Basic Electrical Knowledge for Your Next Home Project

Electrical Service Connection and Meter

Your home's electricity starts with the power service and electric meter. The utility company's service cables (whether overhead or underground) extend to your house and connect to the utility's meter base. The electric meter plugs into this meter base. The meter measures the electricity your home uses and is the basis for the charges on your electric bill. The meter runs only when electricity is used in the house. This measurement is in kilowatt-hours.

Disconnect Switch

Some home electrical systems include a dedicated disconnect switch mounted on an outside home wall near the electric meter. In the event of a fire or flash flood, or if work needs to be done on the system, a disconnect switch allows you to shut off the power outside the property so you don't have to enter the building to turn off the power.

If an electrical system does not include a separate disconnect switch (and most do not), the main circuit breaker in the home's main service panel (breaker box) is the system disconnect.

Main Service Panel

After passing through the meter, your electrical service feeds into your home's main service panel, commonly known as the breaker box. Two large "hot" wires connect to big screw terminals, called lugs, inside the service panel, providing all the power to the panel. A third service wire, the neutral, connects to the neutral bus bar inside the panel.

In simple terms, electricity is supplied to the house on the hot wires. After it flows through the household system, it is fed back to the utility on the neutral wire, completing the electrical circuit.

Main Circuit Breaker

The service panel contains a large main breaker, the switch controlling the power to the rest of the circuit breakers inside the panel. It is sized according to your home's service capacity. A standard panel provides 200-amp (ampere) service. Older panels were sized for 150, 100, or fewer amps (amperes).

A main breaker of 200 amps will allow a maximum of 200 amps to flow through it without tripping. In a tripped state, no current will flow to the panel. The main breaker—in systems without an external disconnect switch—is the household disconnect.

Turning off the main breaker stops the power flow to all of the branch circuit breakers in the panel and, therefore, to all the circuits in the house. However, power always flows into the panel and to the service lugs even when the main breaker is shut off unless the power is shut off at a separate disconnect switch. Power is always present in the utility service lines and the electric meter unless the utility company shuts it off.

Branch Circuit Breakers

The breakers for the branch circuits fill the main breaker's panel (usually below). Each of these breakers is a switch that controls the flow of electricity to a branch circuit in the house. Turning off a breaker shuts off the power to all the devices and appliances on that circuit. If a circuit has a problem, such as an overload or a fault, the breaker automatically trips itself off.

The most common cause of a tripped breaker is a circuit overload. If you're running a high-demand appliance, such as a vacuum, toaster, or heater, and the power goes out, you've probably overloaded the circuit.

Move the appliance to a different circuit and reset the breaker by switching it to the "on" position. If the breaker trips again—without the appliance plugged in—you must call an electrician. There may be a dangerous fault situation in the circuit.

Devices

Devices are everything in the house connected to electricity, including switches, receptacles (outlets), light fixtures, and appliances. Devices are coupled to the individual branch circuits that start at the breakers in the main service panel.

A single circuit may contain multiple switches, receptacles, fixtures, and other devices or serve only a single appliance or receptacle. The latter is called a dedicated circuit.

Dedicated circuits are used for critical-use appliances, such as refrigerators, furnaces, water heaters, dishwashers, and microwaves. They can be shut off at the service panel without interrupting service to other devices. This also reduces the incidence of overloaded circuits.

Switches

Switches are the devices that turn on and off devices in your home. They come in many different styles and colors to suit your design needs. There are single-pole, three-way, four-way, and dimmer switches.

When you flip a switch off, it "opens" the circuit, meaning the circuit is broken or not complete, and the power is interrupted. When the switch is on, the circuit is "closed," and power flows beyond the switch to the light or another device it controls.

Outlets

Electrical outlets, technically called receptacles, provide power to plug-in devices and appliances. Televisions, lights, computers, freezers, vacuums, and toasters are all good examples of devices that can be plugged into an outlet.

Standard outlets in a home are either 15-amp or 20-amp; 20-amp outlets can provide more electricity without tripping a breaker. Special outlets for high-demand appliances, such as electric ranges and clothes dryers, may provide 30 to 50 or more amps of power.

Wiring in potentially wet home areas, such as kitchens, bathrooms, and laundry rooms, must have GFCI (ground-fault circuit-interrupter) protection provided by GFCI outlets or a GFCI breaker.

Wiring

Your home's wiring consists of a few types of wiring, including non-metallic cable (commonly called Romex), Bx cable, and wiring concealed in conduit. NM cable is the most common type of circuit wiring. It is suitable for use in dry, protected areas (inside stud walls, on the sides of joists, etc.) that are not subject to mechanical damage or excessive heat.

Bx cable, or armored cable, consists of wires running inside a flexible aluminum or steel sheath that is somewhat damage-resistant. It is commonly used where appliance wiring, such as dishwashers and garbage disposals, is exposed.

A conduit is a rigid metal or plastic tubing that protects individual insulated wires. It is used in garages, sheds, and outdoor applications where the wiring must be protected from exposure.

Wires inside NM cable, Bx cable, or conduit are sized according to each circuit's amperage. Wire size is given in its gauge number. The lower the gauge, the larger the wire, and the more current it can handle. For example, wiring for 20-amp circuits is 12-gauge, heavier than the 14-gauge wiring used for 15-amp circuits.