How Does a Circuit Breaker WorkA circuit breaker is a switch that protects your home and electrical system. When a circuit becomes unbalanced and begins drawing more electricity than it was designed to handle, the circuit breaker cuts power before the excess current overloads your internal wiring, melts the circuit, or causes a fire. But exactly how does a circuit breaker work? How does it monitor power flow and keep you safe?

Home Electrical Circuits

Before you can understand how a circuit breaker works, you have to understand your home’s electrical system. Though you may not realize it, the wires inside your walls form an extensive electrical grid. One set of wires (hot wires) brings power into your home and delivers it to your outlets and appliances. A second set (neutral wires) takes the power out of your home and delivers it back to its original power source, completing the circuit.

Nearly every room in your house is powered by a separate circuit, each with its own set of hot and neutral wires. These circuits are fed by service wires connected to your breaker box, which houses the circuit breakers and controls the flow of energy through your home.

Volts, Amps, and Watts

Circuit breakers trip and cut power whenever the current flowing through it exceeds its maximum amperage, otherwise known as its load capacity. Amps, volts, and watts are the fundamental units of electrical work. Amps measure electrical current, the number of electrons flowing through a circuit every second. Volts measure electromotive force, the pressure that makes electrons move through a circuit. And watts measure energy transfer, the total electrons used to power a circuit.

Amps, volts, and watts are interconnected. Multiplying amps and volts tells you how much electricity a device consumes. Dividing watts and amps shows you the electrical pressure inside the device. And dividing amps by watts tells you the speed of the electricity moving through it.

  • Volts x Amps = Watts
  • Watts / Amps = Volts
  • Watts / Volts = Amps

Even the best conductors resist electricity to some degree, which means every circuit has a maximum wattage (i.e. load) that it can carry. Consider a light bulb. Electricity flows through it the moment you switch it on. But because light filaments resist electricity, electrons flow in faster than they can flow out, creating an excess of energy that makes the filament glow.

However, if you plug a 10W bulb into a 50W socket, electrons build up so fast the filament overheats and incinerates. The same thing happens when you run 3,000 watts through a standard 2,400 watt outlet. The excess current overloads the wires and burns them out.

How Circuit Breakers Work

Circuit breakers are contained inside your breaker box, which is generally located in low-traffic areas, such as a basement or garage. They’re made from insulated plastic, with two terminals that conduct electricity from the service wires out into your home. All the energy that passes through the circuit breaker flows through two contact plates inside: a stationary plate and a moving plate.

The stationary plate is connected to the plastic frame, while the moving plate is connected to a metal arm called an actuator. As long as the plates are in contact, the circuit is complete. Whenever they’re apart, the circuit is broken. While the basic functionality is the same, there are two distinct types of circuit breakers: magnetic and soldered.

In magnetic circuits, the actuator is on a rotating pivot controlled by a magnet, charged by the current flowing through the circuit breaker. If the current is below the maximum load, the magnet never becomes strong enough to trip the actuator. However, if the current becomes excessive, the magnet pulls the moving plate away from the stationary plate, cutting the flow of electricity.

In soldered circuits, the actuator is controlled by a block of alloy (solder) made from two metals with different coefficients of thermal expansion (i.e. they expand at different temperatures). As the current flows through the actuator, it heats the solder. If the circuit exceeds its maximum load, the solder expands and bends, due to the difference in thermal coefficients, which turns the actuator and breaks the circuit.

Homeowners can reset tripped circuits after they cool down. However, to prevent them from tripping again, reduce the electrical load by disconnecting a few appliances first. If a breaker trips repeatedly, call an electrician. It may have a short circuit, ground fault, arc fault, or some other malfunction.

Protecting Your Electrical System

Circuit breakers protect your home from catastrophic electrical failure, but not from wear and tear. This type of damage builds up over years and isn’t covered by home insurance. Restoring internal wiring can be expensive, but Agway helps by providing $1,000 worth of coverage when repairs are needed.

Our EnergyGuardTM Program covers your heating, cooling, and electrical systems.* Instead of paying a technician out of pocket when the need for repair occurs, our customers contact us. We send a contractor to your door and pay for all covered parts. There are no service fees or deductibles either. Contact us today to start saving on repairs!

*Coverage depends on which commodity you purchase.