What Is a Thermal Circuit Breaker? Types & Uses

Electrical systems can overheat and overload—and when that happens, components can become damaged or pose a safety hazard.

That's where thermal circuit breakers come in. They automatically cut off power when the temperature or current exceeds a safe level to prevent damage or failure.

Understanding how circuit breakers work and the different types available will help you choose the right solution for your equipment.

A thermal circuit breaker is a protection device that shuts off power to prevent electrical devices from overheating or overcurrent. It uses a bimetallic strip that bends when the current gets too high.

When the strip reaches a specific temperature, it trips and opens the circuit. Once it cools down, it can be restarted by an automatic or manual reset.

Thermal breakers are often used in home appliances, industrial machinery, automotive systems, and other electrical equipment.

A thermal circuit breaker uses heat to detect when electrical currents are too high. Inside the breaker is a bimetallic strip composed of two metals with different thermal expansion rates. When too much current flows through, it generates heat, and one metal expands more than the other.

This uneven expansion causes the strip to bend and contacts to open, breaking the circuit. This prevents damage from excessive current or overheating.

After tripping, the breaker stays open until the temperature drops. It will either reset automatically once it has cooled down or require a manual reset to restore the connection.

The simplicity and reusability of thermal circuit breakers make them a reliable solution for many types of electrical protection.

There are two main types of thermal circuit breakers:

• Automatic Reset

An automatic reset thermal breaker reconnects the circuit once it has dropped down to a safe temperature. Power is restored automatically when the bimetallic strip returns to its standard shape.

It's often used in systems where temporary overloads can happen but aren't a safety risk, such as in small motors, lighting circuits, or battery-powered devices.

• Manual Reset

A manual reset breaker stays open after it is activated until someone presses a reset button. This design ensures that the system doesn't restart automatically without inspection or manual intervention.

It's essential in applications where safety checks are required before restarting. Manual reset breakers are commonly found in power tools, industrial equipment, or electrical panels.

Thermal circuit breakers are a practical solution for protecting electrical devices from excess heat and current. They're widely used in everyday appliances, commercial equipment, vehicles, and industrial machinery:

• Home Appliances

In your home, thermal circuit breakers are typically used as fuse replacements or built-in protection for everyday devices.

They protect blenders, chargers, lighting, electronic components, outlets, power strips, and extension cords by cutting off power during overloads.

• Industrial Equipment

Thermal circuit breakers help maintain a safe and stable operation in industrial environments. They protect equipment from damage caused by overheating or electrical overloads during heavy use or continuous operation.

You can find them in woodworking machines, printed circuit boards, generators, air compressors, welding machines, power supplies, lawnmowers, planers, and floor-standing circular saws.

• Commercial Equipment

Many commercial and office systems also rely on thermal protection to ensure safety and avoid equipment downtime.

Common uses include copiers, broadcast equipment, PDUs (power distribution units), UPS systems, medical devices, amplifiers, conference systems, and floor scrubbers.

• Automotive Applications

From electric vehicles to boats and portable generators, thermal circuit breakers are used to protect a variety of mobile systems.

They're ideal in systems where space-saving, reliable protection is essential, such as in car starters, electric trailers, mobility aids, marine gear, and fitness machines.

• Motors and Pumps

Systems like AC/DC motors, hydraulic pumps, and water pumps operate under high or variable loads. Thermal breakers are used in these cases to interrupt power before overheating can cause damage.

When picking a thermal circuit breaker, it's important to consider both the technical specs and how it will be used:

• Current Rating

The current rating indicates the maximum amount of current the breaker can handle during normal operation. It should match your application's expected load to avoid false trips or insufficient protection.

• Voltage Rating

The voltage rating determines the highest voltage the breaker can safely interrupt the current flow.

It should always be equal to or greater than your system's operating voltage so the breaker can safely disconnect the circuit without arcing or damage during an overload.

• Trip Time

Trip time is the amount of time it takes the breaker to respond to overcurrent. Some applications, such as medical devices, may require rapid trips for sensitive components, while others, like heating systems, aren't affected by a slower response time.

• Reset Type

Decide between automatic and manual reset depending on whether you want the system to restart automatically or with human assistance.

Manual reset adds a layer of safety control, while automatic reset offers convenience for non-critical systems.

• Mounting Requirements

How and where will the breaker be installed? Thermal circuit breakers are available in various mounting options, including panel-mounted, surface-mounted, or integrated into a device.

Choose a mounting type that matches your installation space to make access easier, especially if manual resets are needed.

• Compliance or Certifications

Depending on the market or industry you are in, you may need circuit breakers that meet regional or international safety standards:

UL (United States)

CSA (Canada)

VDE (Germany)

CCC (China)

Sang Mao's thermal circuit breakers deliver performance you can count on. Trusted by businesses worldwide, our solutions comply with the safety and certification standards of international and regional markets.

Decades of experience has allowed us to develop compact, durable designs that hold up under pressure. Browse our full collection of thermal circuit breakers here.

Whether you're designing consumer electronics, industrial machines, or mobile systems, Sang Mao has the right fit — Get in touch now!