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How Do Electrical Panels Work?

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A row of fuses

A row of fuses

Before Circuit Breakers, There Were Fuses

Before circuit breakers, mankind had fuses. They are single-use current interrupters with a component that melts if the current traveling through a circuit grows to excessive levels; thus, the fuse is used up and the electrical circuit remains protected and intact.

So, what do fuses do exactly? Well, fuses are usually just thin pieces of wire enclosed in heat-resistant glass or some other type of material. These fuses are plugged into the circuit and act as a conduit for the electricity flowing through it. You can think of fuses as a bridge that allows current to travel across the circuit. The wire (or other component) in the fuse is designed to tolerate a certain level of current. When the current flowing through the circuit experiences a surge, the wire melts or disintegrates, creating a gap that the current cannot cross. Going back to the bridge metaphor, the bridge has a weight limit. A surge of current is like a really heavy truck that caused the bridge to collapse. Don’t worry. The truck was empty, as was the bridge.

But, much like that bridge, the fuse needs to be replaced; once melted, the wire cannot repair itself. But fuses are cheap and plentiful, which is why people continue to use them. They continue to play a significant role in the electrical systems of cars, trucks, boats, or what have you. They work much the same way as they would in your home. Fuses in a vehicle allow an electrical failure in one system to keep components in another part of the car untouched.

However, if you want protection from a surge without having to worry about buying yet another fuse, you can always look into switches, relays, and circuit breakers, which is the focus of this article.

Fuses vs. Circuit Breakers

Circuit Breakers and Fuses Explanation

The Task and Duty of a Circuit Breaker

Circuit breakers are reusable versions of the fuse discussed above and are designed to be the weakest link in the electrical system chain. Circuit breakers prevent fires by creating gaps in the circuit if the temperature rises above safe levels.

Power is delivered from a source to your house’s large circuit that feeds smaller circuits. Think of the power source as a large rain cloud. This rain cloud pours and pours until it saturates the soil beneath your feet. Your house is a tree being nourished by the rainwater and its branches are the smaller circuits. Each of these circuits has two main components: the hot wire and the ground, or neutral wire. The hot wire is connected the power source and should be left alone. The ground is connected to the earth beneath your home and leads loose current into the ground.

These two wires never touch directly and so, the current has to pass through a load, which is the resistor. Most modern appliances and loads are manufactured with components that limit the amount of current allowed to flow through. In the United States, power is delivered at about 120 or 240 volts, but current and resistance vary from home to home due to different load capacities and requirements. But since voltage is constant, occasionally, something happens, something either random or just unfortunate. This something causes the hot wire to connect directly to the ground; with such little resistance a tsunami-like surge of current is fed through the wire, causing a fire.

Types of Circuit Breakers

  • Single Pole Breakers: 120 volts with ratings of 15-20 amps. The most common breaker in a home.
  • Double Pole Breakers: 240 volts with ratings of 15-50 amps. These often are found serving large appliances, including ovens and dishwashers.
  • Ground Fault Circuit Interrupter (GFCI) Breakers: Protects an entire circuit, limiting the usefulness of GFCI outlets. These are typically used on circuits where a fatal shock is very real possibility, such as bathrooms. GFCIs stop current flow in milliseconds when detecting a ground fault condition. Through constant monitoring of the current in a circuit's neutral wire and hot wire, these breakers don’t have to wait for temperatures to climb to unsafe levels.
  • Arc fault circuit interrupters (AFCI): Designed to shut down power to a circuit when they detect arcs of electricity caused by worn or damaged wires. AFCIs are used to protect circuits in bedrooms and common areas.
Various types of circuit breakers

Various types of circuit breakers

A modern, if messy, electrical panel

A modern, if messy, electrical panel

A few images of different types of electrical panels.

A few images of different types of electrical panels.

The Electrical Panel

The circuit breaker is an important device in the modern home, and one of the most important safety precautions you can take in your home. Whenever electrical wiring in a building has too much current flowing through it, these wonders cut the power until the problem is fixed. Absent circuit breakers, household electricity would be impractical; the potential for fires would be too great.

All these circuits feed into a central circuit breaker panel, or the electrical panel. This panel is usually in the basement or some dinky closet and includes an even number of circuit breaker switches, controlling various circuits in the house; these circuits might feed one large appliance or several outlets. Power is turned on and off at the electrical service panel.

Typically, one of these panels feeds the entire house but you may find yourself confronted with a "sub-panel" to serve an addition or some other specific area. 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 see a large double pole circuit breaker at the top of the panel called the "Main", which controls all the power to the circuit breakers below it. The breaker panel should come with a neutral bus and a grounding bar. The enclosure is sealed off by a panel and features a panel access door that allows you to access the breakers without removing the cover.

How to Add Circuit Breakers

Parts of an Electrical Panel

Electricity comes into your home through wires that connect to your breaker panel. Understanding the components in a panel can help you make an informed decision when making your selection. A typical breaker panel consists of these primary components:

  • Main breaker: A large double-pole circuit breaker that limits the amount of external electricity to protect the circuits.
  • Circuit breakers: Stacked in the panel in row of 2 and display an ON/OFF switch.
  • Bus bars: Receive power from the two thick black wires that bring power in from the electrical meter and feed the circuits in the home.
  • Neutral bus: Connects to the main circuit’s neutral wire. The neutral bar provides the contact point for the white wires that return electricity back to the breaker panel after flowing through the black wires to power a device. Your home’s main grounding wire also connects to the neutral bar.
  • Grounding bus bar: Unites all ground wires from various circuits and connects them to itself. Connected to a grounding conductor, a metal enclosure and, in the case of main service panel, to the neutral bar.

Types of Electrical Panels

There are a few types of electrical panels, each with their own codes requirement. Check with local authorities to determine which type of panel meets your local compliance requirements.

  • Main breaker panels: A built-in main breaker which can be used to shut off all power to your residence. Main breakers can be installed when the meter and feeder cable are within 10 ft. of the panel.
  • Main lug panels: Runs wires to lugs but requires a separate disconnect. The main breaker is located at the meter; if the main lug panel is used as a sub-panel, it will be connected to the breaker at the main panel. Separate disconnects at a meter help out firemen, who don’t have to enter the building to cut power.
  • Sub-panels: Separate breaker panels containing new circuits. These come in handy when a breaker panel doesn’t have enough slots to add new circuits. A sub-panel is also ideal for situations where multiple circuits are needed in a single separate area, like a workshop or greenhouse. Sub-panels allow more power to come through, but do not increase the total power being fed into your home.
  • Transfer Switches: A type of sub-panel that transfers portable generator power into electrical power through your breaker panel. If you live in an area where storms are common, you may have a permanent back-up power generator that uses an alternative power source, like propane or natural gas. The generator can be wired directly to the household breaker panel, providing a seamless switch from utility service to back-up power when the electricity goes out. Some generators come with a transfer switch that carries the same rating as the home’s main breaker panel.

There are two models of transfer switches:

  • Automatic: A larger initial investment but provide continuous protection for homeowners.
  • Manual: Less expensive but require a generator and manually switching the load to the back-up system.

For the Homeowner

The National Electric Code requires a minimum 100-amp service for a new home. Older homes are equipped with 60-amp services. If you want to replace a panel, match the current amp service on the old one or upgrade if you anticipate high power requirements.

If you have a much larger home with many more appliances, a good choice would be to install a 200-amp circuit breaker panel. If you are unsure what size you will need, you can calculate by looking at the name plate rating of each of the appliances you intend to install. Call a professional electrician to help you estimate the load requirements for your home.

Time to Test Your Knowledge!

For each question, choose the best answer. The answer key is below.

  1. What do you call the large double-pole circuit breaker that limits the amount of external electricity?
    • Bus bar
    • Main breaker
    • Circuit breaker
  2. What kind of circuit breaker shuts down power if it detect arcs of electricity caused by worn/damaged wires?
    • Single pole breakers
    • Ground fault circuit interrupter
    • Arc fault circuit interrupter

Answer Key

  1. Bus bar
  2. Single pole breakers

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.


Michael Corlette on April 01, 2019:

Love your article