Electronics notes/Ground
Yes, ground.
The basic concept so simple, the practical details both interesting, but also a conflated mess that means a lot of semi-experts (and smartarses like me) don't fully grasp.
And on larger scales things become more interesting - yet most of us deal with smaller scales, where other engineers have spent time making things simple and safe for you.
...yet even then you may care when you care about common mode noise, ground loops, and such.
Contents
Terms: Earth, ground, common, signal, chassis, shield, guard, virtual ground, etc.
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me) |
The main symbols are:
-
Chassis
- if the outside of a device is metal, that's this.
-
Signal common
- the reference used for a signal
- in PCBs there may be dedicated trace(s) (or not)
- in cabling this is often one of the wires in the cable
-
Earth
- classically a conductive pole hammered into the literal earth
However, people use 
loosely.
When only it appears in a circuit, it could refer to almost any concept mentioned around here.
When 
and/or 
are also present in the same circuit dagram, those specific distinctions are made, yet earth may sometimes still refer to any of the remaining. (Even when the physical design is very well considered (isolation, shielding, trace weight, order of connections, ground planes), the circuit diagram may not show each, as it may be considered a simplified functional summary.)
For a wider view, you want to know about the distinctions between the above and some further related concepts (most of which have no symbols):
- common current return path
- many components on a PCB that draw power tend to return it via a trace, often shared by many
- which we tend to call ground. This our main intuition in circuit design
- ...though it has no direct relation to earth (e.g. not all wired ones connect it to ground, no portable devices do)
- Even when this is connected to ground, it is not at quite the same potential, which becomes important in some cases with noise
- Safety ground/earth
- our main intuition around house wiring
- Ground plane
- in PCBs design: ground is often made as a large area of copper.
- This is a PCB design thing, and a nontrivial topic in itself, as it relates to coupling and more, and ends up being a balance of design considerations
- in antenna theory: a large surface, comparable to the relevant wavelength. Earth is an easy choice.
- itself a bit of a confusing one / misnomer.
- Also not often relevant to noise or safety discussions, because it's by nature internal to a circuit, so often there by design
- a subject in itself
- a strategy to alleviate some sorts of coupling
Earth/ground as in 'pole in the earth'
| This article/section is a stub — probably a pile of half-sorted notes, is not well-checked so may have incorrect bits. (Feel free to ignore, fix, or tell me) |
Earth can refer to a conductive pole hammered into the ground, near your house (usually near your breaker panel - seems to vary with a country's electrical code(verify)), connected via a chunky bit of wire.
Usually it isn't visibly exposed, but you almost certainly have one. (And usually exactly one - if you have multiple, your electrical code will probably say they must be connected to the main utility earth with a beefy cable, so there's usually not much point point to having more)
The earth in your wallplugs will be wired to that pole.
Also typically to a house's neutral, exactly once. It depends your country where that connection is. It may be at your power board, or that may be specifically disallowed and will happen at the transformer nearby. My guess is for practical reasons: corrosion of that ground pole will increase resistance and lower protection, and particular with underground wiring this is easier to deal with in one place rather than at every house(verify) - but this makes less difference around sparser housing, and around overground wiring
The main purpose of this pole is (mainly/only) to discharge static electricity, avoiding buildup of it.
That is, the earth rod is not necessary for safety grounding (of metal chassis via earthed wallsockets) to work - that works based on the circuit going through a trippable breaker (basically both wires go to the local transformer with thick enough wires), and this pole is not involved in that circuit.
For context: Safety grounding, residual current faults (see RCD), and static discharge are in effect three different protections -- that happen to share wiring, because it can, but only two of them use this pole.
Note that static discharge includes dealing with lightning. And then seemingly mainly lightning from outside(verify), in that the ground pole should be lower resistance than your house (there beinh very regular ground poles also implies lighting can never spread over the grid much(verify), which is nice design city-wise)
Earth/ground as in wallsocket wiring
Earth/ground as in the return path for current
Ground as in (not) making noise go elsewhere
On resistance of wires in sensitive signals
On sharing ground
Insulation faults and Protective Earth
Earthing as lightning protection
Residual-current breakers (and ground)
Other device safety
On floating and safety
More safety and/or noise stuff
"Ground loop"
See Ground loop
