1
\$\begingroup\$

According to Paul Scherz in his Practical Electronics for Inventors, he mentions in Chapter 2, Theory, the following:

Typically, the earth, with its infinite charge-absorbing ability and net zero charge, acts as a good point for comparison. It is considered the $0-V$ reference point or ground point.

I thought that ground in any circuit was a point in the circuit with respect to which other voltages were measure. And it was literally the connection to the earth (for safety purposes in house wirings, etc.) that earth meant.

But the text suggests that I’m wrong.

I just want to know what is correct.

\$\endgroup\$
  • \$\begingroup\$ "Earth" and THE earth are uhhh...different. \$\endgroup\$ – DKNguyen Aug 30 at 14:08
  • \$\begingroup\$ Not always.. ;) \$\endgroup\$ – Dampmaskin Aug 30 at 14:10
  • \$\begingroup\$ "infinite charge-absorbing ability" -- that's funny! In reality, the Earth has a capacitance relative to the universe at large of just a few hundred microfarads. Hardly what I'd call "infinite"! \$\endgroup\$ – Dave Tweed Aug 30 at 17:55
3
\$\begingroup\$

In most electronics, the term "Ground" is widely mis-used to mean the point in the circuit we choose to call "Zero Volts", and use as a reference when measuring voltage elsewhere in the circuit. We use "Ground" in this sense in portable electronics, cars, and even aircraft, where there is obviously no connection to The Earth. We should really call this "Ground" Common or Reference, but this mis-use of "Ground" is so deeply entrenched in the industry that there is no hope of changing it.

In AC power wiring, and some radio antenna systems, "Ground" does really imply a connection to The Earth.

\$\endgroup\$
2
\$\begingroup\$

Different authors define terms differently. To a designer of wearable home entertainment systems, "ground" is just a conductor with a name on it. But to a power utility worker, or someone who installs and maintains wiring in buildings ("electrician" in the US and probably UK, but -- terms), "ground" ("earth" in the UK, I think) means a wire that comes from a rod that's pounded into the earth right outside the building.

\$\endgroup\$
1
\$\begingroup\$

typically is the important word here:

If totally free to choose, most engineers will define ground potential to be earth potential in a system with an earth connection.

It's not mandatory, though.

\$\endgroup\$
  • \$\begingroup\$ But then, you can't use a multimeter to measure the voltage by pitching one probe in the earth and touching one to a circuit point, can you? \$\endgroup\$ – Atom Aug 30 at 14:17
  • \$\begingroup\$ @Atom Depends what level of voltage and currents you are looking for. You get a similar issue trying to use a multimeter with an ESD mat. Plus the earth point is not usually local to you. \$\endgroup\$ – DKNguyen Aug 30 at 14:21

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