Quick Answer: How Do You Choose a DC SPD for Solar?
Choose a DC SPD for solar by confirming five items first: the PV string maximum open-circuit voltage, whether the installation needs Type 2 or Type 1+2 protection, where the SPD will be installed, how short the SPD connection leads can be kept, and which standard or project specification applies.
For most rooftop and commercial PV systems, the selection path looks like this:
| Decision | Practical answer |
|---|---|
| What device is needed on the PV side? | A PV DC-rated SPD, not an AC SPD |
| Which voltage rating matters most? | Ucpv, selected above the maximum cold-weather PV string Voc |
| Type 2 or Type 1+2? | Type 2 for many induced-surge applications; Type 1+2 where lightning-current exposure is higher |
| Where is it installed? | Combiner box, inverter DC input, or both ends of a long DC cable route |
| Which standards matter? | IEC 61643-31 and IEC 61643-32 for PV DC SPDs; IEC 61643-11 for AC-side SPDs |
| What installation detail is often missed? | Short, direct SPD leads to reduce inductive voltage rise during a surge |
A DC SPD for solar is a surge protective device installed on the direct-current side of a photovoltaic system. Its job is to limit transient overvoltage caused by lightning-induced surges, switching events, or long outdoor cable runs before that voltage reaches the inverter, combiner box electronics, monitoring equipment, or other DC-side components.
In a solar PV system, surge protection is not just an accessory at the AC distribution board. PV strings are often installed on roofs, open ground, elevated frames, or long cable routes. Those DC conductors can pick up induced surge energy during nearby lightning activity even when the array is not directly struck. That is why a complete solar protection design normally considers DC SPD placement, AC SPD placement, cable routing, bonding, grounding, and the withstand level of the inverter.
For VIOX buyers and panel builders, the practical question is simple: which surge protective device should be selected for the PV DC side, and where should it be installed?
What Is SPD in a Solar System?
SPD means surge protective device. In a solar system, an SPD limits short-duration voltage spikes by diverting surge current toward the protective earth or equipotential bonding system. It does not replace fuses, circuit breakers, isolators, or proper grounding. It works together with them.
In photovoltaic systems, SPDs are usually divided by location:
| SPD location | Typical role | Typical device type |
|---|---|---|
| PV array or string combiner box | Limits surge energy picked up by outdoor DC string cables | DC SPD, usually Type 2 or Type 1+2 depending on lightning exposure |
| Inverter DC input | Protects the inverter from DC-side surges entering from the PV array | DC SPD |
| Inverter AC output or AC distribution board | Limits AC-side surge entering from grid or distribution wiring | AC SPD |
| Monitoring and communication lines | Protects data cables, RS485, Ethernet, sensors, or monitoring interfaces | Signal/data SPD matched to the signal type |
The most important rule is that the SPD must match the circuit it protects. A DC PV input needs a DC PV-rated SPD. An AC distribution board needs an AC SPD.
DC SPD vs AC SPD for Solar: What Is the Difference?
A solar installation may need both DC and AC surge protection, but the devices are not interchangeable.
| Comparison point | DC SPD for solar PV | AC SPD for solar output/grid side |
|---|---|---|
| Installed on | PV strings, combiner boxes, inverter DC input | Inverter AC output, AC distribution board, main panel |
| Main voltage parameter | Ucpv or PV DC maximum continuous operating voltage | Uc or MCOV for AC system voltage |
| Typical standard direction | IEC 61643-31 for SPDs connected to the DC side of PV installations; IEC 61643-32 for selection/application guidance | IEC 61643-11 for low-voltage AC SPDs |
| Arc and disconnection issue | DC arc behavior is more demanding because DC has no natural zero crossing | AC current crosses zero every cycle, changing interruption behavior |
| Common mistake | Using an AC SPD on the PV DC side | Assuming AC-side SPD alone protects the PV array and inverter DC input |
If the system has PV strings feeding an inverter, the AC-side SPD at the distribution board does not fully protect the inverter from surges entering through the DC input. DC-side protection should be evaluated separately.
Type 2 vs Type 1+2 DC SPD: Which One Do You Need?
Most solar buyers first ask whether they need a Type 2 DC SPD or a Type 1+2 DC SPD. The answer depends on lightning exposure, system layout, the presence of an external lightning protection system, cable routing, and project requirements.
| Solar PV condition | Recommended starting point | Why it matters |
|---|---|---|
| Residential rooftop PV without external lightning protection and moderate exposure | Type 2 DC SPD | Protects against induced surges and switching transients |
| Commercial rooftop PV with long DC cable runs | Type 2 DC SPD at key DC entry points; consider multiple locations | Cable length increases induced surge risk and loop area |
| PV array on exposed ground mount, hilltop, open field, or high lightning area | Type 1+2 DC SPD may be required by design risk assessment | Higher probability of partial lightning current entering the system |
| Building has an external lightning protection system and separation distance cannot be maintained | Type 1+2 DC SPD is commonly selected | The PV system may be exposed to lightning current components |
| Utility-scale or high-value inverter station | Coordinated Type 1+2 and Type 2 protection strategy | Downtime and replacement cost justify layered protection |
For a broader explanation of Type 1, Type 2, and Type 3 device roles, see VIOX’s guide to SPD Type 1 vs Type 2 vs Type 3.
Engineering Note: Type Is Not the Same as Voltage Rating
A Type 2 DC SPD is not automatically suitable for every PV system. It still needs the correct Ucpv, pole configuration, short-circuit behavior, and installation method. A 600V PV array, a 1000V PV array, and a 1500V PV array require different voltage checks even if all three projects use Type 2 protection.
How to Select Ucpv for a Solar DC SPD
The most important voltage parameter for a PV DC SPD is Ucpv, often described as the maximum continuous operating voltage for photovoltaic DC applications. The SPD must remain stable during the highest normal open-circuit voltage of the PV array, including cold-weather voltage rise.
Do not select the DC SPD only from the inverter’s nominal DC voltage. Start from the PV string maximum open-circuit voltage.
Use this concept:
Voc_max = Nseries x Voc_module_STC x [1 + |betaVoc| x (25 - Tmin)]
Where:
- Nseries = number of modules connected in series per string
- Voc_module_STC = module open-circuit voltage at standard test conditions
- betaVoc = module Voc temperature coefficient per degree Celsius, converted to decimal form
- Tmin = minimum expected cell or ambient design temperature, depending on the project calculation method
Then choose a DC SPD with a Ucpv rating above the calculated maximum PV string voltage, following the SPD datasheet and the project standard.
| PV system class | Typical DC SPD voltage shortlist | Selection caution |
|---|---|---|
| 600V PV system | 600V or suitable higher Ucpv class | Confirm cold-weather Voc does not exceed SPD rating |
| 1000V PV system | 1000V or suitable higher Ucpv class | Check string length and module temperature coefficient |
| 1500V PV system | 1500V PV DC SPD class | Confirm the device is specifically intended for 1500V PV DC duty |
VIOX’s SPD product range includes DC SPD families for common PV voltage classes, including 500V, 600V, 800V, 1000V, 1200V, and 1500V options on the VIOX SPD product page. The final model should still be matched against the actual PV string voltage, project standard, and installation environment.
Worked Example: Choosing Ucpv for a Cold-Weather PV String
Assume a PV string has a total open-circuit voltage of 900V at standard test conditions. The module Voc temperature coefficient is -0.3% per degree Celsius, and the minimum design temperature is -10°C.
The temperature difference from 25°C is:
25 - (-10) = 35°C
The cold-weather voltage rise is:
900V x 0.003 x 35 = 94.5V
The estimated maximum string open-circuit voltage is:
900V + 94.5V = 994.5V
In this case, a 1000V Ucpv SPD may be too close to the calculated maximum, depending on the datasheet tolerance, project margin, and local design rules. A 1200V PV DC SPD would often be the more practical shortlist, subject to inverter and project specification review.
This example is intentionally simplified. Real projects should use the module datasheet, inverter limits, local temperature data, and the applicable design standard.
Solar DC SPD Selection by System Type
Different PV projects do not need the same surge protection layout. A small residential rooftop system, a commercial rooftop with long DC cable trays, and a utility-scale inverter station have different exposure levels and maintenance expectations.
| PV system type | Typical DC-side SPD approach | What to verify |
|---|---|---|
| Residential rooftop PV | Type 2 DC SPD near inverter DC input or in a nearby small combiner | Ucpv, inverter manual, local code, AC-side SPD requirement |
| Commercial rooftop PV | Type 2 DC SPD in combiner boxes and/or near inverter inputs | Cable route length, bonding, rooftop lightning exposure, enclosure condition |
| Ground-mounted PV array | Type 2 or Type 1+2 depending on exposure and lightning risk | Distance to inverter, site lightning density, grounding grid, long outdoor cable loops |
| PV system with external lightning protection system | Type 1+2 DC SPD is commonly evaluated at DC entry points | Separation distance, bonding, IEC 62305 lightning protection concept, project specification |
| Utility-scale inverter station | Layered protection across array/combiner, inverter DC input, and AC output | Coordination, monitoring, remote indication, spare cartridges, maintenance access |
| PV plus battery energy storage | DC SPD strategy should be reviewed separately for PV side, battery side, and inverter/converter side | DC voltage class, fault current, device compatibility, BESS supplier requirements |
The purpose of this table is not to replace engineering design. It helps buyers ask better RFQ questions before selecting a specific DC SPD model.
DC SPD Connection Diagram for Solar PV Systems
A correct solar DC SPD connection diagram should show one key idea clearly: the SPD is connected in parallel with the PV DC circuit, not in series with the load current path.
The PV string current flows through the normal DC circuit toward the inverter. The SPD provides a surge-diversion path from the DC conductors to protective earth or the bonding system when transient overvoltage appears.
| Diagram element | Correct representation | Common mistake |
|---|---|---|
| PV+ and PV- conductors | Continue through DC protection and isolation toward inverter input | Drawing the SPD as if it carries normal string current in series |
| DC SPD | Connected between PV conductors and PE/bonding according to system configuration | Connecting only one pole where the system requires multi-pole protection |
| Protective earth or bonding bar | Shown as a short, low-impedance path near the SPD | Long green/yellow lead routed around the enclosure for neatness |
| Combiner box or inverter DC input | Shown as the physical installation point | Placing the SPD far away from the protected equipment |
| AC SPD | Shown separately on inverter output or AC board | Assuming one AC SPD protects the whole PV DC side |
For a typical PV system, the diagram should normally show these protection layers:
- PV strings enter a solar combiner box.
- The combiner box includes DC fuses or DC breakers where required, a DC isolator or switch-disconnector, and a DC SPD.
- The combined DC output runs to the inverter DC input.
- If the DC run is long, another DC SPD is installed near the inverter input.
- The inverter AC output is protected separately with a suitable AC SPD at the AC distribution board or inverter output panel.
Where to Install DC SPD in a Solar System
SPD placement is as important as SPD selection. A correctly rated SPD with poor location or long leads may still allow high residual voltage to reach the inverter.
| Installation point | When it is used | Practical selection note |
|---|---|---|
| Inside the PV combiner box | Multi-string systems, outdoor array junction point, long cable runs | Often the best location for array-side DC surge control |
| Near inverter DC input | Protecting inverter electronics from incoming PV DC surges | Especially important when inverter is far from the array |
| At both array/combiner and inverter ends | Long DC cable distance between array and inverter | Helps limit surge voltage at both ends of the cable |
| AC distribution board | Grid-side or inverter output surge protection | Requires AC SPD, not DC SPD |
| Communication cabinet or monitoring interface | Data lines, remote monitoring, RS485, Ethernet, sensors | Needs signal SPD matched to data line type |
The existing PV protection layout may also include DC MCBs and a DC isolator switch. These devices perform different jobs from the SPD. The DC MCB protects against overcurrent in the correct application context, the isolator provides switching/isolation, and the SPD limits transient overvoltage.
The 10-Meter Rule: When One DC SPD Is Not Enough
In many PV designs, the distance between the PV array and the inverter determines whether a single DC SPD location is enough. A common design rule is:
- If the DC cable distance between the array and inverter is short, one DC SPD near the inverter input or in the nearby combiner may be sufficient, depending on the system layout.
- If the DC cable route is longer than about 10 meters, protection at both ends should be considered: one SPD near the PV array or combiner box, and another near the inverter DC input.
The reason is not only distance. Long outdoor cables can pick up induced surge voltage, and a surge entering at one end may still create damaging voltage at the other end if the protection point is too far away.
For EPC and panel-building work, treat the 10-meter rule as a design checkpoint, not a substitute for project standards, lightning risk assessment, or inverter manufacturer requirements.
Keep DC SPD Lead Length Short
SPD wiring is a high-frequency surge path. During a fast surge, every extra centimeter of conductor adds inductive voltage drop. The basic physics is:
V = L x di/dt
Where:
- V is the inductive voltage rise added by the lead
- L is the wiring inductance
- di/dt is the surge current rate of rise
This is why a beautifully routed SPD cable can perform badly if it forms a long loop around the enclosure. In IEC-based installation practice, the total connection length around the SPD protection path is commonly kept as short as possible, with 0.5m often used as a key target for effective SPD connections.
Practical installation guidance:
- Mount the SPD close to the conductors and bonding bar it protects.
- Avoid long loops between the SPD and PE/bonding conductor.
- Avoid sharp bends where possible.
- Keep positive, negative, and bonding paths compact and direct.
- Use conductor sizes and backup protection as required by the SPD manufacturer and applicable code.
How to Choose DC SPD Ratings for Solar
When comparing DC SPD datasheets, do not choose by one number alone. The selection should consider voltage, surge-current capability, protection level, short-circuit behavior, and maintenance visibility.
| Parameter | What it means | Why it matters in solar PV |
|---|---|---|
| Ucpv | Maximum continuous operating voltage for PV DC use | Must exceed the maximum PV open-circuit voltage under cold conditions |
| In | Nominal discharge current, usually for repeated surge events | Indicates durability under repeated induced surges |
| Imax | Maximum discharge current for Type 2 SPD test context | Helps compare peak surge handling within the same device category |
| Iimp | Impulse current for Type 1 or Type 1+2 devices | Relevant where partial lightning current may be present |
| Up | Voltage protection level | Lower Up generally means lower let-through voltage, but must be evaluated with coordination and installation lead length |
| Iscpv / SCCR direction | Short-circuit behavior or current withstand with required backup protection | Critical because PV DC fault current and disconnection behavior differ from AC systems |
| Pole configuration | 2P, 3P, or application-specific PV configuration | Must match grounded, ungrounded, or system-specific PV DC wiring |
| Status indication | Visual indicator and optional remote signaling | Helps maintenance teams know when the SPD cartridge has reached end of life |
Do Not Compare kA Ratings Without Context
It is tempting to choose the largest kA number on a product page. That is not always the best selection method. A higher surge-current rating can be useful, but only when the device also matches Ucpv, Up, short-circuit requirements, type classification, installation location, and coordination with upstream/downstream protection.
Type 1+2 DC SPD for Solar: When It Makes Sense
A Type 1+2 DC SPD combines lightning-current and surge-limiting characteristics in one device family. In PV projects, it is most relevant when the DC side may be exposed to higher surge energy.
Consider Type 1+2 DC SPD when:
- The building has an external lightning protection system.
- PV array wiring cannot maintain adequate separation from the lightning protection system.
- The array is installed in an exposed open-field or hilltop location.
- The site has high lightning density or high downtime cost.
- The project specification calls for lightning-current capable SPD protection.
Use Type 2 DC SPD when:
- The project mainly needs protection against induced surges and switching transients.
- There is no external lightning protection system affecting the PV array.
- The inverter manufacturer or project design specifies Type 2 DC surge protection.
- Protection is being added inside a combiner box or inverter-side DC board for standard rooftop/commercial PV protection.
IEC 61643-31 and IEC 61643-32: What Standards Matter?
For solar PV DC surge protection, the key IEC direction is the IEC 61643 series:
- IEC 61643-31 covers requirements and test methods for SPDs connected to the DC side of photovoltaic installations.
- IEC 61643-32 provides selection and application principles for SPDs connected to the DC side of PV installations.
- IEC 61643-11 applies to SPDs connected to low-voltage AC power systems.
This distinction matters because a solar PV DC SPD is not simply an AC SPD with a different label. The test context, voltage behavior, disconnection requirements, and application risks differ.
For North American projects, UL 1449 and local electrical code requirements may also be relevant. For any market, the project engineer should confirm the exact standard edition, local adoption, inverter manual requirements, and authority having jurisdiction requirements.
Documents to Request Before Approving a Solar DC SPD
For B2B procurement, the safest question is not only “what is the price?” It is “what documentation proves this SPD fits the PV DC application?”
| Document or evidence | Why it matters |
|---|---|
| DC SPD datasheet | Confirms Ucpv, In, Imax, Iimp if applicable, Up, pole configuration, and connection method |
| IEC 61643-31 test or compliance documentation | Helps verify the device is intended for PV DC surge protection, not only AC low-voltage SPD use |
| Wiring diagram from manufacturer | Prevents incorrect pole connection, wrong PE routing, and unsuitable earthing configuration |
| Backup protection instruction | Confirms whether an upstream fuse, DC MCB, or other protection is required |
| End-of-life indication description | Confirms visual window, pluggable cartridge behavior, and optional remote contact |
| Environmental and enclosure guidance | Important for outdoor combiner boxes, high heat, humidity, coastal sites, and condensation risk |
If the supplier cannot clearly state whether the product is for PV DC use, the buyer should not treat it as a solar DC SPD.
Common Solar SPD Installation Mistakes
Mistake 1: Using an AC SPD on the DC Side
This is the most dangerous selection error. PV DC circuits require PV DC-rated surge protection. An AC SPD may not safely handle the voltage and DC interruption behavior of a photovoltaic circuit.
Mistake 2: Choosing Ucpv Too Low
Cold weather raises PV open-circuit voltage. If the SPD voltage rating is selected from nominal system voltage instead of calculated maximum Voc, the SPD may be stressed during normal operation.
Mistake 3: Protecting Only the AC Side
An AC SPD at the distribution board is useful, but it does not remove the need to evaluate DC-side surge exposure. Inverter DC inputs are often the most expensive electronics directly connected to long outdoor PV cables.
Mistake 4: Installing the SPD Too Far from the Protected Equipment
A long cable between the SPD and inverter input reduces protection quality. The SPD should be placed close to the equipment or cable entry point it protects.
Mistake 5: Long Leads and Large Wiring Loops
SPD leads are not normal low-frequency power wiring during a surge. Long leads add inductive voltage. Keep the surge path short, direct, and compact.
Mistake 6: Ignoring Remote Status Signals
In commercial PV plants, a failed SPD cartridge can remain unnoticed if the device only has a visual indicator inside a closed box. Remote signaling contacts can help maintenance teams identify end-of-life status without waiting for the next manual inspection.
Mistake 7: Poor Outdoor Enclosure Design
Outdoor combiner boxes face heat, ultraviolet exposure, humidity, and condensation. A DC SPD installed in a poorly designed enclosure may age faster, even if the SPD rating itself looks correct. For outdoor solar cabinets, check enclosure rating, thermal conditions, cable gland sealing, condensation control, and maintenance access.
DC SPD Selection Checklist for Solar Buyers
Use this checklist before requesting price or approving a PV SPD design.
| Check item | What to confirm |
|---|---|
| PV system voltage | 600V, 1000V, 1200V, 1500V, or project-specific DC class |
| Maximum PV string Voc | Include cold-temperature correction, not only nominal voltage |
| SPD type | Type 2 or Type 1+2 based on lightning exposure and project design |
| Installation point | Combiner box, inverter DC input, both ends, or AC output |
| DC vs AC side | DC SPD for PV input; AC SPD for inverter output or grid side |
| Ucpv | Must be suitable for the calculated PV maximum DC voltage |
| Up | Must coordinate with protected equipment withstand level and lead length |
| In / Imax / Iimp | Match exposure level, type classification, and project specification |
| Short-circuit behavior | Confirm backup protection or Iscpv/SCCR requirements from datasheet |
| Pole configuration | Match grounded, floating, or system-specific PV wiring |
| Status indication | Visual indicator, replaceable cartridge, remote contact if needed |
| Standards | IEC 61643-31/32, UL 1449, or local requirement depending on market |
Recommended PV SPD Specification Format
For clearer RFQs, do not write only “solar SPD price.” Send a specification that includes the real design conditions.
Example RFQ format:
| RFQ field | Example input |
|---|---|
| Application | Rooftop PV / ground-mounted PV / commercial inverter station |
| PV system voltage | 1000V DC or 1500V DC |
| Maximum string Voc | Calculated value under minimum temperature |
| SPD type | Type 2 DC SPD or Type 1+2 DC SPD |
| Installation point | Combiner box and/or inverter DC input |
| Pole configuration | 2P, 3P, or project-specific |
| Required standard direction | IEC 61643-31, UL 1449, or local requirement |
| Status monitoring | Visual only or remote signaling contact |
| Enclosure condition | Indoor inverter room, outdoor combiner box, coastal site, high heat |
This format helps VIOX or any qualified supplier shortlist the correct DC SPD family instead of quoting a device that only matches one keyword.
FAQ
Can one SPD protect both the PV DC side and the AC output side?
No. A DC SPD protects the PV input side, while an AC SPD protects the inverter output or grid/distribution side. A complete solar surge protection design often evaluates both sides because surge energy can enter through outdoor PV cables or through the AC distribution network.
How do I know whether to install one DC SPD or two DC SPDs?
Check the distance between the PV array or combiner box and the inverter. If the DC cable run is short, one properly placed DC SPD may be enough depending on the system design. If the DC cable route is long, commonly around 10 meters or more, engineers often evaluate SPDs at both ends: one near the array or combiner and one near the inverter DC input.
What happens if Ucpv is lower than the real PV string voltage?
The SPD may treat normal PV operating voltage as an overvoltage condition. This can cause overheating, premature end-of-life operation, nuisance failure indication, or a dangerous failure mode. Ucpv should be selected above the maximum cold-weather open-circuit voltage of the PV string, not just above the nominal inverter voltage.
Why does lead length matter if the SPD has a low Up value?
The SPD datasheet Up value is measured under standardized test conditions. In the real cabinet, long leads add inductive voltage during a fast surge. The effective let-through voltage at the inverter can be higher than the SPD’s marked Up if the wiring path is long, looped, or poorly bonded.
Is Type 1+2 DC SPD always better than Type 2 DC SPD?
Not always. Type 1+2 is useful where lightning-current exposure is expected, such as systems with external lightning protection or highly exposed arrays. For many standard rooftop or commercial PV systems where induced surges are the main concern, a correctly selected Type 2 DC SPD may be the appropriate choice. The decision should follow the project lightning risk and local design requirements.
Should the DC SPD be installed before or after the DC isolator?
The exact position depends on the combiner box or inverter input design and the manufacturer’s wiring diagram. The important point is that the SPD must be connected close to the protected conductors and bonding bar with short leads. It should not be placed far away simply because it is more convenient for cabinet layout.
What remote signal should a solar DC SPD provide for commercial PV systems?
Commercial and utility PV systems often use SPDs with a visual status window plus an optional remote signaling contact, typically wired to a monitoring system, alarm circuit, or supervisory control system. This helps maintenance teams detect an end-of-life SPD without opening every combiner box manually.
Can a solar DC SPD protect the inverter if the combiner box is far away?
Only partially. If the combiner box is far from the inverter, the cable between them can still pick up induced surge voltage. In that case, a second DC SPD near the inverter DC input may be needed to reduce the surge voltage reaching the inverter.
What documents should I request from a DC SPD supplier before using it in a PV combiner box?
Ask for the DC SPD datasheet, wiring diagram, Ucpv rating, In/Imax or Iimp ratings, Up value, backup protection instructions, end-of-life indication details, and IEC 61643-31-related test or compliance documentation where applicable. For outdoor combiner boxes, also confirm environmental and enclosure requirements.
Does a DC SPD replace PV fuses, DC MCBs, or DC isolator switches?
No. A DC SPD limits transient overvoltage. PV fuses or DC MCBs protect against overcurrent where applicable, and DC isolator switches provide switching or isolation. These devices perform different functions and should be coordinated in the combiner box or inverter input design.
Conclusion
The best DC SPD for solar is not chosen by the largest kA number alone. It is chosen by matching the PV DC voltage, Type 2 or Type 1+2 role, installation location, cable length, lead length, grounding/bonding design, and relevant standards such as IEC 61643-31 and IEC 61643-32.
For most buyers, the correct evaluation sequence is:
- Confirm whether the protection point is DC side or AC side.
- Calculate the maximum PV string Voc under cold conditions.
- Select a suitable Ucpv class.
- Decide between Type 2 and Type 1+2 based on lightning exposure.
- Place the SPD close to the protected equipment and keep leads short.
- Confirm backup protection, status indication, and enclosure environment.
If you are selecting DC SPD products for PV combiner boxes, inverter input protection, or solar distribution panels, VIOX can help match the right SPD family to the actual voltage class, installation point, and project requirement.
