectronics have taken over. So I can understand where there is some pressure to teach microcontrollers and VLSI design and stuff like that. I know I never learned what the hot, neutral, and ground meant in school, but at the same time if you are an EE you really should know something so basic as the electricity in your house.

It is sad. I see these people at places like DeVry designing and building cool circuits, while people at nice universities can't really do much actual design work.

I'm also in the CS department and I've seen graduate students who can't program at all, but they know all kinds of crazy algorithms.

Designing basic analog circuits isn't the sort of job that you get paid a lot of money to do, neither is being a basic programmer. Those skills are the type of things people at community colleges learn because they are very simple. The big universities probable assume if they teach you the hard stuff that you can learn the easy stuff on your own. I mean if you can master circuit analysis using Laplace transforms and do Fourier analysis, and can design a complete ALU out of transistors then you are probably smart enough to go the wikipedia and look up what the different ground symbols mean.

Very true.

Which is what I'm doing. I had taught myself basic circuit construction a long time ago. I just never really learned about the ground stuff, which I'm asking now. This summer, I've been doing several projects with Atmel and Motorola microcontrollers because I've really enjoyed the basic stuff I've doing with them and I'm looking at going into CE (automation and robotics, to be specific).