In short. Lightning damage rarely comes from a direct strike alone. Surges travel along power, signal and earth conductors. A good scheme assesses the risk, gives lightning a safe path, bonds everything to one reference and protects each entry point with surge devices matched to its zone.
Layers of protection
- Risk assessment. Use a recognised method (for example IEC 62305) to decide the protection level from strike density, structure, services and consequence.
- External protection. Air terminals, down conductors and an earthing system to carry the strike safely.
- Equipotential bonding. Bond metal parts, cable trays, tanks and earth bars so potential differences stay low.
- Surge protective devices (SPDs). Install in stages at the incoming supply, distribution boards and sensitive equipment.
- Cable routing and shielding. Keep power and signal cables apart, shield and bond screens.
- Maintenance. Inspect and test regularly.
SPD staging
| Stage | Location | Role |
|---|---|---|
| Type 1 | Service entrance | Handles large lightning current |
| Type 2 | Distribution boards | Limits residual surges |
| Type 3 | At sensitive equipment | Fine protection |
Keep SPD leads short, since lead inductance adds to the let-through voltage. Coordinate stages by distance or by manufacturer guidance.
Generator and controller points
- Controllers, AVRs and battery chargers are sensitive. Protect their supply and signal lines.
- Remote monitoring, antennas and long sensor cables are common entry paths.
- Fuel tanks and outdoor sets need bonding and careful assessment of the zone.
- Transfer between utility and generator may change the earth reference. Keep the bonding consistent.
Illustrative example
A rooftop diesel set at a telecom site trips repeatedly after storms and its controller fails twice. The review finds that the control cabinet is fed from a long unprotected cable run and has no SPD, and the antenna cable shield is not bonded at the entry. Adding SPDs at the board and controller and bonding the shields stops the failures.
Risk-based approach
Lightning risk assessment under IEC 62305 weighs how often strikes occur against the consequences. It determines whether protection is needed and at what level.
Expected strikes per year Nd = Ng × Ad × Cd × 10⁻⁶, with Ng ground flash density per km² per year, Ad collection area in m² and Cd location factor
Illustrative calculation
With Ng = 4 per km² per year, a building collection area of 8,000 m² and Cd of 1: Nd = 4 × 8,000 × 1 × 10⁻⁶ = 0.032, or about one strike every 31 years. Compare with an acceptable frequency set by the risk assessment. Use local flash density data from an authoritative source.
Elements of the protection design
| Element | Role |
|---|---|
| External LPS: air terminals, down conductors, earthing | Capture and conduct strikes |
| Bonding | Prevent flashover between metalwork |
| SPD coordination | Protect power and signal lines |
| Shielding and cable routing | Reduce induced surges |
Generator-specific exposures
- Outdoor enclosures and exhaust stacks, which are tall metal structures.
- Long control and sensor cables.
- Battery chargers and controllers, which are sensitive electronics.
Local context
Hyderabad has strong thunderstorm activity in pre-monsoon and monsoon periods. Treat controllers and communication links as exposed.
See lightning and SPD coordination and surge protection.
Common mistakes
- Fitting an SPD with a long lead.
- Ignoring signal and communication lines.
- Separate earths for different systems.
What to send us
Send site layout and incident history. Send your application details. See also earthing architecture.
Questions engineers ask
Does an SPD make the site lightning-proof?
No. It limits surge voltage, within the device rating, as part of a system.
Do I need external lightning protection as well?
That depends on the risk assessment.
How often should SPDs be checked?
Follow the manufacturer indicators and inspect after storms and on schedule.
Why do controllers fail but not the engine?
Electronics tolerate far lower surge energy than mechanical parts.
This guide gives general principles. A lightning protection design must follow applicable standards.