SPD Selection Guide: Choose the Right Surge Protective Device
A practical surge protective device selection guide for engineers, panel builders, solar EPCs, distributors, and OEM buyers. Compare AC vs DC SPD, Type 1 vs Type 2 vs Type 1+2, voltage rating, poles, discharge current, IEC standards, and installation position.
To choose an SPD, first identify whether the protected circuit is AC or DC. Then select the SPD type by installation position, match Uc or Ucpv to the system voltage, check Iimp, In, Imax and Up, confirm poles and earthing system, and verify backup protection and IEC standard compliance.
Fast Selection Path
AI-ready decision flowAC or DC?
Never use an AC SPD on the DC side of a PV system.
Where is it installed?
Main incoming panel, distribution board, PV combiner box, inverter side, or terminal equipment.
Which SPD type?
Type 1, Type 2, Type 1+2, or Type 3 depends on surge exposure and installation position.
Which voltage and poles?
Check Uc or Ucpv, earthing system, phase count, polarity, and wiring mode.
Which rating and standard?
Confirm Iimp, In, Imax, Up, backup protection, IEC 61643 series, and project requirement.
6 rules for choosing the right SPD
These rules are the fastest way to narrow down the correct surge protective device before checking the final datasheet.
SPD selection by application, circuit and installation position
This table is designed for B2B buyers who need to match a practical SPD direction before choosing a model.
| Application | Circuit | Typical installation position | Recommended SPD direction | Key parameters to check | Related page |
|---|---|---|---|---|---|
| Main incoming panel | AC | Service entrance, main switchboard, first distribution point | Type 1 or Type 1+2 AC SPD | Iimp, Uc, Up, poles, backup protection, earthing system | Type 1+2 SPD |
| Distribution board | AC | Residential, commercial, or industrial sub-panel | Type 2 AC SPD | Uc, In, Imax, Up, 1P/2P/3P/4P, remote signal | SPD for Distribution Board |
| Industrial control panel | AC or DC | Control cabinet, machine panel, automation cabinet | DIN rail SPD, usually Type 2 | Voltage, poles, mounting width, indicator, remote signal, backup protection | DIN Rail Surge Protector |
| PV combiner box | DC | Between PV strings and inverter input | DC Type 2 SPD or DC Type 1+2 SPD | Ucpv, 1000V/1500V DC, In, Imax, Iimp if required, polarity | PV Combiner Box SPD |
| Solar inverter DC input | DC | Inverter DC side, PV input side | 1000V or 1500V DC SPD | Ucpv, PV maximum voltage, Type 2 or Type 1+2, DC disconnection design | Surge Protection for Inverters |
| 1500V solar PV system | DC | Utility-scale PV, high-voltage string inverter system | 1500V DC SPD | Ucpv ≥ maximum PV system voltage, In/Imax, Iimp if Type 1+2 is required | 1500V DC SPD |
| 1000V solar PV system | DC | Residential, commercial, or small ground-mount PV system | 1000V DC SPD | Ucpv, PV string voltage, DC polarity, replaceable module, standard | 1000V DC SPD |
| Sensitive terminal equipment | AC or signal | Near load, controller, communication or sensitive electronics | Type 3 SPD or signal SPD after upstream protection | Uoc, Up, coordination distance, protected equipment withstand voltage | Type 1 vs Type 2 vs Type 3 SPD |
8 steps to select an SPD correctly
Use this process before requesting a quotation or approving a surge protective device for a project.
Identify AC or DC
Check whether the protected circuit is AC distribution, PV DC, battery DC, signal, or equipment-side protection.
Define the location
Main panel, sub-panel, combiner box, inverter input, control cabinet, or terminal equipment require different SPD directions.
Select SPD type
Choose Type 1, Type 2, Type 1+2, or Type 3 according to lightning exposure and protection level.
Match voltage
For AC, check Uc. For PV DC, check Ucpv and maximum open-circuit voltage under cold conditions.
Check discharge rating
Type 1 focuses on Iimp. Type 2 commonly uses In and Imax. Type 3 often involves Uoc and fine protection.
Confirm Up
The voltage protection level should be suitable for the equipment withstand voltage and coordinated with the system.
Confirm poles and wiring
Choose 1P, 2P, 3P, 4P, 3P+N or PV DC configuration according to wiring and earthing system.
Verify standard and backup
Check IEC standard, certification requirement, backup fuse or MCB, short-circuit rating and installation instructions.
AC SPD and DC SPD are not interchangeable
The first selection decision is circuit type. AC and DC SPDs are designed for different voltage behavior, application conditions and test requirements.
Choose AC SPD for AC power systems
AC SPDs are used in low-voltage AC distribution systems, including main panels, distribution boards, industrial cabinets and AC equipment inputs.
Choose DC SPD for PV and DC systems
DC SPDs are used on the DC side of photovoltaic systems, such as PV strings, combiner boxes and inverter DC inputs.
How to choose Type 1, Type 2, Type 1+2 or Type 3 SPD
SPD type should be selected by installation position and surge exposure, not only by the kA number printed on the device.
| SPD Type | Typical position | Main selection meaning | Key parameter | When to consider it |
|---|---|---|---|---|
| Type 1 SPD | Main incoming position or service entrance | Designed for lightning current duty at the entry point of the installation. | Iimp | External lightning protection system, overhead line exposure, high lightning risk. |
| Type 2 SPD | Distribution board, sub-panel, control cabinet | General secondary surge protection against induced surges and switching transients. | In, Imax, Up | Most common choice for distribution boards and many OEM electrical assemblies. |
| Type 1+2 SPD | Main panel or high-exposure system position | Combined device for lightning current capability and secondary surge protection. | Iimp, In, Imax, Up | Main panels, lightning-exposed sites, industrial systems, solar PV projects. |
| Type 3 SPD | Near sensitive terminal equipment | Fine protection close to the protected load, usually after upstream SPD protection. | Uoc, Up | Control electronics, sensitive loads, equipment with lower withstand voltage. |
Choose the correct voltage rating and pole configuration
Many SPD selection errors happen because the voltage rating or pole configuration is chosen too casually.
AC voltage: check Uc
For AC SPDs, the maximum continuous operating voltage is usually shown as Uc. It must be suitable for the actual AC system voltage and earthing arrangement.
Common AC systems include 230/400V and 277/480V, but final selection depends on local network design.PV DC voltage: check Ucpv
For solar PV SPDs, check Ucpv against the maximum DC voltage of the PV string, including cold-temperature open-circuit voltage.
1000V DC and 1500V DC PV systems require PV-rated DC SPDs with matching Ucpv.Poles: match the wiring
Pole selection depends on single-phase, three-phase, neutral arrangement, TT/TN/IT earthing system, and PV DC protection mode.
Common options include 1P, 2P, 3P, 4P, 3P+N and PV DC configurations.| System | Common SPD configuration | What to confirm |
|---|---|---|
| Single-phase AC | 1P+N or 2P SPD | Line, neutral, earthing system, Uc, backup protection. |
| Three-phase AC | 3P, 3P+N or 4P SPD | Neutral arrangement, TT/TN system, panel wiring, phase voltage. |
| PV DC | PV DC SPD module | Positive/negative polarity, Ucpv, 1000V/1500V system, Type 2 or Type 1+2. |
| OEM cabinet | DIN rail pluggable SPD | Module width, remote signal, indicator window, replacement cartridge, wiring space. |
Key SPD parameters buyers should understand
Do not compare SPDs only by one headline kA number. Use the full parameter set to judge whether the device fits the system.
| Parameter | Meaning | Selection use |
|---|---|---|
| Uc | Maximum continuous operating voltage for AC SPD. | Must be suitable for the normal AC system voltage. |
| Ucpv | Maximum continuous operating voltage for PV DC SPD. | Must match or exceed the maximum PV DC system voltage according to design. |
| Iimp | Impulse current rating commonly used for Type 1 SPD. | Important for incoming protection and lightning-exposed systems. |
| In | Nominal discharge current, commonly used for Type 2 SPD. | Indicates repeated surge discharge capability under defined test conditions. |
| Imax | Maximum discharge current for Type 2 SPD under defined test conditions. | Useful for comparison, but should not be the only selection criterion. |
| Up | Voltage protection level. | Lower Up generally means better voltage limitation, but coordination and installation still matter. |
| Uoc | Open-circuit voltage of the combination wave generator, often used for Type 3 SPD testing. | Relevant for fine protection near sensitive equipment. |
| Backup fuse / MCB | Overcurrent protection coordinated with the SPD. | Must follow the SPD datasheet and available fault current. |
| Remote signal contact | Auxiliary contact for remote failure indication. | Useful for PV combiner boxes, industrial cabinets and monitored systems. |
Which IEC standard should you check?
Standards are part of SPD selection. They help confirm whether the device is designed and tested for the correct application.
| Standard | Common application | Why it matters |
|---|---|---|
| IEC 61643-11 | Low-voltage AC surge protective devices. | Used for AC SPD performance, safety requirements, tests and ratings. |
| IEC 61643-31 | SPDs for photovoltaic DC installations up to 1500V DC. | Important for PV combiner boxes, inverter DC inputs and solar DC-side protection. |
| IEC 61643-12 | Application guidance for AC SPD selection and installation. | Useful for coordination, installation position and AC system protection design. |
| IEC 61643-32 | Application guidance for PV SPD selection and installation. | Useful for PV-side SPD placement, selection and coordination. |
| UL 1449 | North American SPD safety standard. | Important when the project requires UL-listed or North America-oriented SPD approval. |
Selection is not complete without installation checks
A suitable SPD can still perform poorly if it is installed in the wrong position or wired incorrectly.
Install near the protected entry point
Main protection should be placed close to the incoming power point or distribution point it protects.
Keep connection leads short
Long and looped wiring increases residual voltage. Keep SPD connection leads short, straight and properly routed.
Ensure proper grounding
SPD performance depends on equipotential bonding and a low-impedance path for surge current.
Coordinate upstream and downstream SPDs
Type 1, Type 2 and Type 3 devices should work as a coordinated protection system, not isolated devices.
Check backup protection
The fuse or circuit breaker must match the manufacturer’s recommendation and the available short-circuit current.
Plan maintenance and replacement
Visual indicators, remote signal contacts and replaceable cartridges make inspection easier in industrial and PV systems.
Common SPD selection mistakes
These mistakes are common in sourcing, panel design and project specification.
Choosing only by Imax
Imax is not the whole selection. Voltage, type, Up, installation position, backup protection and standard are also critical.
Using AC SPD for PV DC
A PV DC circuit needs a DC SPD designed for photovoltaic application and suitable Ucpv.
Ignoring Type 1 requirement
Lightning-exposed buildings and systems with external lightning protection may need Type 1 or Type 1+2 protection.
Wrong voltage rating
Uc or Ucpv must fit the actual system voltage, not only the general system name.
Ignoring earthing system
TT, TN and IT systems may require different protection modes and pole arrangements.
No replacement plan
For PV and industrial systems, visual status, remote signal and replacement cartridge design are important for maintenance.
What information should you send before asking for SPD selection?
Send these details to get a faster and more accurate recommendation from an SPD supplier.
| Information | Example | Why it matters |
|---|---|---|
| System type | AC distribution board, PV DC combiner box, inverter input, control panel | Determines AC or DC SPD direction. |
| System voltage | 230/400V AC, 480V AC, 1000V DC, 1500V DC | Determines Uc or Ucpv selection. |
| Installation position | Main panel, sub-panel, combiner box, inverter side, terminal equipment | Determines Type 1, Type 2, Type 1+2 or Type 3 direction. |
| Earthing system | TT, TN-S, TN-C, IT | Determines wiring mode and pole arrangement. |
| Lightning exposure | External LPS, overhead line, exposed PV field, industrial site | Helps judge whether Type 1 or Type 1+2 is required. |
| Required certification | IEC, CE, TUV, UL, project approval | Prevents mismatch between product and market requirement. |
| Panel or OEM requirement | DIN rail width, remote signal, cartridge, private label, packaging | Important for OEM electrical assemblies and distributor sourcing. |
Choose the next page by your application
This SPD selection guide gives the decision framework. Use these pages for application-specific details and product direction.
LEEYEE support for SPD selection and sourcing
LEEYEE supplies surge protective devices for solar PV, distribution boards, industrial control panels, telecom, low-voltage systems and OEM electrical assemblies.
AC and DC SPD coverage
Support for AC Type 1, Type 2, Type 1+2 and PV DC SPD options for 1000V and 1500V solar systems.
OEM and distributor support
Pluggable modules, DIN rail design, remote signal contacts, private label, packaging and model selection support.
Clear selection communication
We help buyers confirm system voltage, circuit type, SPD type, poles, standard, backup protection and application match before ordering.
SPD selection guide FAQ
Short answers for buyers who need to choose the right surge protective device quickly.
How do I choose the right SPD?
Choose the right SPD by first identifying whether the protected circuit is AC or DC. Then select the SPD type by installation position, match Uc or Ucpv to the system voltage, check Iimp, In, Imax and Up, confirm poles and earthing system, and verify backup protection and applicable standard.
What is the first step in SPD selection?
The first step is to confirm whether the protected circuit is AC or DC. AC SPDs and DC SPDs are not interchangeable. PV DC systems should use DC SPDs designed for photovoltaic applications.
What is the difference between Type 1 and Type 2 SPD?
Type 1 SPD is typically used at the main incoming position or service entrance where lightning current duty may be required. Type 2 SPD is commonly used in distribution boards and sub-panels for secondary surge protection.
When should I choose Type 1+2 SPD?
Choose Type 1+2 SPD when the installation needs both lightning current capability and secondary surge protection in one device, such as main panels, lightning-exposed industrial sites, or solar PV systems with higher lightning risk.
Can I use an AC SPD on the DC side of a solar PV system?
No. The DC side of a solar PV system should use a DC SPD designed for photovoltaic applications. Selection should be based on Ucpv, PV system voltage, polarity, Type 2 or Type 1+2 requirement, and the correct DC-side standard.
What SPD should I choose for a 1500V solar system?
For a 1500V solar PV system, choose a PV-rated 1500V DC SPD. Confirm Ucpv, installation position, Type 2 or Type 1+2 requirement, In, Imax, Iimp if required, and DC disconnection design.
Is higher Imax always better?
Not always. Imax is only one comparison parameter. A suitable SPD must also match AC/DC circuit type, voltage rating, SPD type, Up, poles, earthing system, backup protection, installation position and standard requirement.
Do SPDs need backup fuses or circuit breakers?
Many SPD installations require backup overcurrent protection. The correct fuse or circuit breaker must follow the SPD datasheet, available short-circuit current and installation standard.
What information should I send to an SPD supplier?
Send the system type, AC or DC side, system voltage, installation position, earthing system, lightning exposure, required certification, pole number, monitoring requirement and quantity.
Need help selecting the right SPD?
Send us your system voltage, AC/DC circuit, installation position, earthing system, lightning exposure and required standard. LEEYEE can help match a suitable SPD direction for solar PV, distribution boards, industrial cabinets and OEM assemblies.