A surge protective device limits the voltage that reaches the driver. IEC 61643-01:2024 and IEC 61643-11:2025 define three SPD Types, T1, T2 and T3, sitting at the service entrance, the board and the load. The 2011 edition called the same three “classes of test”, which is why datasheets still say both. Which of them a site needs is a risk question the wiring rules already answer.
Four ideas to carry into the next specification conversation you have.
A direct strike is rare. Indirect (induced) surges from distant strikes and switching of motors, transformers, capacitor banks are constant. SPDs protect against both.
T1 is tested with impulses simulating partial lightning current at the entrance, T2 with the 8/20 µs impulse at the board, T3 with a combination wave at the load. Coordinated together they reduce the risk; nothing makes it zero.
What decides survival is the voltage protection level Up, plus whatever the connecting leads add, against the equipment's rated impulse withstand Uw. kA figures from different test classes are not the same quantity.
A small surge does not always trip the breaker. It can degrade the driver's input stage, which fails later for no visible reason. Surge events leave no trace, until the warranty claim.
Test classes per IEC 61643-11; the type 1/2/3 names come from the installation standards. Whether a site needs them, and how many stages, is decided by IEC 60364-4-44 clause 443 and SBC 401 chapter 44.
| Type | Where it goes · waveform | Published quantity |
|---|---|---|
| Type 1 (Class I) | Service entrance · 10/350 µs | Iimp 12-25 kA |
| Type 2 (Class II) | Sub-distribution · 8/20 µs | Imax 40-60 kA · In 20 kA |
| Type 3 (Class III) | At the load (fixture) · combination | Uoc 6 kV (combination wave) |
| Type 1+2 combo | Single device covers entrance + panel | Iimp 12.5 kA · Imax 40 kA |
| Type 2+3 combo | Sub-panel + load in one box | Imax 40 kA · Up < 1.5 kV |
| Streetlight in-line SPD | Inside the pole/fixture body | 10 kA · Up < 1.2 kV |
| DC-side SPD (solar streetlight) | PV input on hybrid systems | 10 kA DC |
Five practical points that turn a spec line into a working installation.
Stages in series only work if each one discharges no more energy than the next can survive. The upstream device clamps at a HIGHER voltage, not a lower one, so what matters is the let-through energy reaching the downstream stage, and the decoupling (impedance or a stated cable length) between them. Manufacturers publish coordination tables; ask for the coordination statement for the stages together.
Every metre of connecting conductor adds roughly 1 µH of inductance. On an 8/20 µs wave at 8 kA the current rises at about 1 kA/µs, so each metre adds roughly 1 000 V on top of Up. SPD-to-load cable should be < 0.5 m where possible, and the protective earth path equally short.
Most SPDs use Metal-Oxide Varistors. Every clamping event slightly degrades the MOV. A status indicator (green = OK, red = failed, sometimes a remote signalling contact) is how a site finds out. Specify the indication and a written inspection route with the device, not just the device.
If the building has a lightning protection system (LPS) per IEC 62305, the LPS must terminate into a Type 1 SPD at the service entrance, designed for the full 10/350 µs lightning waveshape. Type 2 alone will not survive a direct strike's energy.
Pole-mounted roadway and outdoor high-bay luminaires sit in the most exposed category there is, so specify an in-line SPD between the incoming line and the driver and check the fixture's own published surge row against it. This is the third stage of coordination, and it is the stage that decides whether a storm costs a plug-in module or a luminaire.
We supply and install IEC 61643-coordinated SPD systems, T1 at the service entry, T2 at distribution, and a T3 stage at the luminaire where the project calls for it. Check each fixture’s own published surge row: most catalogue rows state an immunity level, not a device rating.
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