After every major storm, service technicians see the same wave of failures: damaged routers, variable-frequency drives, boiler control systems, inverters, and cash registers. In most of these cases, lightning did not strike anywhere near the building. A surge was enough, a brief voltage spike that travelled through the electrical installation and reached the most sensitive equipment. This is precisely what a rooftop lightning protection system does not protect against.
An external lightning protection system has one purpose: to conduct a direct lightning strike safely into the ground and protect the building from fire and structural damage. It does not protect the electronic equipment inside the building. Surges can also result from lightning strikes to the power grid or ground hundreds of metres away, from electromagnetic induction in conductors, and from switching operations within the electrical network itself. Complete protection therefore consists of two layers: external lightning protection and internal surge protection, using surge protective devices installed in electrical distribution boards.
Surge protection is designed in stages, like a series of dams along a river. Type 1 surge protective devices, installed at the point where the power supply enters the building, discharge the highest-energy part of the surge. Type 2 devices, installed in distribution boards, reduce the remaining overvoltage to a level that the electrical installation can withstand. Type 3 devices, installed close to the most sensitive equipment such as servers, control systems, and medical devices remove the final residual voltage.
Each stage has a specific function, and no single stage can replace the others. A protected power strip on its own, without the preceding protection stages, may provide a feeling of security, but not actual protection. A surge protective device is a relatively simple component, but its installation determines how effectively it performs. The connecting conductors must be kept short because every additional metre of conductor increases the voltage that appears during a surge.
The building must also have proper equipotential bonding, because a surge will seek alternative paths through metal structures, pipes, cable shields, and other conductive parts. Signal lines, network cables, antenna connections, and telecommunications lines require their own surge protective devices as well. Electronic equipment is often damaged through precisely these routes from the direction no one thought to examine. Within the overall budget of a building, surge protection is a minor expense, often comparable to the cost of a single failed variable-frequency drive. Surge protective devices also have status indicators and should be checked during regular electrical inspections, because a device that has discharged a major surge may need to be replaced.
A modern facility filled with electronics, from the boiler room to the production line, is expensive equipment connected to the lottery of the weather forecast when it has no surge protection. With properly designed protection, every storm brings one less concern.
