Circuit Breakers in Your PCB and Your Bill of Materials

Zachariah Peterson
|  Created: December 7, 2018  |  Updated: March 5, 2023
Circuit Breakers in Your PCB and Your Bill of Materials

Circuit breakers are not required in every system, but in some environments they are the main source of protection against overvoltage/high current, as well as any damage that can result from power surges. Circuit breakers are best known for use in residential circuit protection, but they can be used in any environment (such as power systems and industrial systems) that require circuit protection. Some circuit breakers can be mounted on a PCB, while others are too large and must be panel-mounted in an enclosure.

Which one of these options should you choose for your design? We'll outline how to choose between these circuit breakers and outline how to specify these in your assembly.

Circuit Breakers in Your PCB

If your PCB contains sensitive elements that you need to protect from a system fault at high current, you will likely need to include a circuit breaker in your PCB. Circuit protection may also be required under applicable EMC regulations or industry standards for your product, and such circuit protection requirements might warrant a circuit breaker. There are many types of circuit breakers that can be included in your PCB, protecting your circuit from either AC or DC overvoltage and/or inrush currents.

There are four types of circuit breakers:

  • Thermal - tripped by excessive heating during overcurrent conditions
  • Magnetic - trips by the magnetic field generated by a current
  • Thermal-magnetic - involves bending of a bimetal armature at high current
  • Hydraulic-magnetic - magnetic force acts on a spring in a dampening fluid to trip the breaker

Each type of circuit breaker has a different current trip profile over time and distinct mechanical characteristics. Purely magnetic circuit breakers without hydraulic delay use a solenoid to break a current surge and are by far the fastest circuit breakers among the four options.

PCB-Mount vs. Panel-Mount

Circuit breakers are available that can mount directly to a PCB, while larger circuit breakers normally mount to a panel on a housing or cabinet. Low-cost circuit breakers that can be mounted on a PCB are availalbe with current trip ratings of tens of Amps. 

PCB mount circuit breaker
PCB-mount circuit breaker

Protecting a PCB from overcurrent requires some idea of the level of current that will propagate in the circuit once a fault occurs. There are a number of fuses and circuit breakers you can use that will mount to a larger PCB that can withstand on the order of 10 A of current. For example, the 1410-L110 series circuit breaker is a single-pole, press-to-reset, thermal circuit breaker with extremely fast switching. This circuit breaker easily attaches to your PCB as a through-hole component.

Other circuit breakers come in the double-pole variety and are typically used with circuits that require larger appliances. Something more heavy duty, like a Merlin Gerin circuit breaker, cannot be mounted on a PCB and must be mounted to the external packaging of your device. However, they can provide significant protection in the case of short circuit and prevent your board from failing or catching on fire, especially in a high power system.

Selecting the Right Circuit Breaker

Some engineers will oversize their circuit protection to avoid accidental tripping, but they often specify a circuit breaker rated much higher than they should. The current rating on a circuit breaker tells you the maximum current that the circuit breaker can maintain at room temperature. For example, a 10 A circuit breaker will maintain a 10 A current without tripping. A typical 4A circuit breaker with a slow trip profile can tolerate a momentary 10 A current surge without nuisance tripping.

There are various terms used to describe the performance of circuit breakers. Terms like “ignition protection”, “water-proof”, and “dust-proof” are used to describe circuit breakers. However, these terms leave room for ambiguity unless specific industry standards are specified in the component documentation. You should always compare the specified standards for your circuit breaker with your intended application when selecting protection for your board. Make sure to include the relevant standards in your bill of materials.

Circuit breakers with plug-in style terminals are easy to install and replace. They can also be soldered, especially circuit breakers with through-hole terminals. Obviously, screw terminal connections are more secure and suited for applications with high current and in environments where vibration may become a problem. Not all screw terminal circuit breakers can be attached to your PCB through mounting holes, and you will need to examine these breakers before attempting to include them in your PCB.

Modular circuit breakers in an electrical cabinet

Heavy duty circuit protection in an industrial system

What to Include in Your Bill of Materials

If you’re send an entire assembly (including wiring, cable harnesses, enclosure, etc.) into a contract manufacturer for volume production, then any components that are part of the assembled product should be included in the bill of materials. This includes any circuit breaker that will connect to the PCB. This should also include any screw terminal block and flying leads that will provide the required electrical connections back to the PCB.

If you are only sending a PCB in for assembly, and the circuit breaker will be mounted on the PCB, then it should be included in the bill of materials for the assembler. If there will be on-the-line in-circuit testing with the assembled board (checking that the breaker trips), the assembler needs to know the voltage and current that trips the breaker; this can be included in the component description for the bill of materials.

Whenever you need to include components like a circuit breaker in your assembled product, make sure you use the complete set of PCB design tools in Altium Designer® to design your PCB. Altium Designer includes wire harness design capabilities that can check logical connections back to external components like a circuit breaker, as well as custom wiring harnesses and cable assemblies. When you’ve finished your design, and you want to release files to your manufacturer, the Altium 365 platform makes it easy to collaborate and share your projects.

We have only scratched the surface of what’s possible with Altium Designer on Altium 365. Start your free trial of Altium Designer + Altium 365 today.

About Author

About Author

Zachariah Peterson has an extensive technical background in academia and industry. He currently provides research, design, and marketing services to companies in the electronics industry. Prior to working in the PCB industry, he taught at Portland State University and conducted research on random laser theory, materials, and stability. His background in scientific research spans topics in nanoparticle lasers, electronic and optoelectronic semiconductor devices, environmental sensors, and stochastics. His work has been published in over a dozen peer-reviewed journals and conference proceedings, and he has written 2500+ technical articles on PCB design for a number of companies. He is a member of IEEE Photonics Society, IEEE Electronics Packaging Society, American Physical Society, and the Printed Circuit Engineering Association (PCEA). He previously served as a voting member on the INCITS Quantum Computing Technical Advisory Committee working on technical standards for quantum electronics, and he currently serves on the IEEE P3186 Working Group focused on Port Interface Representing Photonic Signals Using SPICE-class Circuit Simulators.

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