The standard voltage for electrical wiring systems in U.S. buildings is 240 volts. However, it is not simply a single wire feeding all that voltage in a single stream at 240 volts. Wiring systems are split so that there are two wires, each delivering 120 volts. These are used in a cyclic variation, giving what is known as an alternating current, or in tandem, to supply 240 volts to high-energy appliances such as tumble dryers.
U.S. wiring systems are comprised of three wires coming into the home, two "hot" wires and a neutral ground wire. The electrical current alternates between the hot wires, one being positive for electric flow while the other is negative, supplying most appliances with the 120 volts they need to function. When demand is higher, from appliances such as washing machines, both hot wires come into play and provide 2140 volts of power. The term alternating current also refers to how the electric charge flows in the wire. Sixty times a second it changes from zero to 120 volts, back to zero and to minus 120 volts.
To The Home
Electricity is generated by huge turbines in power stations. These turbines are fueled by fossil fuels such as coal and gas, nuclear energy or greener energies such as hydro or wind power. The resultant electricity has a very high voltage that enables it to be distributed over a network of power lines. Before the electricity is distributed into homes, it passes through a neighborhood sub station, where the voltage is lowered to the required 240 volts.
Electricity is a dangerous substance and The Consumer Product Safety Commission estimates that around 50 people are killed annually from accidental electrocutions involving wiring in the home. As such, home wiring systems have fuses or circuit breakers as a safety feature. Typically, a house will have a primary circuit breaker at the point where it receives electricity from the distribution network, which will trigger and stop the flow if the voltage is too high. Fuses perform the same function for different parts of the wiring system in the home and in appliance plugs.