Hi everyone. I am newbie in this forum and I have question which confuses my mind. Yesterday my teacher was explaining voltage sources in series and in parallel, and we did a problem in which ground was included. Teacher explained when the ground is positive and when it is negative but I did not understand it well. So, the question is when we consider the ground as positive and when negative? Thanks in advance

 

If there is only the single reference to earth ground, there should be zero current flow in the ground conductor, so polarity should make no difference?
If using DC it could be arbitrary whether +ve or -ve is used
Max.

 

The term "positive ground" and "negative ground" generally only have meaning in terms of which terminal of a battery-powered system is called "ground" (a better name is "circuit common"). So if the negative terminal of a battery is used as the common reference point, the circuit would be called a negative-ground system. If there are multiple voltage sources, then it becomes a matter of how the person describing the system chooses to describe it. Sometimes, in this case, there is one supply that is the primary supply and the others are there to power a few specific things. It is generally reasonable to use one terminal of the primary supply as the common. But, at the end of the day, you can throw a dart at the schematic and call the node closest to the point of impact the "common" and then all other node voltages are simply referred to it (i.e., saying that Node A is 10 V simply means that Node A is 10 V more positive than the common node).

 

I guess in this case the teacher was referring to CHASSIS Ground, if so the wrong symbol was used causing confusion.
Max.

 

I guess in this case the teacher was referring to CHASSIS Ground, if so the wrong symbol was used causing confusion.
Max.

I doubt they were even talking about a chassis ground. I think they were just talking about a circuit common reference point.

While it would certainly be preferred if the correct terminology were always used to distinguish these concepts, it will almost certainly never happen. The term "ground" will be used ubiquitously no matter how much we protest, so we have to be willing and able to extract the intended meaning from context. None of which is to say that it is not a worthy crusade to keep pointing out the proper terminology that should be used.