Lightning Protection System Design as per IEC 62305


Lightning strike is a natural phenomenon of sudden discharge of charges from highly concentrated cloud or any objects. Lightning cannot be avoided but the damages can be reduced by proper preventive measures. The complete protection includes properly designed and executed external and internal lightning protection system. In this article we have explained about Lightning Protection Design as per IEC 62305.

Lightning Protection System:

The designing of lightning protection system can be divided into 2 major parts as,

1. Risk assessment
2. Designing

Risk assessment:

Risk assessment is the measure of risk due to lightning strike and the probability of damages.

IS/IE 62305 - 2 explains about the damages due to lightning strikes, Source of such damages, losses due to lightning and the corresponding risks.

The damages due to lightning strike as specified by IS/IEC62305 part 2 are as follows.

  • Loss of human life / Injury (D1)
  • Physical damage (D2)
  • Electrical / Electronic components (D3)

Direct lightning strike on any given structure is not only source of damage. The risks are also caused by the
following sources.

  •  Direct lightning strikes on a structure (S1)
  • Lightning strikes adjacent to the structure (S2)
  •  Lightning strikes on the power lines connected to the structure (S3)
  • Lightning strikes adjacent to the line connected to the system (S4)

As per IS/IEC 62305, the losses due to the damages caused by lightning are categorized into four types as

  •  Loss of human life (L1)
  •  Loss of service to public(L2)
  •  Loss of cultural heritage (L3)
  •  Loss of economic (L4)

Different Types of Lightning Strikes

The risks due to each type of loss should be evaluated for designing the proper lightning protection system.

Picture Source: IS/IEC 62305-2

IS/IEC 62305 categorizes four types of risks corresponding to the four types of losses

  • Risk of loss of human life (R1)
  • Risk of loss of service to public(R2)
  • Risk of loss of cultural heritage (R3)
  • Risk of loss of economic (R4)

Each risk is the sum of the corresponding each risk components. Risk components to be considered for each
type of loss in a structure are listed below.

R1 = RA1 + RB1 + RC1 + RM1+ RU1 + RV1 + RW1 + RZ1
R2 = RB2 + RC2 + RM2 + RV2 + RW2 + RZ2
R3 = RB3 + RV3
R4 = RA4 + RB4 + RC4 + RM4 + RU4 + RV4 + RW4 + RZ4

Among these components RC1, RM1, RW1 and RZ1 are applicable for structures with risk of explosion and for hospitals. We have already explained about Risk and risk components in one of our previous articles and link for the same is provided on the description.

Flow Chart:

Lightning Protection Flow Chart

Design of lightning protection system:

IS/IEC 62305 -3 has given the procedure for designing a lightning protection for external system and IS/IEC 62305-4 has given the procedure for designing  lightning protection for internal system.

1. Lightning design shall be done with respect of class of lightning protection system.

2. The position of the air termination system shall be designed by using the following placement methods as specified by IS/IEC 62305-3

1) Protection Angle Method (
2) Rolling Sphere Method (
3) Mesh Method (

3. The distance between down conductors will depends on the class of lightning protection (

4. IS/IEC 62305  and IS 3043 has given the arrangement of earth termination system.

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