Ground vs. Ground?

[DocAmplify]

This is probably a really stupid question, but it's got me confused.   The circuit diagrams have grounds labelled, and these are typically the -ve or black wires that make their way back to the battery; correct?

There are also cases where the enclosure is referred to as a ground and is the third wire (green) from a three prong plug.  It seems that we're not supposed to connect the enclosure and the -ve terminals interchangeably.  Are they both really called ground?  Am I confused for no reason?

[therecordingart]

This is a really tough answer to articulate well, and one of the smarter folks here will answer it much better than I can.

When looking at a three prong 120v wall outlet in the US the small prong is hot, the large one is neutral, and the hole is earth ground. Earth ground and neutral connect at the circuit breaker box. Your conduit should be connected to earth ground for safety. That way if your hot comes loose and touches the conduit or your hot comes loose inside of your metal enclosure it will blow the breaker instead of electrifying the conduit or metal enclosure.  The neutral is also your 0v reference. If you measure voltage with your meter between ground and neutral you'll measure 0v. If you measure between ground/neutral and hot you'll measure the AC voltage coming in to the house.

Inside your stompbox "ground" is just a zero reference point. Your stompbox enclosure ends up connected to the negative terminal of the battery when you use non-isolated 1/4" jacks.

EDIT: My explanation sucks. I'm going to put together some stuff written better and post it later today.

Also,

-ve and ground MIGHT be used interchangeably, but -ve makes me think there may is a bipolar supply. In that case you'd have a 0v (ground) +ve and -ve. This can be obtained from putting two batteries or caps in series then using the point where they join as 0v (ground) and the negative side for -ve and the positive side for +ve.

[frank_p]

One is the ground, the other is the dead wire.  The dead wire can sometimes be connected to ground and sometimes: NOT.

This date to the time when the main wires were floating and there were no reference voltage where 0V=ground.  So there were no hot wire and no dead reference wire: between both wires there was always a Vac tension but it was whichever wire to the other.

The green or copper wire should always provide the shortest path possible to the true earth so that the metal case of equipment be connected to it.

Don't mess with main wires if you have no formation and certification.

[DocAmplify]

Thanks guys.  I'm starting to understand (a bit).  I'm much more comfortable with DC than AC though. 

As I read the forums I am constantly learning;  I see something that isn't relevant to me at the time but it partially sticks.  Then later, I learn something else and an old topic begins to make sense.

I'm working on the Tiny Giant project.  It uses a laptop adapter to get 15v and 4amps into my amp.  From the looks of it, I only have two leads; black and red (positive and negative DC leads). 

I see comments about a hum from the amp if ground isn't good.  At first I thought that meant getting the "green" wire grounded to the third prong of the AC outlet.  I can't even remember what thread it was in.  Hopefully my amp doesn't have the hum and I won't have to deal with it. 

[therecordingart]

Thanks guys.  I'm starting to understand (a bit).  I'm much more comfortable with DC than AC though. 

As I read the forums I am constantly learning;  I see something that isn't relevant to me at the time but it partially sticks.  Then later, I learn something else and an old topic begins to make sense.

I'm working on the Tiny Giant project.  It uses a laptop adapter to get 15v and 4amps into my amp.  From the looks of it, I only have two leads; black and red (positive and negative DC leads). 

I see comments about a hum from the amp if ground isn't good.  At first I thought that meant getting the "green" wire grounded to the third prong of the AC outlet.  I can't even remember what thread it was in.  Hopefully my amp doesn't have the hum and I won't have to deal with it. 

Using a SMPS like a laptop supply can be a little hairy with audio circuits. There can be noise issues unrelated to ground.