10
\$\begingroup\$

I stumbled upon many terms for ground, naturally as newbie I got very confused.

  • ground earth
  • chassis ground
  • earth ground
  • common ground
  • signal ground

Are there any more?

I assume some are for AC and some for DC.

What is the difference?

many ground types and symbols

\$\endgroup\$
2

1 Answer 1

Reset to default
13
\$\begingroup\$

There are infinitely many ground symbols, as you can call anything ground. On some projects I have seen GNDA GNDB GNDC... etc.

A ground is a common reference voltage. No ground is truly 0 volts, but it can be considered close enough to be a common reference voltage. That is why we have so many grounds.

The difference is what they are connected to:

  • Earth and Earth ground - is connected in some way to earth potential: AC mains systems use it for fault currents.
  • Neutral - isn't a ground, it's a return current path for AC (but more often than not eventually connected to earth or another ground)
  • Analog and Digital ground: these are used in a project when a designer wants to split grounds to reduce noise in the design or for isolation
  • Chassis ground: usually connected to AC mains earth ground, and separate from PCB or power ground in a project; can carry fault currents.
  • Common ground: just your average every day ground. Usually labeled ground or GND.
  • Instrument ground: same as chassis grounds in most cases; another local ground for instruments.

At the end of the day ground is used for determining where currents go and what potential you want to reference the design from.

Here are some other terms about grounding typologies that are usually not marked in a symbol:

  • Ground loops: not really a symbol in most designs, just something to watch out for in connecting two systems' grounds together that are also connected to AC mains (or another ground). If you have ground connected through two different cables or earth grounds between two devices, it will make a magnetic loop that could create noise.

  • Star ground or multipoint: multiple grounds connected to one single ground.

  • Single point ground: grounds attached to a single ground with one wire in series; can be a problem for common mode noise from currents interacting with the resistance of the cable.

\$\endgroup\$
6
  • 2
    \$\begingroup\$ Nice anwer! What about to add "Single-point ground" in your list? \$\endgroup\$
    – PCBCrew Engineer
    Mar 2 at 16:53
  • 2
    \$\begingroup\$ ...and perhaps a Bond connection, found at the center of a star-ground structure, where all local grounds are connected together at one common location. This may, or may not include Earth, chassis, Neutral, and DC grounds. (one had better know what they're doing if a neutral is involved...) \$\endgroup\$
    – Chris Knudsen
    Mar 2 at 16:54
  • 1
    \$\begingroup\$ @PCBCrewEngineer Done, single point grounds usually aren't indicated on a design symbol but I gave it an honorable mention along with multi point. \$\endgroup\$
    – Voltage Spike ♦
    Mar 2 at 17:53
  • 1
    \$\begingroup\$ One comment on chassis ground. You said " usually connected to AC mains earth ground". This is a bit restrictive. A more accurate, at least IMM, description would be to say "connected to the primary input power's reference". In avionic & satellite systems, this may be a structural frame that the negative side of the 28 V or other DC power source is tied to. \$\endgroup\$
    – SteveSh
    Mar 2 at 20:28
  • 1
    \$\begingroup\$ You might also add "virtual ground". en.wikipedia.org/wiki/Virtual_ground \$\endgroup\$
    – PStechPaul
    Mar 3 at 0:41

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.