To protect an electrical installation in a building, simple rules apply for the choice of

1. SPD(s);

2. its protection system.

For a power distribution system, the main characteristics used to define the lightning protection system and select a SPD to protect an electrical installation in a building are:

1. SPD

1.1 quantity of SPD

1.2 type

1.3level of exposure to define the SPD’s maximum discharge current Imax.

2. Short circuit protection device

2.1 maximum discharge current Imax;

2.2 short-circuit current Isc at the point of installation.

The logic diagram in the Figure 1 below illustrates this design rule.

Fig.1 – Logic diagram for selection of a protection system

The other characteristics for selection of a SPD are predefined for an electrical installation.

1. number of poles in SPD;

2. voltage protection level Up;

3. operating voltage Uc.

This sub-section Design of the electrical installation protection system describes in greater detail the criteria for selection of the protection system according to the characteristics of the installation, the equipment to be protected and the environment.