The Household Power System
Every day, we use electricity to run lights, fans and receptacles. It’s important to understand how electricity gets into your house and distributed throughout it.
Energy enters your home through two service wires carrying 120 volts of power. It then moves through your breaker box and onto your circuits.
How Electricity Works
Electrons move through metal conductors, like copper wires, to generate electricity. Surrounding these electrons with insulators prevents them from moving freely, thus containing the electricity. It’s this contained electricity, called current, that powers our appliances and lights.
Electricity begins its journey to our homes at huge power generating stations that produce it from coal, natural gas, wind or water. These generating stations are connected to each other, creating what is called the power grid. This allows a centralized system to manage and distribute power to areas where it’s needed most, such as running air conditioners during hot weather.
The power line that enters your home passes through a meter to track how much electricity you use, then through your service panel, which is often located in the basement or utility area. This box houses the circuit breakers that control how much electricity is supplied to each of your switches and outlets. If a short or overload occurs, these breakers shut off the flow of electricity to that circuit. For safety reasons, you should turn off individual breakers before turning off the main breaker in your home’s service panel.
An electrical circuit is a closed loop that provides an electric current path to and from the power source and back again. A circuit may be made up of any number of active and passive components including wires, batteries, transistors, diodes, capacitors, inductors and resistors connected in either a series or a combination of series-parallel circuits.
The service panel, also called the breaker box or fuse box (in older houses with fuses), is the distribution center for electricity to the house. It contains a main switch that can shut off all power to the house and individual switches (circuit breakers) that control the current going to different circuits.
Power flows into the house from the meter through a set of strips of metal called hot bus bars. Wires connect the hot bus bars to a breaker or fuse Household Power System and then to branch circuits that supply power to outlets in the house, lights, ceiling fans and appliances. Whenever possible, wiring should be run inside of the walls rather than through the attic. This helps protect against fires and shocks.
The service panel is where all power from the utility company enters your home. It’s usually located near the electric meter. It contains circuit breakers that connect to line wires with other devices, outlets and switches in your house. It also contains a grounding bus bar to help prevent injuries from electric shock.
Power leaves your service panel through a hot conductor, which has black or red insulation, and returns to the service panel via a neutral wire. There’s also a grounding wire, which is bare or has green insulation. The grounding conductor provides a third path for electricity to return to its source, the earth.
Older homes may have fuses instead of circuit breakers in their service panels. If you have a fuse panel, it’s a good idea to have it replaced by a modern one. Modern panels are more reliable and provide more control over the way your household uses energy. They also include a disconnect switch, which allows you to cut off power from the main panel without entering your house.
The main breaker panel contains lever-operated switches that control and protect the circuits within your home. Each switch is rated for a maximum amperage load that it will safely handle, and is designed to ‘trip’ or shut itself off if the current exceeds this limit. This is done to prevent fires and electrical injuries in your home. It’s easy to prevent a breaker from tripping by keeping track of how many devices are drawing current on the same circuit and making sure that the total doesn’t exceed the safe limit.
Each of the individual breakers within your breaker box connects to one or two hot bus bars inside the service panel. Breakers for 120-volt circuits connect to one bus bar, while those that power 240-volt devices, like your laundry machines and electric heat, connect to both. Each breaker has an identifying label on it that tells you what area of the house it controls.
Older homes used fuses instead of breakers, but they perform the same function. If a breaker keeps tripping, it could be overloaded, and you’ll need to remove some devices from the circuit. Newer homes use a type of breaker called an arc fault circuit interrupter (AFCI), which electronically monitors current to detect arcing, a common cause of household electrical fires.
Using a disconnect switch can help you prevent circuit overload. The switch allows you to isolate one section of a circuit from another, making it safe for service and repair work to be completed in that area without disrupting the flow of power to the rest of the system.
This type of switch is used on electric motors such as those in industrial forklifts, agricultural vehicles and aircraft tow tractors as well as Household Power System appliances like heaters and air conditioners. They ensure contractors working on the appliance don’t receive a dangerous shock from incoming power by shutting off the current.
These switches are available in two varieties: fusible and non-fusible. Differences include the switch’s current rating, operating voltage and short-circuit interrupt capacity. Other specifications include the number of poles (single or double) and the mounting type. For example, some switches are designed to fit into a panel cutout while others are built for a DIN rail. Fusible disconnect switches feature a fuse inside the switch box that blows when it senses an overflow of current.