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Inside Your Home’s Electrical Service Panel

Get essential knowledge about your home’s power distribution center.

Electrical Panel, Home, Fuse Box iStock

Major power outages are easy to understand: Your house loses electrical power when a storm or accident takes down the power lines, or when a utility crew needs to make repairs or alterations in your area.

But what about the many smaller power outages that can occur in your house—like when an appliance or power tool stops working, or when the recessed lights in a room suddenly go out? To solve the mystery behind these mini-outages, you need to take a look at the main electrical service panel in your house –the distribution center for all the electricity you consume. A little knowledge about this essential piece of electrical equipment can go a long way in terms of the safety and functionality of your home.

Service Panel Anatomy: A Big Box of Circuit Breakers

You’ve probably heard your main electrical service panel referred to by other names. In the old days, it was called a fuse box, because it contained all the main fuses for different electrical circuits throughout the house. But today, a service panel is often called a “breaker box,” because it’s full of circuit breakers, which are far superior to fuses in terms of safety and convenience.

The main service panel is typically located in the basement, or (in a house without a basement) in a utility room. Some homes will also have a sub-panel, which is a smaller version of the main panel, to control electrical circuits in a garage, a workshop, or other outbuilding. A service panel is easy to spot: It’s a gray steel box with a hinged door, securely attached to the wall at around shoulder height. Inside the box, you’ll find two rows of switches –the circuit breakers that can be toggled on and off to control the electricity used in different parts of your house.

Above the circuit breakers, there’s a larger main switch that controls all the power available to the house from your electric utility. This switch is sometimes referred to as the service disconnect. Behind the cover plate surrounding all the panel’s switches, you’ll find three large wires entering the box from the main power line, and a bunch of smaller wires that connect individual circuit breakers to electrical cables that run to different circuits throughout the house.

Know Your Breakers

Next to each circuit breaker (stamped into the steel cover panel), you’ll find a number, enabling you to match individual breakers to specific circuits by filling in the lined sheet of paper glued to the back of the panel door. For example typical circuit breaker labels might be: “Kitchen outlets,” “Living room lights,” “Clothes dryer,” etc. An average-size house is likely to have at least several lighting circuits, several receptacle (aka outlet) circuits, plus circuits that control major appliances like the furnace, clothes dryer, water heater, etc.

Circuit breakers are described by their amperage rating and by their type. But before delving into these distinctions, let’s look at their common functions. For starters, a circuit breaker is an electronic switch that enables you to manually deactivate (shut off) a circuit at the service panel. You’d need to do this if you were doing electrical wiring work that might put you in contact with live wires–jobs like replacing a ceiling fan, or installing a dimmer switch.

Another common characteristic: All circuit breakers are designed to turn off automatically when the electricity flowing through the circuit exceeds the breaker’s power rating. This can happen when too many devices are running on one circuit, like if you were using a heavy duty vacuum in the garage while someone else was also using a circular saw. By shutting down in response to high amperage draw, the breaker avoids overheated wiring that can cause an electrical fire and damage electrical equipment.

Circuit breakers that feed receptacles will be rated at 15 or 20amps; this means they will automatically trip if current exceeds these ratings. Lighting circuits are controlled by 15amp breakers. Your service panel will also contain a limited number of larger “double-pole” breakers that have higher amp ratings for big appliances like stoves and clothes dryers.

Additional Safety Features

There are two special types of circuit breakers that provide extra measures of safety. A circuit breaker designated as GFCI (Ground Fault Circuit Interrupter) will automatically trip when current leakage is detected. This is a safety hazard that can occur when electric wires get wet, so GFCI protection is required in kitchens, bathrooms, garages, basements, and other potentially wet areas. A breaker designated as an Arc Fault Circuit Interrupter (AFCI) will trip in response to overloading and sparks.

Circuit breakers do more than protect a home and its inhabitants from electrical hazards. They can also provide valuable diagnostic information. If a GFCI breaker controlling kitchen outlets keeps tripping, it indicates that current leakage is occurring somewhere in the circuit—a problem you’ll want to fix. It can also indicate a faulty circuit breaker, but this isn’t usually the case. If a standard circuit breaker is tripping, this indicates that one or more devices is drawing too much power from the circuit. When an AFCI breaker trips, it can be due to arcing (sparks) caused by loose or improper wiring.

It’s smart to get acquainted with your main service panel, and all the circuit breakers it contains. These super-sensitive switches keep you safe, and alert you to electrical problems that need attention.