Selection of a Type 1 SPD
From Electrical Installation Guide
Impulse current Iimp
- Where there are no national regulations or specific regulations for the type of building to be protected:
- the impulse current Iimp shall be at least 12.5 kA (10/350 µs wave) per branch in accordance with IEC 60364-5-534.
- Where regulations exist:
- standard IEC 62305-2 defines 4 levels: I, II, III and IV
The table in Figure J31 shows the different levels of Iimp in the regulatory case.
Fig. J30 – Basic example of balanced Iimp current distribution in 3 phase system
Fig. J31 – Table of Iimp values according to the building's voltage protection level (based on IEC/EN 62305-2)
| Protection level as per EN 62305-2 | External lightning protection system designed to handle direct flash of: | Minimum required Iimp for Type 1 SPD for line-neutral network |
|---|---|---|
| I | 200 kA | 25 kA/pole |
| II | 150 kA | 18.75 kA/pole |
| III / IV | 100 kA | 12.5 kA/pole |
Autoextinguish follow current Ifi
This characteristic is applicable only for SPDs with spark gap technology. The autoextinguish follow current Ifi must always be greater than the prospective short-circuit current Isc at the point of installation.
