# Earth ground for simple DC circuit

Discussion in 'The Projects Forum' started by Lightfire, May 1, 2011.

1. ### Lightfire Thread Starter Well-Known Member

Oct 5, 2010
690
21
Hello,

As you may notice, I only made a simple direct current circuit.Which is composed of a 12V battery and three 12V bulbs.

Now, as you may see there, there's a symbol of ground there. Isn't it symbol of ground? If not, then let's say it's symbol of ground.

Now, here's my question.

1) Is it correct that I have put the ground on negative terminal of a battery?
2) How's it working? I mean what's the essence of having that?

Eh, what ground should I use for a simple DC circuit like this. The AC earth ground? Like this: http://en.wikipedia.org/wiki/File:HomeEarthRodAustralia1.jpg

Or what?

Thank you!

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2. ### anselm New Member

May 1, 2011
4
0
Do away with the extra "earth" symbol, the battery negative IS your ground.

3. ### CDRIVE Senior Member

Jul 1, 2008
2,223
99
Really? and you learned that where?

4. ### Audioguru New Member

Dec 20, 2007
9,411
896
A "ground" in a schematic is just a common reference that voltages are measured from, it is not earth.
Frequently many "ground" symbols are used on a schematic so there are not "ground' wires going all over the place. All the "ground" symbols are connected together in a circuit but are not connected to earth.

5. ### CDRIVE Senior Member

Jul 1, 2008
2,223
99
Lightfire, you're working with low voltage, so ground is not a critical safety issue. It certainly won't hurt to have an earth ground connected to the negative line though. Negative is usually the choice for ground because it's generally accepted that hot is positive. Keep in mind that bi-polarity is found in many circuits, like dual polarity power supplies and Op-Amp circuits. Because of this either positive or negative can be at ground potential.

6. ### BillB3857 Senior Member

Feb 28, 2009
2,402
348
A ground reference is also required by most simulation programs. Without it, simulations throw errors or simply refuse to run.

7. ### GetDeviceInfo Senior Member

Jun 7, 2009
1,571
230
I've always understood that symbol to be chassis.

8. ### Audioguru New Member

Dec 20, 2007
9,411
896
Circuits without a metal chassis or with a plastic housing also use the ground symbols on their schematic so that there are not ground wires all over the place.
An earth symbol has three prongs pinting down into the earth.

9. ### Audioguru New Member

Dec 20, 2007
9,411
896
Circuits without a metal chassis or with a plastic housing also use the ground symbols on their schematic so that there are not ground wires all over the place.
An earth symbol has three prongs pointing down into the earth.

10. ### GetDeviceInfo Senior Member

Jun 7, 2009
1,571
230
my exposure has the inverted xmas tree as meaning 'earth' ground.

11. ### CDRIVE Senior Member

Jul 1, 2008
2,223
99

Yes, this was another of Lightfire's topics where we discussed this very issue.

Last edited: May 1, 2011
12. ### Lightfire Thread Starter Well-Known Member

Oct 5, 2010
690
21
Okay guys.

Can you give me a schematic for a simple dc circuit with a ground system?

I just want to see how it works. (even though i can't)

Thanks!!!

13. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
201
The Pitchfork one is earth ground.
The upside down tree one is common ground of a circuit.
Open triangles are either analog or digital grounds.

14. ### GetDeviceInfo Senior Member

Jun 7, 2009
1,571
230
there you go, words in and it's a pitchfork. I've always viewed it as a distributed buss.

If you look in as many references, you'll see as many claims. I'll be sticking with my version, thankyou.

15. ### BillB3857 Senior Member

Feb 28, 2009
2,402
348
Just wait until you get into a system that has different symbols for "grounds" for "logic signal common", "power distribution common", and "earthing safety ground" A more proper term than "Ground" may be "COMMON", meaning the specific symbol is Common to all circuits using that particular symbol. As already stated, the symbol greatly reduces the complexity of the schematic by inferring points being connected together without having to show the actual wire on the schematic.

16. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Ground has several different meanings, all valid.

When dealing with low voltage DC, the earth has nothing to do with it.

When dealing with high voltage AC, there is almost always a ground, which at some point is connected to the earth.

In your application, ground is the common point, where you put the negative lead of a voltmeter to measure the other voltages.

17. ### GetDeviceInfo Senior Member

Jun 7, 2009
1,571
230
as mentioned in many threads, 'Ground' is probably the most widely misused term. The question is, should we as techs perpetuate the myth. It may seem a mute point, but in the world of power and instrumentation, it's carefully calculated.

'Common' is a generalized term that means what it says, that all points marked as such are interconnected. 'Ground' on the other hand, refers to the desired neutrallity between the circuit and the surrounding environment, which most importantly considers our safety being within that environment.

I understand and tolerate the misuse of the term in common application, but when it comes down to applying power, there's no room for generalities.

How valid is that?

Your Electrical Code declares 'ground' to have a single meaning, as it should, to be positively and securely connected to a grounding electrode.

Ground is nothing but, and for those that offer experience or education, get your terms straight

Last edited: May 2, 2011
18. ### CDRIVE Senior Member

Jul 1, 2008
2,223
99
Wow! Who wudda thunk that this topic would trigger, what appears to be, combat readiness?

19. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Try looking it up elsewhere, the use is valid and appropriate. You may disagree with common usage, but you do not define it. No one person does.

Common may be a better way to describe the common point in circuits, but the definition has gotten very ambiguous over time, and the symbol as I use it is definately used that way. When it comes to applying power with batteries, there are generalities. Electricians and electronics codes diverged quite some time ago.

http://en.wikipedia.org/wiki/Ground_(electricity)

Last edited: May 3, 2011
20. ### marshallf3 Well-Known Member

Jul 26, 2010
2,358
201
In searching I've found that some authentic looking places say one thing and another will say the opposite:
http://digital.ni.com/public.nsf/allkb/11BE00780D41622686256BE5006F04CF
http://www.rapidtables.com/electric/electrical_symbols.htm

In other words it's somewhat of a moot point, left to the knowledge of the circuit designer to use the symbols in a clear enough way that someone else can easily determine which symbol is intended to mean chassis or common ground and which symbol is intended to mean earth ground.