Introduction

Thomas Edison patented a fuse for his electrical distribution system in 1890. Over 100 years later, fuses are still used to protect electrical wiring and equipment from damage due to surges and overload conditions.

If you think that the fuse predated the circuit breaker by decades, you would be right, sort of. Thomas Edison patented a circuit breaker design in 1879, eleven years before his fuse patent, even though the use of fuses predates that. (Thomas Edison must have gotten the idea to patent the fuse after watching all of those early light bulb filaments melt before his eyes.) Louis François Clément Breguet pioneered the use of fuse devices to protect telegraph wires from lightning strikes as far back as the 1860’s.

With both of these types of circuit protection being around since the post-U.S. Civil War reconstruction era, which one is better? If you read the literature from a company that primarily makes electrical fuses for industrial applications, the fuse is a superior solution. And, if you read the literature from a company that makes CBE’s (Circuit Breakers for Equipment), the circuit breaker is the best choice. So, which is it? After reading a lot of literature on both sides of the argument, the answer is both, or neither. If one was the runaway winner for all applications, we would know by now.

A circuit breaker is an electromechanical device. Even the simplest circuit breaker is more complicated than the most complicated fuse.

What are the benefits of a circuit breaker, over a fuse?

• Circuit breakers are dead front. Fuses have exposed live parts.
• Circuit breakers can be tested for proper operation. To truly test a fuse, it would need to be destroyed in the process. It is a sacrificial device.
• A fuse can arc, if replaced under power. (Despite the instructions from the manufacturer NOT to replace a fuse under power.) There are some new busbar miniature circuit breaker systems that are designed to have the breakers replaced under power, but adoption has not been wide spread.
• A fuse does not offer magnetic protection, only thermal. This dual trip-curve feature of a circuit breaker makes them unique compared to fuses.
• Circuit breakers have external status indication. Some fuses offer an external fuse blown indication.
• A circuit breaker can be used and an ON/OFF switch.
• A blown fuse can be easily replaced with the wrong size, or even jerry-rigged (using a wire or small copper bar to replace the fuse) creating a safety issue.
• Start-up tripping is an issue with fuses (need to oversize the fuse for inrush current). Fuses can require larger wiring to compensate for inrush current.
• A circuit breaker can provide ground fault protection, a fuse cannot.
• Fuses “age” and degrade over time which can cause nuisance tripping.
• Single phasing on three-phase loads does not happen with a three-pole circuit breaker. All circuits trip at once. Using individual fuses for a three-phase power can result in single phasing and equipment damage.

That’s a long list of the benefits of a circuit breaker, but what are the benefits of a fuse, over a circuit breaker?

• Fuses are simple and straight forward to use.
• Fuses trip faster than a circuit breaker.
• Fuses are initially less expensive than circuit breakers.
• Fuses have a smaller footprint in a control cabinet.
• There are a variety of fuse types for different applications.
• Fuses can be more reliable over time, because they do not have moving parts.
• Fuses do not require regular maintenance. Molded Case Circuit Breakers and others, do.
• Because a fuse is replaced every time after an overcurrent trip, the same level of circuit protection performance is guaranteed. A circuit breaker can wear out if it trips too many times.

Where does this leave us? Fuses offer circuit protection that is inexpensive, straightforward and fast protection. Their faster circuit protection time is perhaps their biggest benefit over circuit breakers. This is important when protecting sensitive electronic equipment. Circuit breakers provide better protection for three-phase applications. Because circuit breakers are NOT sacrificial, do not require replacement, as a fuse does, power can be more quickly restored without the need to hunt down a spare fuse. Consider the application, where it will be located, (remote or local), and the operating environment. Both fuses and circuit breakers will continue to have their place in electrical equipment installations.

Is the Overcurrent Protective Device Rated for the System Voltage?

When selecting an overcurrent protective device, it's crucial to ensure it matches the system voltage. An overcurrent protective device rated for the system voltage guarantees it can handle the electrical load without malfunctioning or posing safety risks.

If a device is not rated for the correct voltage, it might fail and cause equipment damage or safety hazards. Always check the voltage rating on the device's label or specification sheet to ensure it matches your system's needs. This compatibility is essential for protecting both the equipment and the entire electrical system.

What is the Maximum Fault Current that the Protective Device is Designed to Interrupt?

When it comes to electrical systems, safety is paramount. One critical factor to consider is the maximum available fault current that a protective device might need to interrupt.

Fault current refers to the excessive electrical current that occurs during a fault condition, such as a short circuit. This surge can be dangerous, causing damage to electrical parts, fire hazards, and even injuries.

Factors Influencing Fault Current

Several variables affect the maximum available fault current:

• System Voltage: Higher voltages can result in higher fault currents.
• Impedance: Lower impedance in the electrical path means higher fault current levels.
• Equipment Ratings: The capacity and design of transformers, generators, and other equipment play a crucial role.

Why It Matters

A protective device, like a circuit breaker or fuse, must be able to handle the maximum available fault current to ensure it disconnects power swiftly and safely. If it fails to do so, the consequences can be serious, including equipment damage and major safety risks.

Disclaimer:
The content provided is intended solely for general information purposes and is provided with the understanding that the authors and publishers are not herein engaged in rendering engineering or other professional advice or services. The practice of engineering is driven by site-specific circumstances unique to each project. Consequently, any use of this information should be done only in consultation with a qualified and licensed professional who can take into account all relevant factors and desired outcomes.

The information was posted with reasonable care and attention. However, it is possible that some information is incomplete, incorrect, or inapplicable to particular circumstances or conditions. We do not accept liability for direct or indirect losses resulting from using, relying or acting upon information in this blog post.