Whenever you need to perform electrical repairs in your house, it’s essential to cut off the power to the specific circuit you’ll be addressing, which you can do at the main electrical service panel. This panel is commonly referred to as the breaker box, although in professional terminology, it’s known as a load center.
The primary service panel functions as the central hub for the home’s electrical system. It takes in the electrical supply from the utility provider and channels it to the individual circuits that power the different lights, outlets, appliances, and other equipment in the residence. The main service panel allows for the control of all circuits, except for the incoming power from the utility.
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Behind the Door of the Panel
A service panel is a metal enclosure featuring a door that swings open or a panel that lifts up at the front. When the door is opened, it provides access to all the circuit breakers contained within. Usually, a single panel powers the entire residence, although there may be a secondary, smaller panel known as a subpanel. This subpanel is often utilized to supply power to a specific section, such as an extension, a spacious kitchen, or a separate garage. Functionally, a subpanel operates similarly to the main service panel, but it receives power from the main panel of the house instead of directly from the utility service.
Every circuit breaker is operated by a lever that can be manually adjusted to either the ON or OFF setting. When a circuit breaker trips—typically as a result of an overload or a circuit issue—the lever will automatically shift to a neutral position that is situated between ON and OFF. It is important for breakers to be clearly labeled to indicate the primary area or appliance that the circuit serves. These labels can be in the form of stickers or handwritten notes placed next to the breakers or on a sheet that is attached to the inside of the panel door.
Please be aware that older residences that haven’t undergone electrical service upgrades might still feature service panels equipped with fuses instead of the circuit breakers that have been the norm since the 1960s.
Within the Service Panel
Upon opening the panel door, you can reach the circuit breaker switches, which is sufficient for most homeowners. However, to install or replace a circuit breaker, you must take off the protective cover surrounding the switches, referred to as the dead front cover. This cover is usually secured with a screw located in each corner. Once the cover is removed, you can access all the panel’s components. Some panels feature a distinct door and cover, while others combine both into a single unit.
Caution: Prior to taking off the dead front cover, ensure that the main circuit breaker is turned off (refer to the following slide). This action will cut off power to all circuit breakers and household circuits, but it will not disconnect the power supplied by the utility. The utility service lines and the terminals inside the panel will still be energized (potentially carrying lethal electrical current) unless the utility provider disconnects the service to the residence.
Primary Circuit Breaker
The primary circuit breaker is a sizable switch typically found at the upper section of the panel, although it can occasionally be positioned at the lower end or along one of the sides. This breaker regulates the power supply to all the branch circuit breakers, which manage the individual circuits within the panel.
Electricity is supplied through utility service lines, passes through the external electrical meter of your home, and then enters the service panel. In certain setups, there may be an additional disconnect switch located between the meter and the panel. The main breaker is responsible for simultaneously turning the power to all branch circuits ON or OFF.
The primary circuit breaker indicates the overall amperage capacity of the service panel and is marked with a number that reflects its amp rating, such as 100, 150, or 200. Currently, the standard amperage for new panels is 200 amps, although some panels may offer even greater capacity.
Caution: The primary circuit breaker disconnects power from all branch circuits, but it does not cut off power from the utility source. The utility service lines and the terminals they connect to within the panel stay energized (carrying hazardous electrical current) unless the utility provider disconnects service to the residence.
High-Temperature Bus Bars
The two robust black service wires supplying the main circuit breaker each transmit 120 volts from the electric meter and connect to the two hot bus bars within the panel. Circuit breakers are designed to fit securely onto one or both bus bars to deliver power to the circuits. Single-pole circuit breakers deliver 120 volts and are linked to a single hot bus bar.
Double-pole circuit breakers deliver 240 volts to a circuit and connect to both hot bus bars. The electrical current exits the service panel via the hot wires linked to the circuit breakers. Single-pole breakers feature a single hot wire (typically black), whereas double-pole breakers consist of two hot wires, which can be black, red, white, or other colors.
Neutral Busbar
After the electricity exits the electrical service panel via the hot wire(s) of a circuit and powers various devices such as light bulbs and outlets, the electrical current makes its way back to the service panel through the neutral wire, typically colored white. This wire connects to the neutral bus bar, which in turn links to the main service neutral, allowing the current to return to the electric utility grid.
In numerous service panels, the neutral bus bar functions as the grounding bus bar as well, providing a termination point for the individual bare copper circuit ground wires. In such instances, it is commonly called a neutral/ground bus bar.
Primary Bonding Jumper
The primary bonding jumper establishes a grounding link between the neutral/ground bus and the service panel. Additionally, the grounding electrode conductor (GEC) serves as another grounding connection. This conductor, typically a bare copper wire, links the neutral/ground bus bar to a grounding rod that is installed in the ground close to the service panel, or to the metal rebar within the home’s foundation. This ultimate connection to the earth enables any stray electrical currents, like those generated by a lightning strike, to dissipate safely into the surrounding soil.
Earth Bus Bar
Certain service panels feature an independent bus bar designated for ground-wire connections, rather than a combined neutral/ground bus. In this scenario, the ground bus is electrically linked to the neutral bus solely in main service panelshowever, in subpanels, the ground bus and neutral bus remain unconnected.
Electrical Disconnect Switches
The circuit breaker serves as the vulnerable point in every electrical circuit. However, this is beneficial because it is engineered to fail in a safe manner. To protect against excessive current, overcurrent protection devices, including circuit breakers (or fuses in older systems), are utilized. Circuit breakers are linked to the hot bus bars and are available in a wide range of brands, types, and capacities.
- Single-pole circuit breakers deliver 120 volts and are usually rated at either 15 amps or 20 amps. They are designed to support the majority of the electrical circuits in a household.
- Double-pole circuit breakers deliver 240 volts and are available in amperage ratings ranging from 15 to 50 amps. Typically, these breakers are used for dedicated circuits that power large appliances, including electric dryers, ovens, and air conditioning units.
- Ground-fault circuit interrupters (GFCIs) safeguard entire electrical circuits against ground faults, thereby reducing the risk of electrical shock.
- Arc-fault circuit interrupter (AFCI) breakers safeguard an entire circuit against arc faults, reducing the risk of residential fires. Certain dual-purpose breakers can offer both GFCI and AFCI protection at the same time.
