{"id":1855,"date":"2026-07-27T22:15:02","date_gmt":"2026-07-27T14:15:02","guid":{"rendered":"https:\/\/jutrion.com\/?p=1855"},"modified":"2026-07-27T22:25:59","modified_gmt":"2026-07-27T14:25:59","slug":"como-seleccionar-dc-spd-solar-pv","status":"publish","type":"post","link":"https:\/\/jutrion.com\/es\/how-to-select-dc-spd-solar-pv\/","title":{"rendered":"How to Select a DC SPD for Solar PV: Type, Sizing, and Standards"},"content":{"rendered":"
\"\"<\/figure>\n\n\n\n
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Fast answer: how to specify a DC SPD for a solar array<\/strong><\/p>\n<\/blockquote>\n\n\n\n

Choose a DC SPD by four inputs: the array’s maximum open-circuit voltage, its maximum short-circuit current, whether a lightning protection system is present, and the earthing arrangement. Size the maximum continuous operating voltage to Ucpv \u2265 1.2 \u00d7 the array’s maximum Voc<\/strong> (IEC 61643-32), pick Type 2<\/strong> for ordinary rooftops or Type 1+2<\/strong> where lightning exposure or an LPS is present, and confirm the device is DC-rated with an integrated thermal disconnector. Match the voltage class to the system: 600 V, 1000 V, or 1500 V.<\/p>\n\n\n\n

A DC surge protective device fails in a way an AC one never does. On a cold, clear morning a photovoltaic string sits at its highest voltage of the year, the array is live the instant the sun clears the horizon, and there is no alternating zero-crossing to help extinguish an internal arc. An SPD chosen against the nominal system voltage \u2014 “it’s a 1000 V system, so a 1000 V device is fine” \u2014 can sit permanently overstressed, drift into leakage, and trip its thermal disconnector months before its rated life. The number that protects the array is not the nominal voltage; it is the array’s real maximum open-circuit voltage plus a margin, and everything else in the specification follows from getting that one figure right.<\/p>\n\n\n\n

This guide works through the DC-side selection the way a panel builder or EPC specifier actually does it: establish the array inputs, size the voltage, choose the type, set the protective ratings, then close the loop on fault current, the thermal disconnector, configuration, earthing, the datasheet, the AC side, and lifecycle. It follows the framework of IEC 61643-31 (the product standard for PV DC SPDs) and IEC 61643-32 (selection and application). For the wider view across Type 1, 2, and 3 devices and both AC and DC sides, see the complete surge protective device guide<\/a>; this article is the DC-side companion that goes deep where a solar array makes the decision different.<\/p>\n\n\n\n

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Why a DC SPD is not an AC SPD turned sideways<\/h2>\n<\/blockquote>\n\n\n\n

The temptation to reuse a spare AC surge arrester on the PV side is the single most dangerous shortcut in solar surge protection. Alternating current passes through zero one hundred times a second; when a varistor at end of life begins to conduct, that natural current-zero helps the internal disconnector clear the follow current. A photovoltaic array delivers continuous direct current with no zero-crossing at all. A degrading metal-oxide varistor can therefore sustain a DC arc, heat, and become a fire source rather than fail safe.<\/p>\n\n\n\n

The protective element itself works the same way in both worlds: a metal-oxide varistor (MOV) is effectively an open circuit at normal voltage and collapses to a low impedance within nanoseconds when the voltage crosses its threshold, diverting the surge to earth and clamping the let-through voltage. Some devices pair the MOV with a gas discharge tube (GDT) in series to eliminate leakage current and improve the failure mode. What changes on the DC side is not the clamping physics but the fault behaviour after the element ages, and that is why the whole device \u2014 its voltage rating, its disconnector, and its internal topology \u2014 is built for DC.<\/p>\n\n\n\n

For that reason a compliant PV DC SPD is built differently. It is rated for continuous DC operation, its modes of protection are arranged for a floating or functionally earthed DC array rather than a neutral-referenced AC supply, and it carries an integrated thermal disconnector<\/strong> that isolates the varistor on failure without relying on a current-zero. IEC 61643-31 is explicit that these devices are dedicated to the DC side of PV generators and inverters \u2014 an AC SPD does not meet those requirements and must never substitute. This is a different job from a device that guards against sustained mains over- and under-voltage; if your concern is a slow rise or sag in supply voltage rather than a microsecond transient, that is the domain of an over- and under-voltage protector<\/a>, not an SPD.<\/p>\n\n\n\n

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Start with the array: the four inputs that decide the SPD<\/h3>\n<\/blockquote>\n\n\n\n
\"\"<\/figure>\n\n\n\n

Every rating on the SPD datasheet answers a question about the array. Establish these four inputs before you look at any product:<\/p>\n\n\n\n

    \n
  • Maximum open-circuit voltage, Uoc(max).<\/strong> Not the nominal system voltage \u2014 the highest voltage the string can reach, which occurs at open circuit on the coldest expected morning. This sets Ucpv.<\/li>\n\n\n\n
  • Maximum short-circuit current, Iscpv.<\/strong> The array’s prospective short-circuit current at the SPD’s position, enhanced for irradiance and temperature. This sets the short-circuit withstand requirement and decides whether an external backup device is needed.<\/li>\n\n\n\n
  • Lightning exposure and LPS presence.<\/strong> Whether the site has a lightning protection system, sits in an exposed or high-flash-density location, or cannot maintain separation distance from down-conductors. This decides Type 2 versus Type 1+2.<\/li>\n\n\n\n
  • Earthing arrangement and DC cable length.<\/strong> Functionally earthed or floating array, and the cable distance between array and inverter. This decides the SPD’s internal configuration and how many SPD locations the system needs.<\/li>\n<\/ul>\n\n\n\n

    Get these four right and the rest of the specification is mechanical. Guess at them and no amount of headline discharge-current rating will save the install.<\/p>\n\n\n\n

    \n

    Sizing Ucpv: the 1.2 \u00d7 Voc rule and the cold-morning check<\/h3>\n<\/blockquote>\n\n\n\n

    Ucpv<\/strong> is the maximum continuous operating voltage the SPD can withstand indefinitely without degrading. Every mode of protection inside the device \u2014 positive-to-earth, negative-to-earth, and pole-to-pole \u2014 must ride above the array’s highest voltage under all service conditions. IEC 61643-32 states the rule directly:<\/p>\n\n\n\n

    Ucpv \u2265 1.2 \u00d7 Uoc(max)<\/strong>, where Uoc(max) is the array’s maximum open-circuit voltage at standard test conditions.<\/p>\n\n\n\n

    The 1.2 factor is not arbitrary padding. Open-circuit voltage rises as cell temperature falls below the 25\u00a0\u00b0C of standard test conditions, at roughly 0.3\u00a0% per degree for crystalline silicon. The 20\u00a0% margin absorbs that cold-weather rise for most climates so the SPD is never operated at or above its Ucpv when the array peaks at dawn.<\/p>\n\n\n\n

    \n

    Worked example: a 1500 V-class string<\/h3>\n<\/blockquote>\n\n\n\n
    \"\"<\/figure>\n\n\n\n

    Take a string of 24 modules, each with an STC open-circuit voltage of 49.5 V.<\/p>\n\n\n\n

      \n
    1. Array Uoc(max) at STC = 24 \u00d7 49.5 V = 1188 V<\/strong>.<\/li>\n\n\n\n
    2. Apply the standard margin: Ucpv \u2265 1.2 \u00d7 1188 V = 1426 V<\/strong>.<\/li>\n\n\n\n
    3. Select the next voltage class above that figure: a 1500 V DC SPD<\/strong> (Ucpv rated at 1500 V).<\/li>\n<\/ol>\n\n\n\n

      Cross-check the cold morning for an extreme site. At a design minimum cell temperature of \u221210\u00a0\u00b0C, the temperature term is a 35-degree drop \u00d7 0.3\u00a0%\/\u00b0C \u2248 +10.5\u00a0%, so Voc rises to about 1188 \u00d7 1.105 \u2248 1313 V<\/strong> \u2014 still comfortably below the 1500 V Ucpv. For a very cold climate, compute Voc at your own design minimum temperature with the module’s temperature coefficient and confirm Ucpv still clears it; the 1.2 factor covers ordinary conditions, not an Arctic install. Then map to the class shortlist:<\/p>\n\n\n\n

        \n
      • Systems up to ~600 V \u2192 600 V (or higher) Ucpv class.<\/li>\n\n\n\n
      • 1000 V systems \u2192 1000 V class.<\/li>\n\n\n\n
      • 1500 V systems \u2192 1500 V class.<\/li>\n<\/ul>\n\n\n\n
        \n

        Type 2 or Type 1+2? Match the SPD to lightning exposure<\/h3>\n<\/blockquote>\n\n\n\n

        The type is a lightning-risk decision, not a quality tier. It follows from the fourth input above and from the site’s lightning protection design.<\/p>\n\n\n\n

          \n
        • Type 2<\/strong> devices are tested with the 8\/20\u00a0\u00b5s waveform and rated by nominal discharge current (In) and maximum discharge current (Imax). They handle induced surges and switching transients \u2014 the everyday threat on a building rooftop with no external lightning protection system. This covers the majority of residential and commercial rooftop arrays.<\/li>\n\n\n\n
        • Type 1+2<\/strong> devices add a partial-lightning-current rating, the impulse current Iimp tested with the 10\/350\u00a0\u00b5s waveform, while still providing Type 2 protection. Specify them where a lightning protection system is present and separation distance cannot be maintained, on exposed ground-mount and hilltop arrays, and in high lightning-flash-density regions \u2014 anywhere a share of direct lightning current can be conducted into the DC side.<\/li>\n<\/ul>\n\n\n\n

          The deciding question is whether direct or partial lightning current can reach the array wiring, which is assessed through the site’s lightning protection risk analysis (the IEC 62305 series). If the answer is yes, the extra Iimp capability of a Type 1+2 device is protecting against an energy the Type 2 test does not represent. If the answer is clearly no, a well-specified Type 2 device is the correct and more economical choice, not a compromise.<\/p>\n\n\n\n

          \n

          The DC-side ratings that actually protect the inverter<\/h3>\n<\/blockquote>\n\n\n\n

          Once voltage and type are fixed, three ratings determine whether the inverter behind the SPD is genuinely protected:<\/p>\n\n\n\n

          Rating<\/th>What it represents<\/th>Selection rule<\/th><\/tr><\/thead>
          Up<\/strong> (voltage protection level)<\/td>The let-through voltage the SPD allows to reach the equipment during a surge<\/td>Keep Up at least ~20 % below the impulse withstand voltage (Uw) of the inverter’s DC input, so a margin remains after lead-length losses<\/td><\/tr>
          In<\/strong> (nominal discharge current)<\/td>The 8\/20\u00a0\u00b5s current the SPD can divert repeatedly without damage<\/td>Higher In gives more headroom and longer service life at exposed sites; treat it as the working rating, not the maximum<\/td><\/tr>
          Imax<\/strong> (maximum discharge current)<\/td>The single-event 8\/20\u00a0\u00b5s current the SPD can survive once<\/td>A survival ceiling for a severe event, not a duty figure; specify with margin above the expected surge, not equal to it<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

          Up is the rating that most often gets ignored and most directly decides whether the inverter survives. A device with an impressive Imax but a Up that sits close to the inverter’s withstand voltage lets through a transient the electronics cannot absorb. The JUTRION solar DC range, for example, specifies Up on its 40 kA (8\/20 \u00b5s Imax) devices so this coordination can be checked against the inverter datasheet rather than assumed.<\/p>\n\n\n\n

          \n

          Coordinate the stages, and check the inverter’s built-in SPD<\/h2>\n<\/blockquote>\n\n\n\n

          Two SPD-related questions decide whether extra devices help or simply waste money.<\/p>\n\n\n\n

          Energy coordination between stages.<\/strong> When a Type 1+2 device at the array or combiner box works together with a Type 2 device at the inverter, the two must be energy-coordinated so the upstream device takes the high-energy hit and the downstream device only trims the residual. Coordination is achieved by keeping enough DC cable between the stages \u2014 roughly 10 metres provides sufficient inductive decoupling \u2014 or, where that distance is not available, by a decoupling inductor or a manufacturer-verified coordinated set. Mixing two makers’ devices with no defined decoupling can leave the downstream SPD overstressed; follow the manufacturer’s coordination data rather than assuming any two devices cooperate.<\/p>\n\n\n\n

          The inverter may already contain a DC SPD.<\/strong> Many modern string inverters ship with an integrated Type 2 DC SPD or a slot for a pluggable module. Confirm this before specifying an external device at the inverter DC input: if the inverter already protects its own terminals, the external effort belongs at the array or combiner end, where a long DC home-run is otherwise unprotected. Specifying a second SPD 200\u00a0mm from an existing integrated one protects nothing new and adds a failure point.<\/p>\n\n\n\n

          \n

          Fault current, backup, and the thermal disconnector: the safety chain competitors skip<\/h2>\n<\/blockquote>\n\n\n\n

          This is where a spec-grade selection separates from a catalogue pick, and where most solar SPD articles go quiet. Three linked requirements keep a failing SPD from becoming a DC fault.<\/p>\n\n\n\n

          Short-circuit withstand (Iscpv \/ SCCR)<\/h3>\n\n\n\n

          The SPD must survive the array’s prospective short-circuit current at its installed position. Compare the device’s rated short-circuit withstand current, Iscpv, against the array’s maximum short-circuit current \u2014 approximately 1.25 \u00d7 the modules’ STC Isc for the relevant number of parallel strings, the 1.25 factor covering irradiance and temperature enhancement per PV array design practice (IEC 62548). For a combiner box gathering four parallel strings of modules rated 13.5 A STC short-circuit current, that is 1.25 \u00d7 13.5 A \u00d7 4 \u2248 68 A<\/strong>; the SPD at that position needs an Iscpv rating at or above roughly 68 A. The SPD’s Iscpv must be equal to or greater than that figure at every location where it is installed.<\/p>\n\n\n\n

          The integrated thermal disconnector<\/h3>\n\n\n\n

          Because a DC arc has no natural current-zero, IEC 61643-31 requires the SPD to isolate itself on failure. In practice this is a thermal disconnector<\/strong> bonded to the varistor that opens the protection path when the element overheats at end of life. It is a mandatory safety element of a PV DC SPD, not a premium feature \u2014 a device without one has no place on the DC side.<\/p>\n\n\n\n

          When an external backup device is needed<\/h3>\n\n\n\n

          An external backup fuse or DC-rated disconnector is required only when the array’s prospective short-circuit current exceeds<\/em> the SPD’s Iscpv rating. Many PV DC SPDs are rated to withstand the full string short-circuit current and need no external backup at all; adding an unnecessary fuse only introduces an extra failure point and lead length. Read the SPD datasheet: it states the maximum array short-circuit current the device tolerates unaided and, where a backup is needed, the recommended rating. On larger plants, also specify a device with a remote signaling contact<\/strong> so an operator sees an end-of-life SPD on the monitoring system instead of opening cabinets to eyeball status flags.<\/p>\n\n\n\n

          \n

          Wiring configuration: standard 2-pole versus Y for grounded and floating arrays<\/h2>\n<\/blockquote>\n\n\n\n

          PV DC SPDs come in more than one internal topology, and the choice depends on the array’s earthing arrangement. The two you will meet are:<\/p>\n\n\n\n

            \n
          • Standard 2-pole:<\/strong> a varistor from the positive pole to earth and another from the negative pole to earth. Simple and appropriate for functionally earthed systems where that arrangement suits the array.<\/li>\n\n\n\n
          • Y-configuration (also called 3+0 or total protection):<\/strong> the positive and negative poles each connect through a varistor to a common node, and that node connects to earth through a gas discharge tube (spark gap). Because the spark gap blocks continuous DC to earth, a single failed varistor cannot create a permanent pole-to-earth fault, and the arrangement suits both floating (unearthed) and functionally earthed arrays. It is the configuration most PV DC SPDs use for exactly this reason.<\/li>\n<\/ul>\n\n\n\n

            Match the configuration to the array’s earthing arrangement and confirm it against the SPD datasheet; a device chosen only on voltage and current but wired in the wrong topology can leave a mode of protection ineffective or introduce leakage.<\/p>\n\n\n\n

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            Earthing, bonding, and conductor sizing<\/h2>\n<\/blockquote>\n\n\n\n

            An SPD is only as good as the earth path it discharges into. The surge current the device diverts has to reach the mass of earth through a low-impedance route, and if that route is long, thin, or loosely terminated, the let-through voltage rises no matter how good the device’s Up is.<\/p>\n\n\n\n

              \n
            • Conductor cross-section.<\/strong> Size the SPD’s connecting and earthing conductors for the surge, not just the working current. Common installation practice (IEC 60364-5-53) is at least 6 mm\u00b2 copper for a Type 2 device and at least 16 mm\u00b2 copper for a Type 1 or Type 1+2 device that carries partial lightning current. Confirm the figure against local wiring rules and the SPD instructions.<\/li>\n\n\n\n
            • Equipotential bonding.<\/strong> Bond the SPD’s earth terminal to the array frame earthing and the main earthing system so that, during a surge, the whole installation rises and falls together and no dangerous potential difference appears across the inverter. On systems with a lightning protection system, this bonding is part of the LPS earthing design, not a separate afterthought.<\/li>\n\n\n\n
            • Terminations.<\/strong> Keep terminations tight and corrosion-protected in an outdoor combiner box; a high-resistance joint in the earth path quietly defeats the device.<\/li>\n<\/ul>\n\n\n\n

              Earthing is the part of the specification a datasheet cannot fix for you. Two identical SPDs, one with a short 16\u00a0mm\u00b2 bonded earth and one with a long undersized tail, protect the inverter very differently.<\/p>\n\n\n\n

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              Where to install, and the two rules that set let-through voltage<\/h2>\n<\/blockquote>\n\n\n\n
              \"\"<\/figure>\n\n\n\n

              An SPD only protects what sits close to it, so location is part of the specification, not an afterthought.<\/p>\n\n\n\n

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              • At the inverter DC input<\/strong> \u2014 unless the inverter already contains a coordinated DC SPD. This is the equipment you are protecting.<\/li>\n\n\n\n
              • At the array or combiner box<\/strong> \u2014 when the DC cable run between array and inverter exceeds roughly 10 metres. Beyond that distance a surge induced on the long DC cable can build enough voltage that one SPD at the far end no longer protects both ends, so protect at both.<\/li>\n\n\n\n
              • At the combiner and recombiner boxes<\/strong> \u2014 on multi-string and large ground-mount systems, one SPD per string group plus the DC disconnect, following the array’s protection zones.<\/li>\n<\/ul>\n\n\n\n

                Two installation rules then decide how much voltage actually reaches the equipment:<\/p>\n\n\n\n

                  \n
                1. The 0.5 m rule.<\/strong> Keep the total connecting-lead length \u2014 the loop through the live poles and the earth conductor \u2014 to about 0.5 m. Every extra length of lead adds inductive voltage (V = L \u00d7 di\/dt) on top of the device’s Up during a fast surge, so neat cabling routed the long way round the enclosure quietly raises the let-through voltage. Take the shortest path to the busbar and the earth bar.<\/li>\n\n\n\n
                2. Connect earth first.<\/strong> Establish the protective-earth path before the live conductors so the discharge path exists from the moment the SPD is live.<\/li>\n<\/ol>\n\n\n\n
                  \n

                  Read the datasheet: a PV DC SPD parameter decoder<\/h2>\n<\/blockquote>\n\n\n\n

                  A specification is only safe once you can read the datasheet without guessing. These are the lines that matter on a PV DC SPD, and what each one is telling you.<\/p>\n\n\n\n

                  Datasheet line<\/th>What it means<\/th>What to check<\/th><\/tr><\/thead>
                  Ucpv (Uc DC)<\/td>Maximum continuous DC operating voltage<\/td>\u2265 1.2 \u00d7 array maximum Voc, per mode of protection<\/td><\/tr>
                  Type \/ Class<\/td>Type 2 (Class II) or Type 1+2 (Class I+II)<\/td>Matches the lightning-exposure decision<\/td><\/tr>
                  Iimp (10\/350\u00a0\u00b5s)<\/td>Partial-lightning impulse current, Type 1 test<\/td>Present and adequate only where Type 1+2 is required<\/td><\/tr>
                  In (8\/20\u00a0\u00b5s)<\/td>Nominal discharge current, repeated duty<\/td>Sized to site exposure; the working rating<\/td><\/tr>
                  Imax (8\/20\u00a0\u00b5s)<\/td>Maximum single discharge current<\/td>Comfortable margin above expected surge<\/td><\/tr>
                  Up<\/td>Voltage protection level (let-through)<\/td>\u2265 20\u00a0% below the inverter DC withstand voltage<\/td><\/tr>
                  Iscpv \/ SCCR<\/td>Short-circuit withstand at the terminals<\/td>\u2265 array maximum short-circuit current at that point<\/td><\/tr>
                  Response time (tA)<\/td>How fast the element clamps<\/td>Nanosecond-order for MOV-based devices<\/td><\/tr>
                  Thermal disconnector \/ indicator<\/td>Internal fail-safe and status window<\/td>Present; green\/red or flag indication; pluggable module preferred<\/td><\/tr>
                  Remote signaling contact<\/td>Volt-free contact for monitoring<\/td>Specify on large or unattended plants<\/td><\/tr>
                  Operating temperature \/ IP<\/td>Environmental range and ingress rating<\/td>Suits the combiner-box climate and enclosure<\/td><\/tr>
                  Poles \/ mounting \/ terminals<\/td>2-pole or Y, 35\u00a0mm DIN rail, conductor capacity<\/td>Matches earthing arrangement and cable size<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n

                  If any of these lines is missing from a datasheet \u2014 particularly Ucpv, Iscpv, or the thermal disconnector \u2014 treat the omission as a reason to ask, not an assumption to make. A device that will not state its short-circuit withstand or its DC voltage rating is not documented for the DC side.<\/p>\n\n\n\n

                  \n

                  Don’t forget the AC side: protecting the whole PV system<\/h2>\n<\/blockquote>\n\n\n\n

                  A PV surge-protection specification that stops at the DC side is only half a specification. The same lightning or switching event that threatens the array reaches the inverter’s AC output and the point of connection to the building or grid, and that side needs its own SPD to IEC 61643-11 \u2014 an AC<\/em> device, sized to the AC system voltage (for example Uc around 275\u00a0V line-to-earth on a 230\/400\u00a0V system), not a DC device.<\/p>\n\n\n\n

                  Coordinate the two sides: a Type 2 AC SPD at the inverter output and main AC board for a building with no external LPS, or a Type 1+2 AC SPD at the origin where an LPS is present, mirroring the logic used on the DC side. JUTRION’s AC range \u2014 the JUSPD-40AC (Type 2) and JUSPD-12.5AC (Type 1+2) \u2014 covers this side to the same standards, so a single supplier can provide a coordinated DC-and-AC set rather than two unmatched halves.<\/p>\n\n\n\n

                  \n

                  Monitoring, maintenance, and replacement<\/h2>\n<\/blockquote>\n\n\n\n
                  \"\"<\/figure>\n\n\n\n

                  An SPD is a wear part. Every surge it diverts consumes a little of the varistor’s life, and the device is designed to reach end of life and disconnect rather than fail catastrophically. Specifying for that lifecycle is part of selection, not a separate maintenance topic.<\/p>\n\n\n\n