# Understanding Common Floating Return [duplicate]

So I'm pretty new to electronics, and I'm getting slightly hung up on the concept of ground. I'm thinking the circuit diagrams below will help me to explain this frustration, because there's not an intuitive explanation as to why these two diagrams are identical.

I'm just going to spew what I believe is correct, and hopefully I get some stuff wrong and learn along the way.

Looking at the rightmost diagram:

My intuition is that (since these are 0V reference points, not actual ground connections) if electrons flow out of the negative terminal of the battery there needs to be a connection to the right 'ground' in order to keep it at 0V relative to the left ground.

Expanding on that, does that mean every 0V reference point can be thought of as being connected by a wire. So if I had 50 more 0V reference points, throughout some complicated circuit, all of them can be thought of as being connected? Thus simplifying any circuit with multiple 0V reference points to only one 0V reference point?

Question: What is the point of doing this? Is it just to reduce the complexity of circuit diagrams later on? Because right now it definitely complicates the one below.

Secondly, say instead of 0V reference points, those ground connections are actually earth ground connections.

The reason why current would instead flow to the negative terminal of the battery is because it's more attracted to that then the neutral ground. Does any minuscule amount of current leak to ground? Also, in the same sense as before, can we think of each individual 'earth' ground in the right diagram as connected?

Thank you!

## marked as duplicate by Harry Svensson, Trevor_G, Finbarr, RoyC, laptop2dMar 6 '18 at 16:32

• does that mean every 0V reference point can be thought of as being connected by a wire, ....Is it just to reduce the complexity of circuit diagrams later on - YES. – Eugene Sh. Mar 5 '18 at 18:38
• electronics.stackexchange.com/a/356093/139766 – Trevor_G Mar 5 '18 at 18:41
• The concept of ground gets more complicated with AC voltage and current spikes. An Earthed ground is low impedance and wide-spread as opposed to a floating gnd which is not. Inductive and capacitive leakage from external or internal sources can induce floating ground shift noise or induced current with voltage drop into inductive loops including the floating ground. Either way a common mode interference turns into differential noise. This is when shielding, filtering and/or earth ground connections are used to reduce EMI. – Sunnyskyguy EE75 Mar 5 '18 at 19:39
• and in mains electrical wiring, ground means a completely different set of things, with no relation whatsoever to electronics GND. – Harper Mar 6 '18 at 2:33
• Unless your using superconductors, all of those wires have parasitic resistance, capacitance and inductance. – laptop2d Mar 6 '18 at 16:31

My intuition is that (since these are 0V reference points, not actual ground connections) ...

Correct. The reference can be any arbitrary point on the circuit but battery negative is very popular!

.. if electrons flow out of the negative terminal of the battery there needs to be a connection to the right 'ground' in order to keep it at 0V relative to the left ground.

Don't worry about electrons. Just think of "current". The grounds are all connected and at the same voltage.

Expanding on that, does that mean every 0V reference point can be thought of as being connected by a wire. So if I had 50 more 0V reference points, throughout some complicated circuit, all of them can be thought of as being connected? Thus simplifying any circuit with multiple 0V reference points to only one 0V reference point?

Question: What is the point of doing this? Is it just to reduce the complexity of circuit diagrams later on? Because right now it definitely complicates the one below.

Yes and it really cleans up a circuit, removes a load of wires and makes all the ground points instantly visible without having to trace "wires".

Secondly, say instead of 0V reference points, those ground connections are actually earth ground connections.

English (as in UK / Ireland) practice is to use the word "earth" to signify a connection to the planet. Generally the earth symbol is used too.

simulate this circuit – Schematic created using CircuitLab

Figure 1. (a) Ground. (b) Alternative symbol. (c) Chassis. (d) Earth.

The reason why current would instead flow to the negative terminal of the battery is because it's more attracted to that then the neutral ground.

No. It's because current always flows in a loop. It's a bit like a bicycle chain in that regard.

Does any minuscule amount of current leak to ground?

To leak to earth two connections would be required so that current could flow through the earth back to the circuit.

Also, in the same sense as before, can we think of each individual 'earth' ground in the right diagram as connected?

Yes. That's the point.

• +1 Though I might add those symbols really only apply to wiring diagrams not PCB schematics. You can show them on a PCB, but at some point the net needs to terminate at some connector to actually make that connection. Even if it's just a mounting hole. – Trevor_G Mar 5 '18 at 19:17
• That's true but there is no mention of PCBs in the question and OP seemed to be referring to Mother Earth as well as circuit GND. – Transistor Mar 5 '18 at 19:30
• Thank you for the response! You mentioned current flows in a loop much like a bicycle chain loops, however what's the intuition behind that other than positive charge is attracted to the negative terminal? – Whisperrrr Mar 5 '18 at 19:32
• Yup, that's the issue with the name "ground". New folks have a hard time separating the two in their heads. – Trevor_G Mar 5 '18 at 19:34
• @Whisperrrr: The chemical energy creates the potential or voltage difference between the terminals. If there is a path - even with some resistance in it - the potential difference will push the current around the circuit. – Transistor Mar 5 '18 at 20:58

you could also have this equivalent schematic diagram

simulate this circuit – Schematic created using CircuitLab

So if I had 50 more 0V reference points, throughout some complicated circuit, all of them can be thought of as being connected? Thus simplifying any circuit with multiple 0V reference points to only one 0V reference point?

Yes. The ground symbol is simply a label that identifies a wire, or more accurately NET. It happens to be the net that you are using as your measurement reference, so for that reason it is given that special symbol.

Just like any other net label, wherever you see the same label attached to some other drawn line, the nets are connected, or more accurately, they are the same net.

It makes no difference if it is the ground symbol, or a net named "FRED".

simulate this circuit – Schematic created using CircuitLab

The only difference between the above two schematics, is in the right one, if I asked you for the voltage at the top of the diode, you would ask me.. "With respect to where?". Or, at least, you should.

See this answer for a more detailed explanation.

Further, showing the "ground" symbol in no way implies the net is connected to any kind of earth ground. It may be, but there is no way to tell from the schematic.

"Ground" is actually a misleading name. "Common" or "Reference" might be much less confusing to the uninitiated.

• Beside being a name abbrev. FRED is also a flashing rear-end device – Sunnyskyguy EE75 Mar 5 '18 at 19:35
• lol @TonyStewart.EEsince'75 TMI. – Trevor_G Mar 5 '18 at 19:37
• @TonyStewart.EEsince'75 I also coined FRED as the "Fault Recognition and Elementary Diagnostics" system in a hard drive product I helped develop that you are probably familiar with... The "Quail"... Though that was more of a dead duck... – Trevor_G Mar 5 '18 at 19:39
• Cool yes it was doomed from the start. I showed Walter Turchyn the servo on Maxtor with its R2D2 sounding voice coil on servo recal, it had a perfect acceleration, velocity and arrival position error signal just like the Quail was supposed to do but, sadly not. There were just too many well defined problems and too few solutions. fortunately I didn't waste any time on that project that cost a few hundred million $– Sunnyskyguy EE75 Mar 5 '18 at 19:47 • Yes I got to visit every HDD factory and had S/N #7 from Maxtor's single board 5.25" drive. Then got Sr. job offers later from Seagate and Micropolis, but the other half didn't want to move to the land of fruits and nuts. Just the same I enjoyed that part of my career in Cali. I had dozens of 50k$ testers to play with then a dept. to direct and to think I was clueless about rotating memory when I started. – Sunnyskyguy EE75 Mar 5 '18 at 20:14