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Selection of a Type 1 SPD

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General rules of electrical installation design
Connection to the MV utility distribution network
Connection to the LV utility distribution network
MV and LV architecture selection guide for buildings
LV Distribution
Protection against electric shocks and electric fires
Sizing and protection of conductors
LV switchgear: functions and selection
Overvoltage protection
Energy Efficiency in electrical distribution
Power Factor Correction
Power harmonics management
Characteristics of particular sources and loads
PhotoVoltaic (PV) installation
Residential and other special locations
ElectroMagnetic Compatibility (EMC)


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. J30Basic example of balanced Iimp current distribution in 3 phase system

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. J31Table 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.