Key Takeaways
- Type 1 SPDs are the first line of defense at the service entrance; Type 2 SPDs are the second line, protecting downstream panels and equipment.
- The choice between Type 1 and Type 2 depends more on installation location and exposure than on kA rating alone.
- For many systems, a layered approach with Type 1 plus Type 2 provides better overall protection than a single device.
- Uc, Up, Iimp, In, Imax, and SCCR all matter, but installation quality and grounding are equally important.
- NEC 2023 now requires SPD protection for many dwelling‑unit services, so the question is often not “do I need an SPD?” but “what type and where should it go?”
Surge protective devices (SPDs) are essential for protecting electrical systems from transient overvoltage. If you are choosing between Type 1 and Type 2 SPD, the most important question is where the device will be installed and how much energy it must handle.
What Is an SPD?
An SPD is a device that limits transient voltage and diverts surge current away from sensitive equipment. It does not block every surge, but it reduces the voltage seen by downstream loads to a level that the equipment is designed to withstand.
Type 1 vs Type 2 SPD
Type 1 and Type 2 SPDs are designed for different roles and different surge environments.
- Type 1 SPD is typically installed at the service entrance or main service equipment, on or near the line side of the service disconnect. It is intended to handle high‑energy external surges, including those associated with lightning or utility switching.
- Type 2 SPD is typically installed on the load side of the main disconnect, at the main panel, sub‑panel, or distribution board. It is intended to protect against residual surge energy and internal switching transients after the first level of protection.
In many systems, Type 1 and Type 2 work together: Type 1 takes the initial surge blow, and Type 2 reduces what remains before it reaches sensitive equipment.
Type 1 SPD Overview
Type 1 SPDs are usually the first barrier between the power supply and the internal electrical system. They are often used in buildings that require whole‑facility protection or that face higher lightning exposure, such as overhead service, exposed infrastructure, or industrial sites.
Key points:
- Commonly used at or near the service entrance.
- Designed to handle high‑energy surges, often using 10/350 μs test waveforms.
- Often rated for higher impulse current (Iimp) and higher withstand capability.
- Typically used when there is a higher risk of external lightning‑related events.
Type 2 SPD Overview
Type 2 SPDs are usually installed downstream at the distribution level, where they protect branch circuits and connected equipment. They are the most common choice for panel‑mounted surge protection in residential, commercial, and many industrial systems.
Key points:
- Installed on the load side of the main disconnect, in the main panel, sub‑panel, or equipment cabinet.
- Designed to handle residual and internally generated surges, typically using 8/20 μs test waveforms.
- Often optimized for lower voltage protection level (Up), which is important for sensitive electronics.
- Commonly used to protect HVAC systems, motor control centers, IT rooms, and automation panels
Type 1 SPD vs Type 2 SPD Comparison Table
| Item | Type 1 SPD | Type 2 SPD |
| Typical location | Service entrance, main distribution point | Distribution panel, sub-panel |
| Main role | First-line protection from high-energy surges | Secondary protection from residual and internal surges |
| Common application | Whole-building protection | Branch circuit and equipment protection |
| Installation side | Line side or service entrance, depending on listing | Load side of main disconnect |
| Best use case | High-exposure entry protection | Downstream protection for panels and loads |
How SPD Surge Protection Works
When a surge occurs, the SPD provides a low-impedance path that diverts excess current away from equipment. At the same time, it clamps the voltage to a safer level so the connected system is less likely to suffer damage.
The real performance of an SPD depends not only on the device itself, but also on how and where it is installed. Longer lead wires increase inductance and can raise the actual let-through voltage seen by equipment.
Why SCCR Matters
Short-circuit current rating (SCCR) is critical for safety and installation compliance. The SPD must be able to withstand the available fault current of the electrical system without creating a hazard.
How to Choose the Right SPD in 5 Steps
Choosing the right surge protective device is not only about deciding between Type 1 and Type 2. A suitable SPD should match the installation point, system voltage, surge exposure, and safety requirements of the electrical system. The following five steps can help you make a more reliable selection.
Step 1: Identify the Installation Point
Determine where the SPD will be installed. If the device will be installed at the service entrance or main distribution point, a Type 1 SPD is often preferred for primary surge protection. If the device will be installed downstream in a distribution panel, sub-panel, or equipment panel, a Type 2 SPD is usually the more suitable choice.
Step 2: Check the System Voltage and Grounding Type
The SPD must match the actual system voltage and grounding arrangement. Before selecting a product, confirm whether the system is single-phase, three-phase, TN, TT, IT, or another configuration.
The UC or MCOV rating should be suitable for the normal operating voltage of the system. If the voltage rating is too low, the SPD may fail prematurely. If it is too high, the protection level may not be effective enough for sensitive equipment.
Step 3: Compare the Surge Current Ratings
Next, check the surge current ratings that apply to the SPD type. For Type 1 SPDs, Iimp is an important rating because it indicates the device’s ability to withstand high-energy impulse currents. For Type 2 SPDs, In and Imax are commonly used to evaluate discharge current performance.
A higher surge current rating may be needed for buildings with overhead power lines, exposed outdoor equipment, industrial loads, or higher lightning risk.
Step 4: Review the Voltage Protection Level
The voltage protection level, or Up, shows how much voltage may pass through to downstream equipment during a surge. In general, a lower Up value means better protection for connected devices.
However, Up should be considered together with the installation method. Even a high-quality SPD may perform poorly if the connecting leads are too long or routed incorrectly.
Step 5: Verify SCCR and Installation Requirements
Finally, confirm that the SPD’s SCCR is suitable for the available fault current at the installation point. This is important for electrical safety and compliance.
You should also check installation requirements such as conductor size, lead length, backup protection, panel space, and applicable electrical codes. Proper installation is essential for the SPD to perform as intended in real surge conditions.
When to Use Type 1 SPD
Type 1 SPD is usually the right choice when you want primary protection at the service entrance. It is especially useful in buildings with overhead service, exposed infrastructure, or high lightning exposure.
Common use cases include commercial service entrances, industrial switchboards, and whole-building protection strategies.
When to Use Type 2 SPD
Type 2 SPD is usually used at distribution panels or sub-panels where it protects circuits from residual surge energy. It is a practical choice for common building systems and sensitive loads.
This includes HVAC equipment, motor control centers, IT rooms, automation panels, and other branch-level loads. T
Type 1+Type 2 Combined Protection
In many installations, the best solution is a coordinated Type 1+Type 2 strategy. Type 1 handles the incoming surge at the entry point, while Type 2 reduces the remaining surge energy farther downstream.
This layered approach improves overall protection and is widely used in commercial, industrial, and high-value facilities.
NEC 2023 SPD Requirements
The NEC 2023 update requires surge protection for services supplying dwelling units under Article 230.67. The SPD must be Type 1 or Type 2 and installed as part of the service equipment or immediately adjacent to it.
This means SPD protection is no longer just an optional upgrade in many residential service applications. It is now a code-driven requirement for dwelling-unit services.
Common SPD Selection Mistakes
One common mistake is choosing an SPD based only on price or basic type designation. Another is ignoring voltage ratings, SCCR, or installation location.
Other mistakes include using long lead wires, failing to coordinate upstream and downstream devices, and assuming one SPD can protect every point in the system. These errors often reduce protection performance more than users expect.
FAQs
Is Type 1 SPD better than Type 2 SPD?
Not always. Type 1 is usually better for service‑entrance protection, while Type 2 is better for downstream panel protection. The choice depends on location and exposure.
Can Type 2 SPD be used at the main panel?
Yes, in some systems, especially where external lightning exposure is low. However, in higher‑risk systems, Type 1 or a Type 1 + Type 2 combination is often preferred.
Do I need both Type 1 and Type 2 SPDs?
For many commercial and industrial systems, yes. A layered strategy usually provides better overall coverage than a single device.
What is the most important factor in SPD selection?
Start with the installation location. A Type 1 at the wrong panel may do less than a well‑placed Type 2. Once the location is confirmed, check voltage rating, Up or VPR, surge current ratings, and SCCR in that order.
Conclusion
Most surge damage is not from a single, direct lightning strike, but from residual energy that travels through the system after the first hit. That is exactly why one device at the entrance is often not enough. A Type 1 SPD at the service entrance handles the initial surge, while a Type 2 SPD downstream catches what gets through.
Need help choosing the right Type 1 or Type 2 SPD for your project? Share your system voltage, installation point, and application environment, and our team can recommend a suitable surge protection solution.
