Electronics notes/Ground

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See also Category:Electronics.

Yes, ground. The basic concept is simple, yet it's also a mess of conflation that means a lot of semi-experts (and smartasses like me) don't actually understand it.

Which doesn't matter much a lot of the time, particularly when engineers make things simple for you.

But you may care when you care about common mode noise, ground loops, and such.

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:

  • Earth.png Earth
clasically a conductive pole poking into the literal earth
practically any of these
  • Chassis.png Chassis
if the outside of a device is metal, that's this.
  • Signal common.png 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

Note that people use Earth.png loosely - when only it appears in a circuit, it could refer to almost any concept mentioned in this section.

When the chassis and/or signal common symbols are present, those specific distinctions are made, yet earth may still refer to any of the remaining.

(And 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.)

Further related concepts:

  • common current return path (for which there is no symbol).
many components that draw power tend to return it to a trace 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. no portable device connects it, and not all wired ones do)
Even when this is connected to ground, it is not at quite the same potential, which becomes important in some cases with noise

  • 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 between things
in antenna theory: a surface large, comparable to the relevant wavelength. Earth is an easy choice.

  • Safety ground/earth
our main intuition in house wiring

a subject in itself

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
  • Guarding
a strategy to alleviate some sorts of coupling

Earth/ground as in 'pole in the earth'

Earth can refer to a conductive pole in the earth near your front door.

Usually it isn't visibly exposed, but you have one. (And usually exactly one - if you have multiple, electrical code often says they must be connected to the main utility earth with a beefy cable, so there's usually little point to more) (One reason to have more is lightning rods, to ensure there is enough conductance for a strike(verify), but there are more significant footnotes to this, code-wise)

The main purpose of this pole is (only) to discharge static electricity, avoiding buildup of it.

Which includes dealing with lightning. Seemingly mainly lightning from outside(verify), because your house is a higher-resistance path than the ground pole in front of it. (this setup also implies lighting can never spread over the grid much, which is nice design city-wise)

Earth is not for safety grounding of chassis. that safety measure would work without the pole (because it's the job of the wallplug wiring and main breaker - see notes below).

It is however required to detect ground faults, e.g. with an RCD.

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

Safety discussions (mostly) related to ground

Grounded sockets supporting chassis safety
Earthing as lightning protection
Residual-current breakers (and ground)
Other device safety
On floating and safety

More safety and/or noise stuff

More terms: Floating things (and galvanic isolation)