What Is a Surge Protected Breaker?
“Surge protected breaker” is not a formal standard term, but a common industry name for a circuit breaker with integrated surge protection or a combined breaker + SPD unit. It usually refers to two types of products:
- An SPD Specific Disconnector (SSD) for SPDs, used to disconnect the circuit when the SPD fails or shorts. It is also known as a dedicated backup circuit breaker (SCB).
- A combined device that integrates a miniature circuit breaker (MCB/MCCB) with an SPD module, marketed as a “surge protection circuit breaker.”
How Does a Surge Protected Breaker Work?
The core principle of a surge protected breaker remains “breaker for overcurrent, SPD for overvoltage.”
Under normal voltage, the SPD section presents high impedance and conducts almost no current. When a transient overvoltage occurs (e.g., lightning strike or switching operation), nonlinear components inside the SPD (such as MOVs or GDTs) switch to low impedance within nanoseconds, diverting surge current to the grounding system and limiting the voltage at the load to a safe level.
The breaker section provides standard overload and short‑circuit protection; if the SPD fails short‑circuit, the associated SCB or upstream MCB trips to disconnect the faulty SPD from the system and prevent fire.
Is a Surge Protected Breaker the Same as an SPD?
Surge Protected Breaker vs. Surge Protective Device
A surge protected breaker is not the same thing as a surge protective device. An SPD is the component that clamps and diverts transient overvoltage to earth. The term surge protected breaker usually describes a breaker used as the backup overcurrent device for an SPD, or a combined product that houses both functions. The SPD does the surge clamping; the breaker provides overcurrent and short-circuit protection and a means to disconnect the SPD branch for maintenance.
Can an SPD Replace a Circuit Breaker?
No, an SPD cannot replace a circuit breaker. The two devices protect against entirely different electrical conditions. An SPD limits transient overvoltage and has no way to detect or interrupt a sustained overload. Without a breaker, a fault overload would continue to feed energy into the system until the wiring overheats or the SPD fails. Both devices are required, and neither can substitute for the other.
Why Circuit Breakers and SPDs Work Together
Circuit breakers and SPDs work together because each covers a gap left by the other. The breaker protects the wiring and the SPD branch against overcurrent and short circuits. The SPD protects the sensitive electronics against voltage transients that the breaker cannot even see. In a correctly coordinated system, the SPD is installed behind a dedicated backup breaker, so that if the surge components degrade into a short circuit, only the SPD branch is disconnected and the rest of the installation keeps running.
Protection Function | Circuit Breaker | Surge Protective Device (SPD) |
|---|---|---|
Primary threat handled | Overcurrent and short circuit | Transient overvoltage (surges) |
Response quantity | Excess current | Excess voltage |
Response speed | Milliseconds to seconds | Nanoseconds |
Connection | In series with the circuit | In parallel across the supply |
Purpose | Prevent wiring fires | Protect sensitive electronics |
Can it replace the other? | No | No |
What Size Circuit Breaker Is Needed for an SPD?
Why an SPD May Require Backup Overcurrent Protection
An SPD is connected in parallel across the supply, so a failure of its internal components can become a line-to-earth short circuit. Backup overcurrent protection is required to disconnect the SPD branch safely in this situation. Without it, an SPD fault could trip the main breaker or present a fire hazard. The backup breaker also provides a convenient means to isolate the SPD for testing or replacement.
How to Select the Correct Backup Circuit Breaker
The correct backup breaker rating depends on the SPD model and the prospective short-circuit current at the installation. General guidance often recommends around 32 A for a 40 kA Type 2 SPD and around 63 A for a 100 kA Type 2 SPD, but the only reliable method is to follow the ratings declared in the SPD manufacturer’s datasheet and coordination tables.
Follow the SPD Manufacturer’s Installation Requirements
IEC 61643-11 requires SPDs to be installed according to the manufacturer’s technical documentation. Manufacturers test the coordination between the SPD and its backup device, so deviating from their specified fuse or breaker ratings can compromise the voltage protection level, cause nuisance tripping, or invalidate certification and warranty. Always use the manufacturer’s recommended backup protection.
Typical SPD Rating | Common Backup Breaker Guidance | Purpose |
|---|---|---|
20 kA Type 2 | 20 A to 32 A | Sub-distribution surge protection |
40 kA Type 2 | 32 A to 40 A | Commercial and light industrial boards |
100 kA Type 2 | 63 A | High-surge commercial/industrial |
Type 1 (Iimp 12.5 kA) | 80 A to 125 A+ | Main service entrance |
Type 1 (Iimp 25 kA) | 160 A gG fuse equivalent | Severe lightning exposure |
How Is a Surge Protected Breaker Connected to an SPD?
A surge protected breaker and an SPD are normally coordinated as part of the same surge protection branch. When an external backup circuit breaker or Surge Protective Device Circuit Breaker (SCB) is required, the breaker is connected in series with the SPD branch. This allows the breaker to disconnect the SPD if the SPD fails and develops a sustained short circuit, while also providing a convenient way to isolate the SPD for maintenance or replacement.
However, this does not mean that the SPD itself is connected in series with the electrical load. The SPD is normally connected in parallel with the protected circuit. Under normal operating conditions, the SPD remains in a high-impedance state and does not interrupt the normal power supply. When a transient overvoltage occurs, the SPD rapidly conducts and diverts the surge current through the appropriate protection path, such as the protective earth (PE), limiting the voltage reaching downstream equipment.
The basic connection principle can therefore be expressed as:
Power Supply → Backup Breaker/SCB → SPD Branch
while the SPD protection path is:
Line/Neutral → SPD → PE/Ground
The backup breaker and SPD must be properly coordinated according to the SPD manufacturer’s specifications. The breaker rating should not be selected solely based on the SPD’s surge current rating, such as Imax or In. The correct backup protection depends on the specific SPD design, prospective short-circuit current, conductor requirements, and the manufacturer’s tested coordination.
In short, the backup breaker is connected in series with the SPD branch, while the SPD itself is connected in parallel with the protected electrical circuit. Understanding this distinction is essential for installing a surge protection system correctly and safely.
Conclusion
“Surge protected breaker” is not a single standard device name, but a practical term for solutions that combine overcurrent protection (circuit breaker) with transient overvoltage protection (SPD)—either as an integrated “surge protection circuit breaker” or as an SPD with its dedicated backup circuit breaker (SCB). Its core logic is simple: the breaker handles overload and short‑circuit currents, while the SPD clamps and diverts lightning or switching surges before they reach sensitive equipment.
LSP is a professional manufacturer of Surge Protective Devices, offering AC and DC SPDs and surge protected breakers for residential, commercial, industrial, and renewable energy applications.
Whether you need SPD, or surge protected breaker, LSP can provide solutions tailored to different electrical systems and installation requirements. Contact LSP to discuss your application and find the right surge protection solution for your project.
Frequently Asked Questions About Surge Protected Breakers
Can a circuit breaker protect against power surges?
No, a standard circuit breaker cannot protect against power surges effectively. A breaker reacts to excess current and opens its contacts within milliseconds, but surges are microsecond voltage transients that it does not detect during its normal operation cycle. To stop surges, a dedicated surge protective device must be installed to clamp the transient overvoltage and divert the surge current safely to earth while protecting all of the sensitive downstream equipment connected outside the building.
Does an SPD need a circuit breaker?
Yes, in most installations a surge protective device needs a backup circuit breaker or fuse connected in series with it. This backup device disconnects the SPD branch if the surge components fail into a short circuit, protecting the whole panel and preventing a main breaker trip. It must be sized correctly according to the manufacturer coordination requirements so that it reliably clears a genuine fault without causing any nuisance tripping of the circuit during operation.
What size breaker should be used with an SPD?
The breaker size depends on the SPD rating and the installation details involved. As a general reference, a 40 kA Type 2 SPD often uses around a 32 A breaker, a 100 kA Type 2 SPD uses around a 63 A breaker, and a Type 1 SPD needs a larger rating. The reliable approach is to follow the rating and backup coordination table declared in the SPD manufacturer data sheet for your specific installation site.
Can I install an SPD without a circuit breaker?
In most installations an SPD should not be installed without a backup circuit breaker or fuse. The backup overcurrent device disconnects the SPD branch if the surge components fail as a short circuit, preventing a main-breaker trip and protecting the panel from any damage. Follow the manufacturer coordination requirements to select the correct backup protection rating for your installation project and ensure the surge protective device remains safely coordinated with the overall distribution system design.
