3-Prong Dryer Outlet
The 3 prong wiring diagram above shows the proper connections for both ends of the circuit. This circuit originates from the breaker box containing a 2-pole 30 Amp breaker. This size breaker requires a minimum of a #10 gauge wire so this wire used would be a 10/2 with ground.
Now a 3-prong outlet is outdated from modern electrical codes but is accepted if you already have one in your home. If your running a new circuit, I highly recommend that you bring your outlet up to code and install a 4-prong dryer outlet. (See Below)
The difference between this diagram and the 4-prong outlet below is the addition of a neutral wire. The neutral line is a return line for the voltage and should not be done through the green ground wire, even though a neutral and ground are really the same, so new codes require a dedicated neutral line as well as a dedicated ground line. This just simply separates the ground circuit and neutral circuit versus having the ground line act as a neutral in the older circuit above.
Clear as mud right,
4-Prong Dryer Outlet
(Yellow Wire = White)
Some panel or breaker boxes will have a dedicated neutral bar and a dedicated ground bar, but they will still be physically connected.