Three-phase power, or polyphase power is indeed distributed from the power company with three hot wires (with voltages 120 degrees out of phase) and a smaller, neutral wire, which is the ground.

Assuming a "balanced" load, the instantaneous power delivered to the load is constant in time, as opposed to pulsating with a single-phase power source. This is one of the attractions of three-phase power.

The typical three-phase power connections are the wye and the delta connections. These are the two "canonical" balanced connections that you often see in textbooks.

The wye connection is shown below. A, B and C represent the three hot lines and n the neutral. The phase voltage between each of A, B and C and the neutral is Vp, each 120 degrees out of phase from the others. The line voltage Vl, the voltage between two hot wires, is 3^(.5)*Vp.
```
_____
|     |
A   --------------|  Z  |---
|_____|  |
|
_____   |
|     |  |
B   --------------|  Z  |--|
|_____|  |
|
_____   |
|     |  |
C   --------------|  Z  |--|
|_____|  |
|
|
n   ------------------------
```

It turns out that if each of the loads Z are identical, no current flows on the neutral wire at all. This is called a balanced load. Therefore, the neutral wire may be totally omitted. Balanced loads are not usually the case in the real world of course, and a small amount of current flows along the neutral wire. This is why it is present (but smaller).

The delta connection is shown below. A, B and C represent the three hot lines. Note that the neutral is not included here, as it is unneccesarry.

```

A   ---------------------------|
|         |
__|__       |
|     |      |
|  Z  |      |
|_____|      |
|       __|__
|      |     |
B   -----------------|      |  Z  |
|      |_____|
__|__       |
|     |      |
|  Z  |      |
|_____|      |
|         |
|         |
C   ---------------------------|

```
There exist wye-delta and delta-wye transformations to represent one type of load in terms of the other. The voltage sources, which were not shown here, may themselves be connected to the load in either a wye or a delta configuration.

Most industrial three-phase voltage supplies are either 480 volts or 277 volts RMS, compared to 120 volts for residential usage. There are many three-phase applications where the ground wire is needed, and some, such as three-phsae motors, where it is not. You will find a mixture of these in the industry.