What is the rolling sphere method?

It's a geometric method to determine the placement of air terminals. A sphere of a radius defined by the LPL (e.g., 20m for LPL I) is 'rolled' over the structure; any part of the structure the sphere cannot touch is considered a protected zone.

What is the minimum cross-section for a copper down-conductor strip?

50 mm², with a minimum thickness of 2 mm (Table 6).

How often should a lightning protection system be tested?

Complete inspection and testing should be done at intervals not exceeding 2-4 years for standard structures, and more frequently (e.g., 1-2 years) for critical systems or in highly corrosive environments (Clause E.7).

What is the difference between IS/IEC 62305 Part 3 and Part 4?

Part 3 deals with protecting the structure itself from physical damage and protecting people from injury. Part 4 deals with protecting the internal electrical and electronic systems from the effects of lightning electromagnetic impulse (LEMP).

IS/IEC 62305 Part 3

: 2010

Protection against lightning - Part 3: Physical damage to structures and life hazard

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This standard provides requirements for the protection of structures against physical damage by means of a lightning protection system (LPS), and for protection of life against injury from touch and step voltages. It details the design, installation, and maintenance of external LPS components like air-termination systems, down-conductors, and earth-termination systems based on a risk-assessed Lightning Protection Level (LPL).

Specifies requirements for protection measures against physical damage to structures and danger to life within the structure caused by lightning flashes.

Quick Reference Values

Rolling sphere radius for LPL I20 m

Rolling sphere radius for LPL IV60 m

Minimum cross-section for copper down-conductor tape50 mm²

Minimum thickness of steel sheet as natural air-terminator4 mm

Maximum mesh size for air-termination (LPL I)5 m x 5 m

Recommended earth resistance for LPS< 10 Ohms

Key Formulas

s = ki * (kc / km) * l — Separation distance to prevent dangerous sparking

Practical Notes

The selection of the Lightning Protection Level (LPL) is not arbitrary; it must be determined using the detailed risk assessment methodology in IS/IEC 62305-2.

Proper earthing is the most critical and often weakest link in an LPS. Achieving and maintaining low earth resistance (<10Ω) is paramount for effective dissipation of lightning current.

Pay close attention to the separation distance 's' calculation to prevent side-flashing to internal metallic services, which can cause fires and damage sensitive equipment.