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 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.
| 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|
Fig. J31: Table of Iimp values according to the building's voltage protection level (based on IEC/EN 62305-2)
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.