The outlets that we see and use most often are for appliances that need 110 volts AC. Two of the openings in the outlet supply the voltage. The third connection (between the other two) is a grounding wire. This is a safety feature that works like a lightning arrester wire to keep electricity away from people who are using the appliances. Some heavy-duty appliances have high wattage heaters that operate at 220 volts.

STANDARD OUTLET SOCKETS