Series K surge protective devices protect low-voltage switchboards against surges from the supply network and against the effects of lightning current entering the building's lightning-protection system. The K1 version is Type 1+2 according to IEC 61643-11, withstands a 10/350 µs impulse and is suitable at the incoming supply of a lightning-protected facility. The K2 version is Type 2 - installed downstream of a Type 1 SPD or where the only risk comes from induced and switching surges.
The family is modular. Sets with a neutral-to-earth path, identified by the letter G in the type code, are intended for TT and TN-S systems; a three-module set is sufficient for TN-C systems, while a single N–PE module can complement a switchboard already equipped with phase protection. Phase paths carry 20 kA with an 8/20 µs waveform, and the K1 version additionally carries 12.5 kA with a 10/350 µs waveform. The N–PE path is considerably stronger because in a TT system it carries equalization current between neutral and the earthing busbar. The voltage protection level increases with operating voltage - from about one kilovolt for the 175 V version to two kilovolts for the 440 V version - and this value is compared with the impulse withstand of the protected equipment.
Short-circuit withstand of 25 kA and an allowable upstream fuse up to 315 A gG mean that a typical switchboard does not require a separate SPD backup fuse. The plug-in design separates the current path from the mechanism retaining the cartridge: wiring remains in the base while the cartridge can be removed by hand - for insulation-resistance testing or replacement after years of service. Cartridge condition is shown by an indicator, and versions with a microswitch, identified by the -M suffix, provide this signal to the monitoring system.
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