The Nature of Electricity
Most homes have two incoming voltages: 120 volts for lighting and appliance circuits and 240 volts for larger air conditioning and electric dryer circuits.
When an appliance switch is turned on, electrical current flows through the wire, completing the electrical "circuit" and causing the appliance to operate. The amount of flowing current is called "amperage." Most lighting circuits in the home are 15 amp circuits. Most electric dryers and air conditioners require larger 30 amp circuits.
The amount of electrical power needed to make an appliance operate is called "wattage" and is a function of the amount of current flowing through the wire (amperage), and the pressure in the system (voltage).
Mathematically speaking, volts x amps = watts. So, if we have a 120 volt system and a 15 amp current, we can flow a maximum of 120 x 15 or 1,800 watts on a typical lighting or appliance circuit. When too many lights or appliances are attached to the electrical system, it will overload and overheat. This can cause the wire insulation to melt and ignite, resulting in an electrical fire. The amount of electrical current flowing through wire is affected by resistance. This is known as "ohms." Resistance causes increased heat in the wire. Heat is the byproduct that makes some appliances work, such as an iron, toaster, stove or furnace. Large current faces high resistance when moving through a small wire. This generates lots of heat. That's how an incandescent light bulb works. Resistance through the light filament causes it to heat up which gives off a bright light. Electrical resistance also is affected by the length of a wire. Operating an electrical hedge clipper with a long extension cord increases resistance and might cause the cord to overheat, melt or ignite. The same occurs if too many strands of Christmas lights are connected together.
The size of electrical wire is dependent upon the amount of current required to operate a particular appliance. Wiring to the air conditioner, electric stove and electric dryer is much larger to handle the increased voltage (240) volts) and amperage (30 amps). Wiring is covered with a protective material called "insulation."
Electrical circuits in homes are designed so that all components are compatible. The size of the wire, outlets and circuit breakers are designed for an anticipated electrical load. A circuit is said to be overloaded when too much current flows causing heat build up or wiring to break down. When two bare wires touch, a "short circuit" is said to occur. This can lead to sparks and fire. Deteriorated insulation is one of the most frequent causes of short circuits.
A "circuit breaker" or "fuse" is a safety device designed to prevent accidental overloading of electrical circuits. They are set at a specific amperage. When that amperage is exceeded, it trips and shuts off the flow of electricity, stopping the circuit from continued overheating. When a fuse or circuit breaker trips, it is important to find the cause and correct it. Often, people will just reset the breaker or put in larger fuse. NEVER USE OVERSIZED FUSES ON CIRCUIT BREAKERS. NEVER SUBSTITUTE A PENNY OR FOIL-WRAPPED FUSE. This could cause a fire!
Published with the generostiy of the Phoenix AZ Fire Department
Learn more about Electrical Safety at http://phoenix.gov/FIRE/elecfire.html