Conventional circuit breakersand fuses are unable to fully meet the requirements of SPD protection devices for the following reasons:
When SPD degrades and malfunctions, it may enter a short-circuit failure state.

Miniature circuit breakershave insufficient breaking capacity, and molded-case circuit breakers and fuses may not respond promptly.
Without robust protective devices, it may lead to fires or explosions, resulting in tripping and widespread power outages.
When SPD lacks surge resilience, conventional circuit breakers and fuses cannot entirely meet the requirements of SPD protection devices. The Special Circuit Breaker (SCB) can intervene before an SPD ignites, promptly disconnecting the branch circuit, eliminating the fire hazard at its inception, and protecting the SPD and the distribution system.
Why can SCB replace conventional circuit breakers and fuses to meet SPD protection requirements?

Dc Circuit Breaker
First, let’s get acquainted with SCB:
SCB, which stands for Special Circuit Breaker, is a device used for overcurrent protection at the front end of Surge Protectors (SPD).

The core of an SPD is an oxide varistor, consisting of grains separated by grain boundary layers with a P-N junction semiconductor structure. These grain boundary layers determine the V-I characteristics of the varistor. When a surge current through the varistor exceeds its capacity, some grain boundary layers within the ceramic body become damaged, causing a drop in varistor voltage, and in severe cases, breakdown occurs. With an increase in the number of discharges, performance gradually deteriorates. When it fails, it often takes the form of a short circuit. When an exceptionally large surge passes through the SPD, the oxide varistor component gets damaged before the heat is transferred to the thermal fuse mechanism. If it ruptures, the discharge path is naturally cut off. However, if it fails as a short circuit, because the heat hasn’t reached the point of melting the thermal fuse, it is essential to rely on the SCB to cut off the power.

Regardless of whether it’s an SCB, a backup protector, or circuit breakers andfuses, all of them provide overvoltage protection. But does this mean they will trip when struck by a lightning current, and will the SPD still function, effectively providing lightning protection?

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Firstly, it’s crucial to note that SPDs are connected in parallel within the power line, and the response time of SCBs, circuit breakers, and fuses is not on the same level as SPDs. SPDs operate in nanoseconds, significantly faster than overcurrent protection devices. Installing overcurrent protection devices in front of SPDs is a backup protection measure to prevent accidents in case SPDs fail or short-circuit, leading to fires and equipment damage.

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In practice, however, circuit breakers and fuses may not coordinate well with SPDs, primarily for the following reasons:

They may mistakenly trip during lightning strikes, rendering lightning protection ineffective.
When SPDs short-circuit, they may not interrupt the power flow. Circuit breakers and fuses have rated breaking currents, and in the event of SPD failure or a short circuit, if they cannot provide several times the rated transient current of circuit breakers and fuses (e.g., a C32 circuit breaker would require providing a transient current of 320A), SPDs may potentially cause fire accidents.
SCB surge protection devices are designed to overcome the shortcomings of circuit breakers and fuses. They can work in perfect harmony with SPDs:

High surge current tolerance, ultra-low residual voltage, and immunity to significant lightning surge currents ensure effective lightning protection for SPDs.
Current breaking values range from 3A to 100A, ensuring that SPDs do not catch fire, explode, or trip prematurely, thus safeguarding the electrical grid and electrical safety.
Therefore, SCB backup protectors are far superior to circuit breakers and fuses as overcurrent protection devices. They can replace these devices, installed in series at the front end of SPDs, providing full backup protection and achieving the best lightning protection results.