01 of 09
The Electrical Service Panel (or Load Center)
With any electrical repair in your home you will have to turn the power off to the circuit serving your work. This is where you turn power on and off, at the electrical service panel which is more technically called a load center. The panel is what distributes electrical current to the various circuits within your home.
In this tutorial we will take a look at the service panel / load center and its components.Continue to 2 of 9 below.
02 of 09
Inside the Panel Door
With the panel door open, you can access all the circuit breakers or fuses in the panel. Typically, one of these panels feeds the entire house but you may have a situation where there is another "sub-panel" to serve a specific area such as an addition or new kitchen.
The circuit breakers are stacked in the panel and are controlled with a lever that places it in the "On" or "Off" position. You'll also see a large double pole circuit breaker at the top of the panel called the... "Main". It controls all the power to the circuit breakers below it.
Often there are stickers to be placed next to each breaker or a sheet adhered to the inside of the panel door that has space to identify the circuit served by a particular circuit breaker.
With a service panel having a fuse box, you'll have a number of screw in fuses instead of circuit breakers but the function of the electrical service panel is the same.Continue to 3 of 9 below.
03 of 09
Inside the Load Center
The electrical load center cover is typically held in place with 4 screws, one in each corner. Once removed you can see and access all components of the panel. You only need to do this when you're adding a circuit or replacing a circuit breaker but let's take a look around.Continue to 4 of 9 below.
04 of 09
The Main Circuit Breaker
Power comes directly from the electrical company's power line, through the electrical meter on the outside of your house and into the electrical service panel. The "Main" circuit breaker is often called a "Double Pole Service Disconnect" and is what controls the live power from energizing the circuits in the electrical panel. It's easily recognizable as it has two thick black wires feeding it from the electrical meter and consists of two circuit breaker handles joined... together. The Main is used to power all the circuits on or off at one time.
The Main circuit breaker also identifies the amperage capacity of the electrical panel and will have a number on it identifying its amp capacity such as "100" or "150". 100 amp service is the minimum allowed by code today, with 150 amp being very common. Electrical panels are also available in 200 amp and 400 amp sizes.Continue to 5 of 9 below.
05 of 09
Hot Bus Bars
The two thick black hot service wires feeding the Main each carry 120 volts from the electric meter and feed the two "Hot" electrical bus bars in the panel. These bus bars provide power to the circuits. By varying how many bus bars a circuit breaker connects to, that determines if it is providing 120 volt or 240 volt electricity to a circuit. Single pole circuit breakers provide 120 volts and connect to just one hot bus bar. Double pole circuit breakers provide 240 volts to a circuit and... plug into both hot bus bars. The electrical current leaves the service panel through the black power wire and is on its way to your electrical device.Continue to 6 of 9 below.
06 of 09
The Neutral Bar
Once the power leaves the electrical service panel through the black wire and does its work through the electrical device (light bulb, motor, etc.) the electrical current returns back to the service panel through the Neutral circuit white wire which is connected to the Neutral bar.
The Neutral bar is attached to the service panel and collects all the neutral white wires from the various circuits. The bar connects to the main circuit neutral wire where it returns the current back to the electric... utility company's transformer, usually the source of the electricity.Continue to 7 of 9 below.
07 of 09
The Neutral Bar and Ground Wire
The main house Grounding wire also connects to the Neutral bar thereby grounding the circuits to an earth ground directly via ground rods or by attachment to a metallic cold water pipe.Continue to 8 of 9 below.
08 of 09
The Ground Bar
The Grounding bar may be part of the Neutral bar or separate. In the photo above it is separate. It collects all the Ground wires from the various circuits and ties back into the Neutral bar.Continue to 9 of 9 below.
09 of 09
The Circuit Breaker
The circuit breaker is designed to be the weak link in your electrical system. But that's a good thing as it's designed to fail safely. When a circuit draws more current than it is designed to handle, the wiring gets hot and problems can occur including fires. That's why excessive current in a circuit is prevented by the use of "overcurrent" safety devices such as the circuit breaker. Circuit breakers connect to the Hot bus bars and come in a variety of types and capacities.
- Single Pole Breakers ...provide 120 volts and typically come in ratings of 15 amps to 20 amps. These breakers make up most of the breakers in your home.
- Double Pole Breakers provide 240 volts and come in ratings from 15 amps to 50 amps. These breakers usually serve dedicated circuits for large appliances such as electric dryers, stoves, air conditioners, etc.
- Ground Fault Circuit Interrupter (GFCI) Breakers protect an entire circuit from ground faults unlike the GFCI outlet which only protects at that location. With a GFCI Breaker you do not need local GFCI's. These are typically used on circuits where the likelihood of fatal shock is higher, such as bathrooms and can stop current flow within 25 milliseconds when detecting a ground fault condition.
Arc Fault Circuit Interrupter (AFCI) breakers are also available that have both GFCI and AFCI protection. An arc fault is a highly energized plasma discharge (similar to lightning) that jumps the air from an energized source (like your power panel) to a ground, like you. As the discharge happens it converts to extremely high heat and will melt insulation from wires. It can also start fires with surrounding combustible materials.