Lightning protection systems (LPS) are critical for safeguarding buildings against lightning strikes. As per National Building Code of India and IS 2309, every structure must be evaluated for lightning risk and protected accordingly.

This guide covers:

• Lightning arrester design
• Risk assessment method
• IS & NBC guidelines
• ⚡ Risk calculator (included below)

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⚡ WHAT IS A LIGHTNING ARRESTER?

A lightning arrester is a device that:

• Intercepts lightning
• Safely conducts it to earth
• Prevents damage to structure & equipment

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📐 TYPES OF LIGHTNING PROTECTION SYSTEMS

🔹 Conventional System

• Franklin rod
• Down conductor
• Earthing

🔹 Early Streamer Emission (ESE)

• Advanced lightning rod
• Larger protection radius

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📊 DESIGN REQUIREMENTS (NBC + IS 2309)

🔥 Key Requirements:

• Protection for buildings > 15m height
• Proper earthing resistance (< 10 ohms)
• Minimum 2 down conductors
• Bonding of all metallic parts

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🧠 RISK ASSESSMENT (MOST IMPORTANT)

Lightning protection is based on:

• Building height
• Location
• Usage
• Lightning density

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⚡ BASIC RISK FORMULA

$R = N_g \times A_e \times C_d$R=Ng​×Ae​×Cd​

Where:

• $R$R = Risk
• $N_g$Ng​ = Lightning ground flash density
• $A_e$Ae​ = Effective collection area
• $C_d$Cd​ = Location factor

🔹 PART 1: RISK CALCULATION

Formula flow:

1. Collection Area

$$A_c = L×W + 2H(L+W) + 3.14×H^2$$

2. Probability

$$P = A_c × N_g × 10^{-6}$$

3. Weighting Factor

$$W_f = A × B × C × D × E$$

4. Overall Risk

$$R = P × W_f$$

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🧮 LIGHTNING RISK CALCULATOR (SIMPLE LOGIC)

📥 Inputs:

• Building length (m)
• Width (m)
• Height (m)
• Ng (lightning density)
• Location factor

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📊 Calculation Steps:

1. Effective Area:

$$A_e = L × W + 2 × H × (L + W) + \pi × H^2$$

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2. Risk:

$$R = Ng × Ae × Cd$$

⚙ DESIGN COMPONENTS

• Air terminals (rods)
• Down conductors
• Earth pits
• Surge protection devices (SPD)

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❌ COMMON MISTAKES

• Ignoring earthing resistance
• Wrong spacing of conductors
• No bonding
• Not calculating risk

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🏭 RECOMMENDED BRANDS

• OBO Bettermann
• Schneider Electric
• DEHN
• Furse

❓ FAQ

What is lightning density (Ng)?

Number of lightning strikes per km² per year.

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Is lightning protection mandatory?

Yes, for high-rise buildings as per NBC.

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What is safe earthing resistance?

Below 10 ohms (preferably <5 ohms).

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🎯 CONCLUSION

Lightning arrester design is not optional — it is a life safety requirement. Using proper IS code guidelines and risk assessment ensures optimal protection.

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