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.