The Heart of Your Household Power System
Power is a lot like the air we breathe. It’s there, meeting our every need, constantly.
Power lines run along the street and extend to the main service panelboard, also known as a breaker box or fuse box. Electricity flows through two large wires, called hot wires, to the breaker box and then out on circuits to light fixtures or appliances.
How It Works
Power comes into your home through a line connected to an electric meter. This meter records the amount of electricity used and lets the utility company charge you for it. It’s important to note that the meter and all equipment up to it are the responsibility of the power company.
There are two 120-volt wires and one neutral wire connecting the meter to your house. A flaw in any of these wires could cause a problem with your household power system.
Once the power reaches the meter, it goes through a step-down process at switching stations, reducing it to about 115,000 volts. It then travels across miles of power lines to reach a distribution transformer. The next step down is another transformer, which reduces the voltage to about 240 volts. The final step down is at your home’s circuit breaker panel. Also known as a fuse box or service panel, this piece of equipment is your household power system’s gateway to your homes appliances and equipment.
Wiring
Electrical wiring is the conduit that delivers power throughout your home. Most homes have nonmetallic (NM) wire, which consists of two or more current-carrying conductors housed in plastic sheaths. The wires connect to screw terminals called lugs at your service panel, which is located near the electric meter.
The breaker box distributes electricity to circuits that run through your home, typically including lighting, ceiling fan and receptacle (or outlet) circuits. Each circuit includes a hot wire that Household Power System supplies electricity to outlets and a neutral wire that returns it to the service panel.
The hot wires are usually black, although they can be red or even white. Contact with a live wire is dangerous because it can cause a shock. The neutral wires are usually white, and touching them won’t hurt you unless there is no current flowing through the circuit. The neutral wires also have a grounding wire that diverts electricity to the earth in case of an overloaded or short-circuited circuit.
Circuits
Power arrives at your home from the electric utility, via a transformer that steps the voltage down to 120/240 V. From there, it runs over miles of wire to reach your power meter and main panel.
The hot wire (identified by its black casing) carries electricity to outlets and switches. Always touch a hot wire only when no electricity is flowing through it; doing so can cause wiring to overheat and catch fire.
The fuses or circuit breakers inside your house monitor current flow and protect against overheating, short circuits and overloading. They also detect faulty ground connections, which can cause shocks. Residual-current devices, such as ground-fault circuit interrupters and appliance leakage current interrupters, are designed to prevent appliances from drawing more current than the line and neutral wires can handle, which could also cause overheating and fire. They are typically located at receptacles and switches, but may be built into a plug or switch.
Breakers
Known as a breaker panel, electrical service panel or fuse box, this is the next piece of equipment in line to distribute electricity throughout your house. Power comes in here from the main line, which is usually 120 or 240 volts. Breakers connect to it and then to the wires that carry power to each circuit.
Each switch in a breaker panel has a number on it that corresponds to the circuit it controls. When the switch is set to OFF, power won’t enter that circuit.
Circuit breakers are designed to shut off the flow of electric charge if they detect an overload. They’re a great improvement over fuse boxes, which only work once and can’t be reset after blowing.
Subpanels
The main breaker panel is the heart of the house electrical system, but smaller panels known as subpanels help run new circuits for rooms or appliances. Each has four to 24 slots and is fed by a feeder breaker in the main panel.
The basic structure of a subpanel is the same as a service panel, with the primary feeder wire leading into ground bus bars and then into circuit breakers. Branch wire circuits then lead from the breaker into different parts of the house.
Many people choose to install a subpanel when they add a room to their home or work on a project like building an addition, remodeling the garage, or adding new lighting and fixtures. It helps keep the main panel from being overcrowded, and it makes it easier to reset circuits that might trip when working with power tools or other high-amperage equipment.
Low-Voltage Systems
A low-voltage system is comprised of electrical equipment that uses 50 volts (V) or less of alternating current. This type of wiring is typically used for doorbells, garage door opener controls, heating and cooling thermostats, alarm system sensors and control systems and outdoor lighting.
In an AC circuit, electrons move back and forth. This type of energy travels through a wire because organized electron Household Power System movement in the hot wire causes electricity to flow to fixtures and back to the main panel.
Some homes have subpanels, which are a set of additional breakers that provide power to areas of the house with multiple circuits or major appliances. In addition, some buildings use low-voltage systems for fire alarms, access control and surveillance. These systems are much safer and easier to install, maintain and repair than high-voltage equipment and require fewer, more lenient electric safety codes. They also generate less heat, which saves energy and helps preserve backup batteries.
