How Do Circuit Breakers Work? Common Reasons for Tripped Circuits

Circuit breakers are essential electrical safety devices found in nearly every home and building. They are designed to protect electrical circuits from damage caused by overcurrents and short circuits. When a circuit breaker “trips,” it disconnects the electricity flowing through the circuit to prevent fires, shocks, and other hazards. Understanding how circuit breakers work and why they trip can help homeowners identify and resolve underlying electrical issues.

What Is a Circuit Breaker and How Does It Work?

A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from overcurrents and short circuits. It monitors the amount of current flowing through a circuit and trips if the current exceeds a safe threshold.

Circuit breakers contain a bimetallic strip or an electromagnet that heats up as current passes through. If the current gets too high, the strip will bend and “trip” the breaker, shutting off the power. Most breakers are designed to trip quickly in response to large overloads but allow a brief period of smaller overloads. This helps prevent nuisance tripping while still protecting from dangerous high currents.

Once a circuit breaker trips, it disconnects the circuit from the power source and must be manually reset to restore power. Resetting involves flipping the breaker all the way to the “Off” position and then back to the “On” position. This mechanism helps ensure that any underlying issue is addressed before power returns.

Where Are Circuit Breakers Located?

In a home, the main circuit breaker panel or service panel is typically located outside near the electric meter or inside in a garage, basement, or utility closet. This panel contains the main shutoff that controls power to the entire house as well as individual breakers for each circuit.

Additional circuit breaker subpanels may be located throughout the home, often in laundry rooms, kitchens, and bathrooms. These subpanels allow circuits to be accessed and controlled at convenient locations rather than requiring access to the main panel for every circuit.

Common Reasons Why Circuit Breakers Trip

There are several reasons why a circuit breaker may trip, interrupting power to parts of your home. Understanding common causes can help troubleshoot tripped breakers.

Overloaded Circuits

One of the most common reasons for a tripped circuit is simply overloading the circuit with more electricity than it was designed for. Plugging in too many appliances on one circuit or operating high-wattage appliances can overload the wiring and cause the breaker to trip.

A circuit is most likely to become overloaded if too many heat-generating devices like hair dryers, space heaters, or air conditioners are used on one circuit. Overloaded circuits are especially common in older homes with outdated wiring. Adding new lighting or appliances without upgrading wiring can also overload circuits.

Short Circuits

A short circuit occurs when electricity flows along an unintended path with little or no resistance. This often happens when hot and neutral wires touch or a hot wire contacts metal conduit or framing. The excessive current flow triggers the circuit breaker instantly.

Short circuits are very dangerous because they can generate tremendous heat very quickly. Common causes include frayed or damaged wires, loose connections, faulty devices and old, cracked insulation. Rodent damage or nails/screws driven through concealed wires can also create shorts.

Ground Faults

A ground fault occurs when some of the current leaks outside the normal path of a circuit and flows into the ground or through water or a person, instead of returning along the neutral wire. This imbalance of current flow trips the breaker.

Ground faults often indicate worn insulation or exposed wires that allow current to escape to earth ground. Wet wiring, water intrusion into appliances, and damaged power cords are common culprits. GFCI outlets are designed to detect and prevent ground faults very quickly to prevent potential electric shocks.

Electrical Surges

Power surges are brief spikes in voltage caused by events like lightning strikes, damage to power lines, faulty appliances and even startup of large motors. While surges are typically only millisecond events, they can cause breakers to trip and damage electronics.

Surges can overload circuits when they cause large instantaneous spikes in current flow. Both external surges coming through the electrical system or internally from appliances can potentially trip breakers. Use of surge suppressors can help protect equipment from damaging surges.

Old/Faulty Breaker

Sometimes a circuit breaker itself is just worn out or defective and trips when it shouldn’t. Breakers contain mechanical components that can weaken over time and not respond as intended. Old breakers made with inferior materials or worn contacts can become prone to nuisance tripping.

Environmental factors like dirt, dust, moisture and corrosion can affect performance. Signs of a faulty breaker include tripping without an overload, not tripping when overloaded, or failure to reset properly. Faulty breakers should be replaced by an electrician.

What To Do When a Circuit Breaker Trips

When a circuit breaker trips and cuts power, follow these steps:

  • Locate the tripped breaker – it will be in a halfway ON/OFF position or clearly labeled as tripped.
  • Unplug devices and turn off switches on the circuit. This removes any loads on the circuit.
  • Flip breaker fully OFF and then back ON to reset it. Check that power is restored.
  • Plug in and turn on devices one at a time. The breaker may trip again indicating an overloaded circuit or faulty device.
  • For repeated trips, move devices to other circuits to isolate the issue. Call an electrician if needed.
  • For tripped GFCI outlets, press RESET button. If it won’t reset, that outlet may be faulty and need replacement.
  • Install surge suppressors to protect electronics if surges are suspected. Consider whole house surge protection.
  • Replace any damaged cords or devices that may be causing shorts. Check for wiring/insulation damage.
  • Upgrade overloaded circuits – call an electrician to evaluate wiring and install additional circuits.
  • Replace faulty breakers that don’t properly reset or trip.

Properly dealing with tripped breakers is important to ensure safety and prevent nuisance power interruptions and damage. Take time to identify the underlying cause before simply resetting breakers repeatedly.

Frequently Asked Questions

Why does my circuit breaker keep tripping with nothing plugged in?

Frequent tripping of a circuit breaker with no loads on it likely indicates a short circuit somewhere in the wiring. This could be due to damaged insulation, nails/screws through the wires, chewed wires from rodents, or defective devices, cords and connections in the circuit. An electrician should inspect and test the circuit to identify the fault.

Why does the circuit breaker trip when I plug in or turn on appliances?

This is most commonly caused by an overloaded circuit, especially with high-wattage appliances like hair dryers, microwaves and space heaters. Check the wattage ratings of devices and use different circuits to share the load. Upgrading wiring may be needed if circuits are outdated and amperage too low.

Is it safe to use a 15-amp circuit for 20-amp appliances?

No, this defeats the overload protection designed into the system. Appliances labeled as requiring 20 amp circuits have a peak power draw that can trip a 15-amp breaker under normal use. Always use properly rated circuits to avoid overloading.

Why does my circuit breaker not trip even when overloaded?

If a circuit breaker does not trip and shut off power when overloaded, it is defective and fails to provide full protection. This is a potential fire hazard if wires overheat. Test the breaker or have an electrician inspect and replace it if faulty.

What size circuit breaker do I need for a room air conditioner?

Most room A/C units will require a dedicated circuit with appropriate wire size and 15 or 20 amp breakers, depending on wattage. Always check the manufacturer’s specifications for recommended circuit breaker amperage to match the unit. Undersized breakers can trip repeatedly.

Can I increase circuit breaker size to avoid tripping?

No, only use a breaker rated for the actual wire size used in the circuit. Larger breakers will not properly protect undersized wiring from overheating. Breakers must match wire gauge – upgrading wiring is necessary to increase breaker size safely.

Why does my circuit breaker make a buzzing or humming noise before tripping?

Electrical arcing and excessive heat buildup in the breaker can cause buzzing, humming or sizzling sounds prior to tripping. This is an indicator the circuit is being dangerously overloaded. Immediately power down any devices and call an electrician to inspect for faulty wiring or equipment.


Circuit breakers are indispensable guardians of electrical safety in modern homes, commercial buildings and industry. When cared for and maintained properly, they silently stand watch, ready to instantly cut power during potentially hazardous electrical faults. Understanding how circuit breakers function and heeding warning signs of underlying problems will help keep your home’s electrical system running safely for years to come.