Surge protective devices (SPDs) are mandatory in most EU residential installations since 2016 (HD 60364-5-534). But which type goes where? And what about protecting KNX bus lines and DALI circuits? Here's the practical guide.

SPD type classification

Type 1 (T1): Class B, designed for direct lightning current (Iimp). Mandatory when the building has a lightning protection system (LPS/ESE). Installed in the main distribution board (MDB), as close as possible to the energy entry point. Test waveform: 10/350 μs. Typical Iimp: 25 kA per phase.

Type 2 (T2): Class C, designed for induced surge currents. Required in all new buildings in most EU countries. Installed in the main panel or sub-distribution board. Test waveform: 8/20 μs. Typical In: 20 kA, Imax: 40 kA.

Type 3 (T3): Class D, point-of-use protection. Installed at the equipment level (socket level). Not sufficient alone — must be used with T2 upstream. Typical Uc: ≤ 1.5 kV. Used for sensitive electronics (server, AV equipment).

SPD coordination

The critical rule: there must be at least 10m of cable between a T1 and T2 SPD. If less than 10m, use a coordination filter (decoupling inductor) or a T1+T2 combination device (Hager SPN440 or similar). Combination devices are increasingly popular for space-saving.

KNX bus line protection

The KNX TP bus runs at 29V DC and is typically separated from power cables. However, lightning-induced surges can couple into KNX data lines via inductive coupling. For KNX: install a KNX surge protector module at the IP router location (e.g. Hager TXA205B, MDT SPZ-0002.01) and at any location where KNX cable exits to a different building or outdoor equipment. These devices clamp to 50V and absorb the surge energy.

DALI and 0-10V line protection

DALI lines operating at 16V DC are similarly vulnerable. A DALI surge protection module (e.g. Phoenix Contact CLP 24DC) protects the DALI pair at the gateway output. For outdoor DALI (garden luminaires), this is mandatory.

Practical panel design

In a KNX residential panel: Row 1 = T2 SPD (3-phase or single-phase, as appropriate) immediately after the main switch. Row 2 = MCBs and RCDs. Row 3 = KNX devices (PSU, actuators, gateways). Add a KNX data line SPD inline on the TP bus. Add T3 at any point-of-use for KNX IP router and home servers.