Design rules of the electrical installation protection system

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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 & LV architecture selection guide
LV Distribution
Protection against electric shocks
Sizing and protection of conductors
LV switchgear: functions & selection
Protection against voltage surges in LV
Energy Efficiency in electrical distribution
Power factor correction and harmonic filtering
Power harmonics management
Characteristics of particular sources and loads
PhotoVoltaic (PV) installation
Residential electrical installations
ElectroMagnetic Compatibility (EMC)


To protect an electrical installation in a building, simple rules apply for the choice of
  • SPD(s);
  • 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:

  • SPD

  - quantity of SPD; 
  - type;
  - level of exposure to define the SPD's maximum discharge current Imax.

  • Short circuit protection device

  - maximum discharge current Imax;
  - short-circuit current Isc at the point of installation.

The logic diagram in the Figure J20 below illustrates this design rule.



Fig J20 EN.jpg

























Fig. J20: Logic diagram for selection of a protection system

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

  • number of poles in SPD; 
  • voltage protection level Up;
  • operating voltage Uc.

This sub-section J3 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.

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