silly grounding question

[EETStudent]

I was thinking, I know the chassis is the ground source, but how does the chassis itself grounded?

[Paul P]

I was thinking, I know the chassis is the ground source, but how does the chassis itself grounded?

Through the third (green) wire in a three wire AC cable, one end of which is
bolted directly to the chassis and the other end goes directly to a building's
earth ground or, with a two wire AC cable, through the neutral (white) wire
to the breaker box which is then tied to the building's earth ground (spike in
the ground, water pipe, or similar).

The colours just mentioned are for North America.

Paul P

[Enzo]

We use the word "ground" too much and often improperly. The Euros call it "earth" and that maybe is a better term.

In the circuit we should call it "common." We can "ground" everything to the common in an amp, and the amp will work just fine with no connection to the earth ground. Look at vintage equipment that had only a 2-wire AC cord, or consider a battery powered amp. I would still use the term ground in describing connections inside the things, but in neither case was anything really grounded to earth. I shouldn't, but I do.

The chassis is usually the common in a guitar amp, you then may ground that common to the earth, generally by way of the third wire on the AC cord. The mains cord.

I have been using the term "mains" instead of AC in recent years, it tends to avoid confusion. I grew up calling the mains the "AC line" But in this world we have plenty of AC in the power supply secondaries, not to mention the signal path. And we also have lines, as in line out, line in, etc. So "AC line" is not specific enough to be unambiguous, so I try to use mains instead. No one thinks mains means anything other than the incoming power from the wall outlet.

[EETStudent]

So the green wire is the "earthing" source. I was just a bit confused, because I measured the AC between the black and the green and got 120. I was thinking I might get 0, but i guess if the green is 0 and the black is 120, i would the 120V difference on the meter