Classification of Lightning Protection Systems

Posted on by Engr. Hamid Ali

In this post we are providing you an overview of Classification of Lightning Protection Systems (LPS). Lightning Protection Systems (LPS) are categorized into four classes (I, II, III, and IV). This classification is based on the level of lightning protection required. These classes are defined in IEC 62305 (Protection Against Lightning). The higher the class number, the lower the protection level — meaning Class I offers the highest protection and Class IV the lowest.

Introduction to Lightning Protection Systems (LPS)

Lightning is one of nature’s most powerful and unpredictable phenomena. A single lightning strike can release millions of volts of electricity, causing fires, equipment damage, power outages, or even loss of life. To safeguard structures and electrical systems from such destructive effects, we design and install different Lightning Protection Systems (LPS).

An LPS provides a controlled path for lightning current to travel safely from the point of strike to the ground, without passing through or damaging the structure. The goal is to intercept, conduct, and dissipate lightning energy in a safe and controlled manner.

Components of Lightning Protection System

A complete Lightning Protection System typically consists of following

  1. Air Termination System (ATS): Captures the lightning strike (e.g., air rods, meshed conductors).
  2. Down Conductor System: Provides a direct, low-resistance path to the ground.
  3. Earth Termination System: Safely disperses lightning current into the earth.
  4. Equipotential Bonding & Surge Protection Devices (SPDs): Protect electrical and communication systems from transient overvoltages.

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Classes of Lightning Protection Systems (LPS)

According to IEC 62305, Lightning Protection Systems are divided into four classes (I, II, III, and IV), depending on the level of protection required and the potential risk to the structure or facility.

Following are four classes of LPS

Highest Level of Protection– Class I LPS

  • Purpose: Used for very critical or sensitive structures (e.g., power plants, substations, explosive facilities, data centers).
  • Lightning current parameters: Designed to handle the strongest lightning currents.
    • Peak current: 200 kA (10/350 µs)
  • Protection radius: Smallest (more air terminals and down conductors needed).
  • Typical applications:
    • 380kV/132kV substations
    • Petrochemical plants
    • Military installations
    • Communication towers

High Level of Protection– Class II LPS

  • Purpose: For important industrial or commercial buildings where damage or downtime is significant but not catastrophic.
  • Lightning current parameters:
    • Peak current: 150 kA (10/350 µs)
  • Protection radius: Slightly larger than Class I.
  • Typical applications:
    • 132/13.8kV substations
    • Large factories
    • Hospitals and schools

Moderate Level of Protection–Class III LPS

  • Purpose: For ordinary structures with moderate risk of lightning strikes.
  • Lightning current parameters:
    • Peak current: 100 kA (10/350 µs)
  • Protection radius: Larger — fewer air terminals and down conductors.
  • Typical applications:
    • Commercial buildings
    • Residential complexes
    • Warehouses

Basic or Minimum Protection– Class IV LPS

  • Purpose: For low-risk structures or where lightning protection is optional.
  • Lightning current parameters:
    • Peak current: 100 kA (10/350 µs) but with less stringent spacing.
  • Protection radius: Largest — minimal coverage.
  • Typical applications:
    • Small residential buildings
    • Farm buildings
    • Rural shelters

Comparison Table: LPS Classes I to IV

This table provides a side-by-side comparison of the key technical parameters that define each class. These parameters dictate the physical design of the LPS.

Feature / ParameterClass I (Highest Protection)Class IIClass IIIClass IV (Lowest Protection)
Lightning Protection Level (LPL)IIIIIIIV
Probability of Interception99%97%91%84%
Maximum Current it can withstand (Imax)200 kA150 kA100 kA(Not specified, implied lower)
Minimum Peak Current for Interception3 kA5 kA10 kA15.7 kA
Rolling Sphere Radius (r)20 m30 m45 m60 m
Protection Angle (α)SmallestMediumLargerLargest
Mesh Size (for air-termination grid)5m x 5m10m x 10m15m x 15m20m x 20m