Type 1 vs Type 2 PV SPDs: Which Does Your Solar Array Need?

• What this guide settles
• Type 1 and Type 2 are test classes, not quality tiers
• The PV DC side follows its own rulebook: IEC 61643-31 tests, IEC 61643-32 selects
• When the DC side needs a Type 1
• When a Type 2 is the right call
• They are layers, not alternatives
• A five-step selection sequence for specifiers
• Frequently asked questions
• Confirm the Applicable Class Before You Buy
• Request an Applicable-Grade Review
• Contact CRESIN for PV Surge Protection Solutions

Choosing the wrong surge protective device (SPD) class on the DC si de of a PV system is one of the most common — and most expensive — errors in solar design. Type 1 and Type 2 are not quality grades; they are test classes in IEC 61643-31, matched to different surge regimes: Type 1 for partial lightning current (10/350 µs), Type 2 for induced surges and switching transients (8/20 µs). This guide gives design institutes, EPCs and procurement teams the decision logic and the checks that keep a PV DC protection design defensible.

For PV design institutes, EPCs, procurement managers · Standards: IEC 61643-31 · IEC 61643-32 · Read time: 8 min

What this guide settles

1. The class is decided by the installation point, not by preference: an SPD that can carry partial lightning current must be Type 1 (or 1+2).
2. Only Iimp at 10/350 µs proves Type 1; In/Imax at 8/20 µs proves Type 2. Never read one figure as the other.
3. A Type 2 is the baseline for most PV DC circuits — arrays separated from the LPS, ground plants with meshed earthing. It cannot replace a Type 1 where one is required.

Type 1 and Type 2 are test classes, not quality tiers

An SPD's type is decided by the test waveform it must survive, not by its housing, brand or price. For the DC side of photovoltaic installations, IEC 61643-31 (requirements and test methods for SPDs connected to the DC side of PV systems) defines the classes:

• Type 1 (Class I) — tested with the 10/350 µs impulse, rated by Iimp. The waveform simulates partial lightning current — the fraction of a direct strike flowing through the installation — and its long tail carries high transferred charge and specific energy.
• Type 2 (Class II) — tested with the 8/20 µs wave, rated by In (nominal) and Imax (maximum discharge current). It covers induced surges from nearby strikes and switching transients from PV and grid equipment; it decays quickly and carries far less energy at the same peak.
• Type 1+2 (combined) — a single device carrying both an Iimp rating and In/Imax ratings.

At the same peak current, a 10/350 µs impulse delivers roughly ten to twenty times the energy of an 8/20 µs impulse. A Type 2 device at a partial-lightning-current point fails destructively on the first direct-strike event. And Iimp is never interchangeable with Imax: they are tested with different waveforms and answer different questions.

Table 1. Comparison of Type 1 and Type 2 PV DC SPDs

Figure 1. The test waveforms behind the classes: Type 1 must survive the long-tail 10/350 µs impulse; Type 2 is verified with the fast-decay 8/20 µs wave.

The PV DC side follows its own rulebook: IEC 61643-31 tests, IEC 61643-32 selects

Two IEC documents work together on the DC side, and confusing them causes real specification errors. IEC 61643-31 is the test standard: it sets requirements and test methods for SPDs connected to the DC side of PV systems, defines Uc, In, Imax, Up and TOV in a DC context, and classifies devices as Type 1, Type 2 or Type 1+2. Because a DC circuit has no natural current zero-crossing, a PV DC SPD must interrupt follow current under DC arc conditions — a device certified only to IEC 61643-11 (the AC standard) is not, by that certificate, confirmed suitable for the PV DC side.

IEC 61643-32 is the selection standard: it covers the selection, installation and coordination principles for SPDs on the DC side of PV installations up to 1,500 V DC, including rooftop systems and ground-mounted free-field plants with meshed earthing. Part 31 answers "does the product pass the tests?", Part 32 answers "where and how do I select it?" — A certificate that covers only the AC requirements does not demonstrate compliance for a DC-side SPD. This is a common compliance gap in PV projects. For more details, see our clause-by-clause guide to IEC 61643-31.

When the DC side needs a Type 1

On the PV DC side, Type 1 is triggered by one condition: the DC circuit can carry a share of the lightning current. Following IEC TR 63227 and the separation-distance logic of IEC 62305-3, a Type 1 (or 1+2) SPD is recommended when:

1. An external LPS (air terminals and down conductors) is installed on the structure, and
2. The required separation distance between the LPS and the array or DC cabling is not maintained.

Typical cases: a rooftop array bonded into an air-termination network; a DC combiner or inverter inside a building with an LPS; long DC runs routed close to down conductors. The SPD at the DC boundary then discharges partial lightning current (10/350 µs).

Verification rule: Type 1 is proven only by an Iimp rating tested at 10/350 µs. A datasheet quoting only In/Imax at 8/20 µs is not a Type 1 demonstration — ask for the Iimp test data before the device enters the bill of materials.

Figure 2. Decision tree for the PV DC side (per IEC TR 63227 / IEC 62305-3; classes per IEC 61643-31). A Type 2 never substitutes for a Type 1 at a partial-lightning-current point.

When a Type 2 is the right call

• No external LPS, or separation distance maintained. The array and its DC cabling sit in the induced-surge zone. Type 2 SPDs per IEC 61643-31 go at the array / combiner side and the inverter DC input; with a short cable run between them, one protected point can cover both.
• Ground-mounted and free-field plants with meshed earthing. Multiple earthing points distribute the strike current, so Type 2 SPDs at the inverter DC input are the norm.
• Type 2 remains the baseline even where Type 1 is present. A Type 1 alone cannot protect sensitive electronics, so a coordinated Type 2 is still required closer to the equipment.

The caveat cuts the other way: Type 2 handles the induced regime, not partial lightning current. Specifying it at a partial-lightning-current point is the misconfiguration that produces field failures after the first direct strike.

They are layers, not alternatives

Type 1 and Type 2 are layers in a coordinated cascade, not alternative products. A Type 1's Up is generally too high to protect inverter electronics by itself, so a coordinated Type 2 is still needed closer to the equipment; a Type 1 where only Type 2 is required adds cost without benefit.

The combination covering most commercial and utility PV projects: Type 2 DC SPDs per IEC 61643-31 at the array and inverter DC input, plus a Type 2 AC SPD per IEC 61643-11 at the inverter output, coordinated so the stages share surge energy in sequence. Where the AC circuit can carry partial lightning current, specify a Type 1 AC SPD per IEC 61643-11 — such as the CRESIN CSMS-A15 (Iimp 15 kA at 10/350 µs) — and never substitute a Type 2 for it.

Figure 3. A Type 2 PV DC SPD (CRESIN CSMS-B40) declared to IEC 61643-31. Its In/Imax ratings at 8/20 µs define the class; it carries no Iimp (10/350 µs) rating.

For more information about our complete range of DC and AC surge protection solutions and recommended SPD installation locations in PV systems, explore the CRESIN solar PV surge protection overview and the CSMS-B40 product page.

A five-step selection sequence for specifiers

1. Establish the lightning context. External LPS present? Separation distance to array and DC cabling maintained (IEC 62305-3)? This decides whether Type 1 is in scope.
2. Fix the class at each DC SPD point per IEC 61643-32: Type 1 / 1+2 at boundary points that can carry partial lightning current; Type 2 elsewhere.
3. Lock the DC parameters. Uc above worst-case cold-weather Voc — computed from the actual string configuration, not assumed; select the matching Uc grade from the device range (the CSMS-B40 offers DC 670/1200/1500/1800 V); In/Imax matched to exposure; Up below the inverter's impulse withstand; TOV confirmed.
4. Verify the certificate. Standard part IEC 61643-31 (not only 61643-11); certified model matches the delivered product; and Iimp at 10/350 µs for any Type 1 claim.
5. Coordinate both sides. DC per IEC 61643-31, AC per IEC 61643-11, respecting cascade distances so the two stages share surge energy in sequence.

Frequently asked questions

Can a Type 2 PV SPD replace a Type 1?

No. They use different test waveforms (8/20 vs 10/350 µs); a Type 2 device at a partial-lightning-current point can fail destructively on a direct strike.

Does a rooftop array without lightning rods need a Type 1?

Usually Type 2. Type 1 becomes necessary when the building has an external LPS and the separation distance to the array or DC cabling is not maintained.

What does "Type 1+2" mean on a PV DC SPD?

A device tested to both waveforms per IEC 61643-31: Iimp at 10/350 µs plus In/Imax at 8/20 µs — one unit covers a boundary point and downstream induced surges.

How do I verify a PV DC SPD is genuinely Type 1 or Type 2?

Check the certificate: Iimp at 10/350 µs proves Type 1; In/Imax at 8/20 µs proves Type 2. The standard part must be IEC 61643-31 and the certified model must match the offered product.

What Uc do I need for a 1500 V PV system?

Uc must exceed the array's worst-case cold-weather Voc — a value set by the string configuration (module type, temperature coefficient, series count), so no single Uc is a universal rule. The CSMS-B40 covers the DC 600–1500 V classes with Uc grades of 670/1200/1500/1800 V; select the grade that clears the computed Voc.

Do I need both a DC and an AC SPD?

In most utility and commercial projects, yes: a DC-side device per IEC 61643-31 and an AC-side device per IEC 61643-11, coordinated as a cascade.

Confirm the Applicable Class Before You Buy

The class decision depends on documents no datasheet can show: the building's external lightning protection design and the PV single-line layout. Submit your building LPS documentation and PV design drawings for an applicable-grade review. The CRESIN technical team will confirm the SPD class at each point, the DC/AC coordination, and the Uc, In/Imax, and Up values against your string configuration.

Request an Applicable-Grade Review

Where the review identifies a partial-lightning-current point, the specification must call for a Type 1 or Type 1+2 device per IEC 61643-31. The review will state this explicitly in the recommendations.

Contact CRESIN for PV Surge Protection Solutions

Need help selecting the right SPD for your photovoltaic project? Contact the CRESIN technical team for product information, technical support, and customized DC/AC surge protection solutions. We can help you evaluate your project requirements and identify suitable SPD configurations.

Contact Us

Website: https://www.cresinspd.com/

Email: [evagu@cresinspd.com]