Since I have joined this group and others devoted to electronics and computers, I have noticed a lot of concern about grounds and ground connections. Far more then I ever worried about in over 45 years of professional electronic design, installation, modification, and maintenance/repair.
Some facts:
1. The concept of a ground in an electronic circuit (and SOME, not most electric circuits) is it is simply a convenient and MOSTLY ARBITRARY reference level from which the other Voltages in a circuit are measured. The most important word in my last sentence is "ARBITRARY". Consider a project made with wood, perhaps a simple box. The box has a
definite length, width, and height. But where is the ZERO point? At the top? At the bottom? Left? Right? Center? WHERE? In truth, there is no real, intrinsic zero point. The plans may have one that the artist choose, but he/she could have chosen any one of a number of others and the table would still look and work the same. It would still be the exact same size.
The exact same thing applies to electronic circuits. There may be Voltage differences between different points, but there is no intrinsic zero Voltage. Oh, you might define one as a point where the positive and negative charges are present in equal numbers, but just how are you going to find or, more importantly, MAKE that point in the real world. Does even the earth, as a whole, have the same numbers of + and - charges? I am not aware of anyone who has ever made such a measurement. And what about local differences? Many natural processes can produce an excess of one or the other.
From a practical point of view, you can not produce nor even measure the presence of a "true" point of zero charge.
2. There is a reason for the ground connection in the AC power outlets in building in most countries. And that reason is protection against dangers like fire and loss of human life. In other words, protection against shocks to people and dangerous currents that could melt the conductors in the buildings' walls, causing fires - which cold also cause loss of human life. The ground wire is connected to an "earth ground" (that's where the name "ground" comes from) and it provides a very dependable return path for any stray current that may exist in a circuit. So if a conductor should come into contact with the external, conductive shell of a device, then a heavy current will flow in that conductor and back to the pole transformer, which also is grounded. And this heavy current will act to quickly trip the fuse or circuit breaker, disconnecting that defective circuit from the power grid. No current means no shock and no melting wires that set the building on fire. In one word, SAFETY. And the ground connection is called a SAFETY ground.
That is the purpose of the ground wire in a connection to the building's power grid, not any of your circuit design goals. And, from years, decades of working with video and audio circuits, I can personally attest to the FACT that those power circuit grounds are really poor at helping any circuit problems.
3. "Wall Wart" style power supplies, for the most part, do not connect to the SAFETY ground in the buildings' power connections. WHY? Because the industry, which is in a never ending search for less expensive ways of doing things, has lobbied for an alternative to that method of keeping the users safe from shock and fire. This is called double insulation and current limiting. The wall wart power supplies incorporate both of these technologies and, even together, they cost less than having a third, ground conductor. They have at least two layers of insulation that can each ensure against shock. The outer, plastic case is one of those insulation layers and something on the inside is the second, probably the varnish insulation on the transformer wire or an insulated circuit board or something that the inspection/certification body accepted. Current limiting is provided by something like a simple fuse or current limiting wire. Door bell transformers have had such inexpensive devices for many decades now. And since that is less expensive than the extra copper conductor, that is how it is done. Next time you look for a lower price, blame yourself.
So the "wall wart" style power supplies are an exception to the need for a SAFETY ground connection in most countries.
4. MOST electronic circuits do not really need a real "earth" ground. Things like modern automobiles and other vehicles have all manner of electronic and computer circuits in them and yet they are separated from the actual earth by four rubber tires. And if that is not enough, those tires usually roll on asphalt or concrete road surfaces, both pretty good insulators. Those cars are not grounded. Yet they work. Airplanes are another example. They also have tons of electronics and can be miles/km up in the air. No "ground" wires hang from their tails. Yet they work. The simple fact is, an actual "earth" ground is not really needed and, in most cases, can be omitted with NO DETRIMENTAL effects on the operation of the electronics in those devices.
Anyone who has worked in electronics for any amount of time knows this. Oh, sure there are cases where an earth ground is essential. An AM radio antenna is one such case. The "earth" ground forms a conductive mirror for the tower which is effectively only 1/2 of the actual antenna. AM broadcast frequencies being what they are (~1Mhz), that ground plane needs to extend for hundreds of feet (meters) from the base of the tower in all directions. But that need disappears with FM radio and higher carrier frequencies. Even pocket AM radio receivers do not need actual "earth" ground connections.
Most outdoor electronic devices are grounded for protection against lightning strikes, not for performance. And most indoor electronic devices do not need it at all except for safety considerations. And the wall wart power supplies take care of that need in other ways, as I have explained.
I wish I could somehow communicate this to all newbees in the electronic field. I am sure the "experts" here are going to come up with a million exceptional cases. But the real experts, who design our cars, planes, and so many other electronic devices, will know of what I speak. Newbees in electronics would be much better served by learning more about Ohms law. Seriously! It is far, FAR more useful than "earth" grounds.
In the words of the immortal bard, "Much Ado About Nothing."
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