Understanding how electricity works and how it is delivered from the street to the outlets in your home is the only way you can manage home wiring projects safely.
The most important thing to understand about electricity is that the typical amounts that flow through the wires in your home can be fatal under certain conditions if you come into direct contact with it. According to sources, up to 1,000 people are electrocuted in the United States each year. Furthermore, up to 500 people are killed in electrically caused fires.
Home wiring can be a very satisfying task for do-it-yourselfers, but if you don't know what you're doing or are in any way uneasy about working around electricity, don't try it. If you are unsure of whether or not you should do an electrical job, it’s always best to just call a professional electrician.
How Electricity Works
A home's electrical system is comparable to its plumbing system. Electrical current flows through wires in the same way that water does.
Both water and electricity flow. The main distinction is that you can see water (and touching water won't kill you). Water, like electricity, enters a fixture at high pressure and exits at low pressure.
Inside the pipes Both electricity and water enter the house, are distributed throughout it, perform their "work," and then leave.
Water first passes through the pressurised water supply system in plumbing. Current flows through hot wires first in electricity. Current flowing through hot wires is also pressurised. Voltage is the pressure of an electrical current.
Large supply pipes can transport more water than small pipes. Similarly, larger electrical wires can carry more current than smaller wires. Amperage is the capacity of wires to carry current.
Water is made available for use in a home via faucets, spigots, and showerheads.Receptacles, switches, and fixtures provide access to electricity.
Water eventually exits the house via a non-pressurized drain system. Electrical current also flows back through neutral wires. The current in neutral wires is not pressurised and thus has zero voltage.
An Electrical System
Large power plants generate the electricity that enters the home. Power plants are located throughout the country and generate electricity using turbines powered by water, wind, or steam.
Electricity from these plants is routed through large "step-up" transformers, which boost voltage to half a million volts or higher.
At these high voltages, electricity flows easily and travels through high-voltage transmission lines to communities hundreds of miles away from power plants. Substation-based "step-down" transformers then reduce the voltage for distribution along street lines. Smaller transformers on utility power poles further reduce the voltage to ordinary 120-volt current for household use.
Current lines to the house are either run underground or strung overhead and attached to a post known as a service mast. Most homes built after 1950 have three wires running to the service head: two 120-volt power lines and a grounded neutral wire. At the service panel, power from the two 120-volt lines can be combined to supply large 240-volt appliances such as clothes dryers or electric water heaters.
Incoming power is routed through an electric metre, which tracks power consumption. The power is then routed to the service panel, where it is distributed to circuits throughout the house. In the event of a short circuit or overload, the service panel also contains fuses or circuit breakers that cut power to the individual circuits. To prevent overloads, certain high-wattage appliances, such as microwave ovens, are usually plugged into their own separate circuits.
Elements of an Electrical System
Thousands of homes and businesses rely on power plants for electricity. Step-up transformers boost the voltage generated at the plant, allowing power to flow more easily along high-voltage transmission lines.
Substations are strategically placed near the communities they serve. A typical substation converts current from high-voltage transmission lines to low-voltage distribution lines.
Utility Pole Transformers
Utility pole transformers lower the high-voltage current that flows through power lines that run along neighbourhood streets. A utility pole transformer lowers the voltage from 10,000 volts to the standard 120-volt current used in homes.
Parts of an Electrical System
A modern electrical system consists of several parts. The following are the main components of how an electrical system is set up.
The Service Mast
The service mast is the metal post and weather-head that forms the electrical entry point into your home. The mast is powered by three 240-volt wires originating from the nearest transformer.
An Electric Meter
The electricity meter measures how much electricity is used. It is typically attached to the house's side and connects to the service mast. When power is applied, a thin metal disc inside the metre rotates. Your local power utility company owns the electric metre. Contact the power company if you suspect the metre is not working properly.
The Grounding Wire
A grounding wire connects the electrical system to the earth via a metal grounding rod driven next to the house, removing the risk of shock from equipment and metallic objects.
Electrical fixtures, such as light fixtures, connect directly to a home's electrical system. Wall switches are typically used to control them. Incandescent and fluorescent light fixtures are the two most common types of lighting.
Main Service Panel
Power is distributed to individual circuits by the main service panel, which takes the form of a fuse box or breaker box. Circuit breakers or fuses protect each circuit from short circuits and overloads. Fuses and circuit breakers are also used to turn off power to individual circuits while repairs are being performed.
Wire connections are protected by electrical boxes. All wire splices or connections must be contained entirely within a covered plastic or metal electrical box, according to the National Electrical Code.
Switches regulate the flow of electricity through hot circuit wires. Light fixtures, ceiling fans, appliances, and receptacles can all be controlled by switches.
Plug-in access to electrical power is provided by receptacles, also known as outlets. In wiring systems installed after 1965, the most common receptacle is a 120-volt, 15-amp receptacle with a grounding hole. Duplex receptacles are receptacles that have two plug-in locations.