In short. Lightning protection has two parts: an external system that intercepts strikes and carries current to earth, and an internal system of bonding and surge protective devices (SPDs) that limits overvoltages on power and signal lines. Both need a common earthing system and coordinated stages.
External protection
- Air terminals (rods, mesh) intercept the strike.
- Down conductors carry the current.
- Earth termination spreads it into the ground. See electrode engineering.
The need and class of protection come from a risk assessment that considers structure, location, contents and consequences.
Internal protection and zones
The installation is divided into lightning protection zones, with SPDs at each boundary and bonding of all services.
| SPD location | Typical role |
|---|---|
| Service entrance / main board | Handles larger surge currents from outside |
| Sub-distribution | Reduces residual overvoltage |
| At sensitive equipment | Final limiting for electronics |
SPDs have ratings for maximum continuous voltage, discharge current and voltage protection level. They must be selected for the system earthing type and coordinated so that the upstream device handles energy and the downstream limits the residual voltage.
Installation rules
- Keep SPD leads short and direct, because lead inductance adds to the let-through voltage.
- Provide backup protection (fuse or breaker) as the manufacturer specifies.
- Bond to the main earthing terminal.
- Use status indication and replace after heavy surges.
Generators and controls
- Protect generator control panels, battery chargers and communication lines with SPDs.
- Run signal cables away from down conductors and use shielded cable with proper grounding.
- Bond the fuel tank, canopy and exhaust.
- Protect remote monitoring links, which are often the first to be damaged. See remote monitoring.
Inspection
Check air terminals, conductors and joints for corrosion and damage, test earth resistance, and check SPD indicators on a regular schedule and after storms.
Illustrative example
A generator station that lost its controller twice in storms receives a type 1+2 SPD at the main board, a type 2 at the generator panel and a type 3 for the controller supply, all with short leads and common bonding. Communication lines get data-line SPDs. Surge damage stops, and inspection shows the first-stage SPD has operated, so it is replaced.
The lightning protection chain
| Stage | Purpose |
|---|---|
| Air terminals and down conductors | Capture a strike and route it safely |
| Earth termination | Disperse the current into the ground |
| Equipotential bonding | Limit voltage differences within the building |
| Surge protective devices (SPDs) | Divert surge current on power and signal lines |
SPD coordination
SPDs are staged: Type 1 at the main incomer to handle large surge currents, Type 2 at distribution boards, Type 3 near sensitive equipment. Each stage reduces the surge so the next one sees less.
SPD selection points
- Maximum continuous operating voltage above the system maximum, allowing for generator voltage tolerance.
- Voltage protection level low enough for the equipment’s withstand.
- Discharge current rating suited to exposure.
- Short-circuit rating and backup fuse in line with the installation.
- Short, straight connection leads, because lead inductance adds to the voltage seen by equipment.
Local context
Hyderabad has intense pre-monsoon and monsoon thunderstorms. Controllers, battery chargers and communication ports of generator sets are especially exposed. Protect the control cabling and the ATS panel as well as the main supply.
Inspection
SPDs wear. Check status indicators after storms and replace as needed. See surge protection and earthing and bonding.
Common mistakes
- Long, looped SPD leads.
- Single SPD at the entrance with no downstream stage.
- No protection on signal lines.
What to send us
Send the site layout and incident history. Send your application details. See also earthing and bonding.
Questions engineers ask
Does a lightning rod protect electronics?
Not by itself. SPDs and bonding are needed for internal protection.
What is SPD coordination?
Arranging stages so that each handles the appropriate share of surge energy.
How do I know an SPD has failed?
Most have status indicators or alarm contacts. Check regularly.
Do I need lightning protection?
That depends on a risk assessment and local rules.
This guide gives general principles. Design should follow applicable lightning-protection standards.