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Type of external line Connection at entrance C LD C LI
Unshielded overhead line Undefined 1 1
Unshielded buried line Undefined 1 1
Power line with multi-grounded neutral conductor None 1 0.2
Shields not bonded to the same equipotential
Shielded buried line (power or telecommunication line) 1 0.3
bonding bar as equipment
Shields not bonded to the same equipotential
Shielded overhead line (power or telecommunication line) 1 0.1
bonding bar as equipment
Shields bonded to the same equipotential
Shielded buried line (power or telecommunication line) 1 0
bonding bar as equipment
Shields bonded to the same equipotential
Shielded overhead line (power or telecommunication line) 1 0
bonding bar as equipment
Lightning protection cable or wiring in lightning Shields bonded to the same equipotential 0 0
protection cable ducts, metallic conduit or metallic tubes bonding bar as equipment
No connection to external lines
(No external line) 0 0
(stand-alone systems)
Isolating interfaces
Any type 0 0
acc. to IEC 62305-4 (EN 62305-4)
Table 3.2.4.4 Values of factors C LD and C LI depending on shielding, earthing and insulation conditions

installations (SPM). A grid-like lightning protection system, cal fibre cables or optocouplers is used, it can be assumed that
shielding measures, installation principles for the cables, an P MS = 0.
increased rated impulse withstand voltage, isolating interfaces
and coordinated SPD systems are suitable protection measures The factors K S1 and K S2 for LPS or grid-like spatial shields can
to reduce P M . The probability P M is calculated as follows: be assessed as follows:

P = P P
M SPD MS K = 0.12 w
S1 m1
P SPD can be selected from Table 3.2.4.3 provided that a K = 0.12 w
coordinated SPD system which meets the requirements of S 2 m2
IEC 62305-4 (EN 62305-4) is installed. The values of the factor where w m1 (m) and w m2 (m) are the mesh sizes of the grid-
P MS are determined as follows:
like spatial shields or the mesh sizes of the meshed down con-
P = (K K K K ) 2 ductors of the LPS or the distance between the metal rods of
MS S1 S 2 S 3 S 4 the structure or the distance between the reinforced concrete
where structure acting as a natural LPS.
K S1 is the shielding effectiveness of the structure, LPS or
other shields at the boundaries LPZ 0/1;
The factor K S4 is calculated as follows:
K S2 is the shielding effectiveness of internal shields of the
structure at the boundaries LPZ X/Y (X > 0, Y > 1); K = 1
K S3 stands for the properties of the internal cabling (Table S 4 U
3.2.4.5); W
K S4 is the rated impulse withstand voltage of the system where U W is the rated impulse withstand voltage of the sys-
to be protected. tem to be protected in kV. The maximum value of K S4 is 1. If
equipment with different impulse withstand voltage values is
If equipment with isolating interfaces consisting of insulation installed in an internal system, the factor K S4 must be selected
transformers with an earth shield between the windings, opti- according to the lowest value of the impulse withstand voltage.

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