# Why Do we ground an electronic circuit?

1. Apr 27, 2015

### cbram

Why we use the symbol ground in electronic circuits?
What is the use of grounding

Last edited: Apr 27, 2015
2. Apr 27, 2015

### nsaspook

Which one do you mean?

3. Apr 27, 2015

### cbram

The one which has power ground
What does the power ground do

Last edited: Apr 27, 2015
4. Apr 27, 2015

### davenn

what do you think would be a good reason for having part of the circuit grounded ?

how about googling some of the ground definitions and see what you find out

try these ....

Earth grounding
Power grounding
Chassis grounding
Analog grounding
Digital grounding

come back with the answers you found and any questions on what you may not understand

5. Apr 28, 2015

### cbram

Can any one explain virtual grounding in op amp

6. Apr 28, 2015

### davenn

have you done any of what I asked you to do ?

7. Apr 28, 2015

### cnh1995

If I am not wrong, the power ground is the reference point in the circuit, assumed to be at 0V. It is usually the -ve terminal of the battery in case of single power supply and the mid-potential point (point where -ve of Vcc and +ve of Vee are joined) in the dual power supply. Dual supply will have three voltages, Vcc, GND(assumed 0) and -VEE..

8. Apr 28, 2015

### analogdesign

I think you're confusing power ground and signal ground (although they are often the same). The signal ground is the reference point in the circuit like you said. The power ground is the return path for any current leaving the power supply and energizing your circuit. I work almost entirely with fully differential analog systems and in that case the signal ground is typically VDD/2 or thereabouts even though the system is using a single supply. This signal ground is most certainly distinct from power ground. This definition isn't universal but in my experience it is useful to think of a small-signal ground (which could even be VCC depending on how the circuit is set up) from the current return path.

In case the OP doesn't know how to use google, the short answer is electrical current can only flow a loop, therefore in order for any kind of circuit to do anything there must be a path for electrons to get back to the battery or power supply from which they started.

9. Apr 29, 2015

### meBigGuy

The ground symbol in a schematic generally refers to the 0 volt reference point for the design.

It is convenient to use the ground symbol to avoid drawing lots of lines (since there are so many components connected to the 0 volt reference)

In addition, there can be multiple grounds, such as "analog ground" or "digital ground" or "chassis ground" or "rf ground" or "audio ground", etc etc etc , which become significant in situations where signal isolation or circuit safety become issues.

The virtual ground in an op-amp circuit is not a true ground, and is not represented by a ground symbol. It is a node in an circuit that the op-amp attempts to actively keep at the ground voltage (generally the - input when the + input is grounded). You need to fully understand opamps for that to make sense, so look them up ( http://en.wikipedia.org/wiki/Operational_amplifier ).

10. Apr 29, 2015

### jim hardy

@cbram
We've had many many discussions on grounding, try a pf search.

"Ground" is the most widely misunderstood concept in EE..

Usually in consumer electronics like TV's what you're calling "Ground" is the metal chassis. Logical enough.
I notice most consumer electronics today comes with just a two prong power cord, no ground prng..
With just two prongs there's no connection to earth ground, only to house line and neutral.
Nobody ties chassis to neutral anymore like they did in 1950's. That's because a household outlet might be wired backwards tying chassis to hot. With few exceptions, the power supply insulates chassis from both wires of the power cord.

Now -
in any device there are several circuit branches fed by the power supply. . KIrchoff tells us that currents must flow in closed loops so each branch's current must get back home to the power supply. .
The place where they all meet up to make that last short hop back home is usually labelled "Circuit Common"...
In reality it's no different from any other node , but it's the most convenient place to connect your voltmeter's black wire..
But it may or may not be grounded through the power cord...usually it's not.

So I tell people it's a mistake to call it "Ground" when it's not grounded..
Call it "Circuit Common" instead..That's more accurate..
If it's connected to Mother Earth, call it earth like they do in England. .

I'd like to see the term "ground" disappear because it's so widely misunderstood.
That's partly because of the water analogy we've all heard.
As kids we played in the yard with the garden hose and observed that
1. the water meter is in the ground , and
2. water from the hose falls to the ground and soaks in.
So we're imprinted early that water has some affinity for "Ground" , when it's really just gravity..
We transfer that misconception to electricity..

so try to keep Kirchoff in mind.

"Ground" is just another wire. It goes most everywhere. Airplane electrics operate just fine without it.

old jim.

11. Apr 29, 2015

### XZ923

Jim, I wholeheartedly agree with referring to "ground" as a circuit common instead; you've hit on one of life's greatest aggravations for me. For a perfect example of this application, look at the wiring diagram for pretty much any of the older dirtbike that run off a single-phase AC generator. There are a minimum of three "ground" symbols on the wiring diagram (stator, load, and regulator). This leads to a ton of people claiming that a stator needs to be replaced because it's "shorted to ground" when in fact the chassis is acting as, well, exactly what you say-a circuit common.

Cars, bikes, and as you pointed out airplanes all have "grounds", but they certainly don't have "earths" (despite what many mechanics will tell you). I can just imagine how Lockheed Martin would react if they were told that F-22s must be tethered to the earth by a metal cable.

12. Apr 29, 2015

### jim hardy

and the tires insulate all 3 from "ground".

13. Apr 29, 2015

### jim hardy

i feel almost apologetic for the diatribe
but i've seen soooo many newbie engineers struggle with "ground" that i try to disseminate the idea.....

14. Apr 29, 2015

### psparky

Ask 10 experienced electrical engineers how to ground a complicated system and you will get 10 different answers.

Start talking about ground mats in new buildings for substations and so forth and you will get 20 different answers from 10 experienced engineers.

The NEC code book is no road map as well. It has hints and suggests some wire sizes but always seems to be vague for complicated systems.

I agree that grounding is one of the more confusing things we do. However, you should try to understand the basics.

15. Apr 29, 2015

### XZ923

IMHO it should be taught as part of the basics of voltage. There are a lot of folks I know of who don't grasp that voltage is a difference between two points.

16. Mar 27, 2016

### jim hardy

Well ! Industry is coming around !

http://e2e.ti.com/blogs_/b/precisio...id_pod3=LTI4MzIyNDI0NTQS1&sp_mid_pod3=4968551

17. Apr 6, 2016

### meBigGuy

That doesn't make sense? What opamp ever had an output pin labeled ground?

18. Apr 6, 2016

### Svein

No, but an input pin named GND has been used, especially in old designs. I cannot remember which at the moment, but (as a poor substitute) the LM324 (http://www.ti.com/lit/ds/symlink/lm124-n.pdf) uses GND to designate a power dupply connection.

19. Apr 6, 2016

### meBigGuy

Ground as an input is no issue to me.

I'm referring specifically to this:
"This is because GND is supposed to indicate zero volts, but an op amp never puts out exactly zero volts, making the original label confusing"

What is he trying to say?

It's also wrong because op-amps put out exactly ground lots of times, just never for long [\joke]

20. Apr 6, 2016

### jim hardy

I'd say
he too is confused and mis-uses the term. He's trying to say 'voltage reference point' .

Take him up on his his invitation to drop a line?
I think i will....

old jim