Dryer outlets come in two basic types, three-prong and four-prong. Homes built after 2000 are required to have the four-prong outlet to comply with the National Electric Code. That same code forbids changing the outlet to a three prong, but customers may opt to change the dryer cord.
The three-prong outlets are found in older homes. Three-prong outlets provide 30-amp, 240-volt power. The corresponding plugs have the ground wire and the neutral wire joined together. Two prongs are straight, placed diagonally on the top of the plug. The third, which is the neutral prong, is L-shaped and on the bottom.
The four-prong outlets, known as 14-30 outlets, also deliver 240-volt power. The dryer plug has two live prongs on the left and right, the L-shaped neutral cord on the top and a half-round ground prong on the bottom. Like the three-prong version, the four-prong can only be plugged in one way.
Most dryer manufacturers sell their appliances without a cord, letting the user choose the correct type. A gas-powered dryer is sometimes the exception, usually having a three-prong plug. It only needs electricity to rotate the drum, not to heat the air. If plug installation is needed, it's easier to have it done at the appliance store.