Understanding the Household Power System

The power that runs your lights, appliances and electrical outlets comes from a power grid. This power travels to your home on large power lines, then reaches a substation where it is reduced to a lower voltage by power transformers.

This power then travels to your electric meter and service panel. Here, you’ll find the main disconnect switch that stops electricity flow during emergencies and repairs.

Electrical Wiring

Whether you’re looking to install or troubleshoot a household electrical system, knowing how current flows through your house helps you understand what might go wrong. Electricity enters your house through two 120-volt wires (or one 240-volt wire) from the power company and backs out through a ground-related neutral wire. For electricity to function properly, it must complete a circuit through the lines, the breaker panel and the circuits that supply devices like switches and outlets.

The wires carry alternating current that turns on and off 60 times per second. The current goes to and from the switch, outlet or appliance, and the metal contacts and other components in each. If a wire or other element fails, the current can stop moving through the circuit, causing damage to the device and possibly a fire.

Breakers or fuses in the panel shut off power to individual circuits if there’s a short or overload. The hot wires, which are black or red but never bare or white, connect to strips of metal called hot bus bars and are distributed through a series of breaker panels in your house.

A separate 120-volt circuit of wires serves each receptacle and switch in your house. Another, heavier wire, is dedicated to a dishwasher, garbage disposal or electric water heater, which use 240-volt current. Code requires each of these circuits to be separated from other circuits. Spliced wires are run into electrical boxes that are mounted in walls throughout your home. These are required by the National Electric Code to make it easy to access each splice, especially if you need to work on a repair.

Service Panel

Many problems in a home are caused by an outdated electrical service panel. Flickering lights, strange sounds Household Power System coming from the fuse box, breakers constantly tripping, and even smoke coming from outlets are signs that you need to upgrade your service panel.

The electrical service panel, also called the breaker panel or fuse box (in older homes with fuse-controlled circuits), is the distribution center for your house. It’s a large metal box with a hinged cover, typically located in the garage workshop or an out-of-the-way corner of the home. Inside the panel is a main switch that shuts down power to the house from the utility wire and individual switches (called circuit breakers) that control power to different parts of the house.

In most single-family houses, the utility wire connects to a service drop that runs to the service panel. The wires from the service panel then split off into exit wires that supply power to different areas of the house. The branch wires, as they’re called, are labeled with a combination of letters and numbers to identify the circuits they serve. For example, “UPS WEST” would indicate the upstairs west bedroom circuit.

You can look at the metal knock-outs on your service panel to see how many spaces are available for adding new circuit breakers. However, it’s best to have an electrician remove the cover and check for you.

Circuit Breakers

The main breaker panel is where power flows to outlets, lights, appliances and more in your home. There are a number of switches (often labeled by room) that monitor the flow of electricity to prevent overcurrent conditions. Overcurrent can damage equipment and even cause fires. Circuit breakers are designed to shut off power quickly to prevent this and other electrical hazards.

A single-pole breaker is the most common type of switch that monitors a household circuit’s 120 volts and controls all of your standard outlet receptacles. Twin or tandem breakers are two switches connected in the same box with different amperage ratings that control separate circuits. They are often used for devices that draw high voltage like furnaces, water heaters and EV charging stations in your home.

In addition to the regular breakers you’ll also have GFCI circuit breakers in your breaker box, which protect against ground faults in receptacles in bathrooms, kitchens and garages. Some breaker boxes may even contain AFCI breakers, which are specifically designed to protect against fires caused by electrical arcing in worn or damaged cords and wiring.

If one or more of your breakers trip on a regular basis, this is usually a sign that there is a problem somewhere in the circuits that they are controlling. It’s always a good idea to have your home’s electrical system professionally inspected by an electrician when this happens, as a faulty circuit breaker can easily lead to an electric shock or a fire.

Outlets

There are many different types of electrical outlets, also known as receptacles. These outlets allow you to plug in electric devices such as lamps, hair dryers and small appliances. The most common is the two-pronged receptacle, which provides 120-volt power to equipment plugged into it. Other options include three-prong receptacles, which have a grounding plug to reduce the risk of shock from metal handles and spouts on plumbing fixtures; and GFCI outlets, which are required by national wiring codes in damp locations such as bathrooms. Other special outlets have shutters to prevent unauthorized use; these are sometimes used for computer or TV outlets. A tamper-resistant outlet prevents the removal of a plug by an object larger than the socket; this Household Power System is often used in children’s rooms, where it is possible for young children to remove plastic outlet covers. Arc fault circuit interrupters (AFCIs) are designed to cut power to equipment when a faulty circuit within an outlet or one of its plugged-in items is detected. They can greatly reduce the number of electrical fires in homes.

It takes a lot of complex equipment to get electricity from the power plant to your bedroom light. Next time you walk down the street, or turn on a light in your home, think about all of that equipment and how it all works.