# Understand Ground

I am confused regarding the attached image due to lack of understanding of ground. It's a basic question i.e. "How do I setup ground in my bread-board." Tried finding it but the confusion prevails due to unavailability of a working setup image.

Occasionally (particularly in AC power distribution and some radio antenna systems) Ground really does mean "a connection to the earth", but in most electronics "ground" is just a name we give to the point in the circuit we wish to call "zero volts" - the place where we put the black meter lead when measuring voltages elsewhere in the circuit.

This "ground" might better be called "reference" or "common", but we seem to be stuck with the term "ground". This "ground" has no magic properties.

This "ground"/common/reference is very often the most negative terminal of the power supply, but could be the positive terminal (ECL logic is supposed to operate on -5.2 volts, with the positive terminal of the power supply being "ground"/common).

In many audio and op-amp circuits, "ground" is the mid-point of the power supply, so we have both positive and negative supplies.

Again, there is nothing special or magical about "ground" - it is just what we call Zero Volts.

• Good points about the alternate supply configurations. – KalleMP Mar 12 '16 at 7:53

Ground is just the part of the circuit that directly connects to the negative terminal of your power supply or battery. It's the line at the bottom of the schematic. There's not much significance to the "GND" symbol in this case. If you're using a solderless breadboard, usually you'll use the strips marked "-" for ground.

• Thanks @Willis ..But had there been any one of the two(no negative and only the ground or vice-versa) I would not even be asking this question. Having 2 lines :-one for ground and one for -ve foxes me. Is it that ground is mentioned for layman to understand that negative part of the battery means ground – trickyal Mar 12 '16 at 6:32
• The concept of ground can be hard to understand at first because it means two different things. One meaning is the point on the circuit we use a reference when measuring voltages. For simple circuits that's usually the negative terminal of the power supply. Anything directly connected to that is ground. The other meaning is actual physical ground, a literal connection to the earth. Most hobbyist circuits are not earth-grounded, so the "ground" symbol just means the negative power supply terminal. – Willis Blackburn Mar 12 '16 at 6:45
• Some bench power supplies have three terminals: positive, negative, and "ground," which is usually green. In this case, "ground" on the power supply is a literal connection to earth via your home wiring. The negative terminal just connects to the power supply's transformer, which, being a transformer, is not directly connected to your home wiring. But you connect your circuit's "ground" to the power supply negative terminal, not to the green "ground" terminal. – Willis Blackburn Mar 12 '16 at 6:47

I also once felt that the concept of GND to be confusing. In that schematic GND can actually be removed from it. The GND does not add anything or do anything at all, really. So to answer the question Where should I connect GND to? you shouldn't actually connect it to anything. No extra cable to or from anything to anything else.

A natural question to ask then is Why have that GND symbol at all?. In this schematic it simply shows the point which we consider to be the zero point. As you can see in the schematic the batteries or power supplies are connected in serial. In such a setup there are two common ways to place GND.

One way is to place it at the lowest voltage, in this case the negative terminal of the first/lowest battery/power supply, that makes us consider both batteries/power supplies essentielly as one battery/power supply from zero to 9 volts.

The second common way is to place GND in the middle of the two batteries/power supplies. That makes us consider the point between the batteries/power supplies as the zero volt point. Both the batteries/power supplies then is seen by us not as a supply from zero to 9 volts, but instead a supply from -4.5V to +4.5V!

Where we choose to place GND depends purely upon what makes most sense in the circuit at hand.

Another example. Here the ground i just changed between 3 positions. The positions of GND does not change anything. All what changes is the numbers:

Even more examples

Let's assume that you have the following circuit and you want to know the voltage at the point where it says ? V. A very important thing to understand is that question does not make sense. Because, voltage is a relational concept. There is never simply a voltage but rather a voltage between two points. A multimeter has two leads, one can't just use one of them, one must use both.

So, in order for it to make sense we must measure the voltage in relation to something. The following image makes more sense. We see here that the voltage is 1.5 V in relation to the negative terminal of the lowest battery.

Another notation that could be used for the exact same situation is this:

Depending upon what makes most sense in the circuit at hand (which is sort of another question), we can measure the voltage at the point in relation to some other point, for example the middle between the batteries or the positive terminal of the upmost battery:

I hope that makes it somewhat clearer what is meant with ground being the zero volt point in relation to which all other points in the system is measured against (unless something else is explicitly specified).