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Grounding and Lightning Protection in Vaisala Outdoor Installations Technical Reference

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User guide

When designing a lightning protection system and the grounding of a site, take into account the structure to be protected and the needed protection level, as well as technical, geographic, and economic factors.

Before you start constructing a lightning protection system, design the system and make preparations at the intended site or location.

To design a cost-efficient lightning protection system:

  • Evaluate the probability and frequency of strikes during the intended service lifetime of the system.
  • Consider the location and whether protection is needed for equipment only or for equipment and people.
  • Take into account environmental factors, such as wind load, possible floods, heavy rain, earthquakes, and corrosive atmosphere, and the mechanical and chemical properties of the soil.

The presented field practices are intended to protect only the installed equipment with a low probability of failure. If the system installation resides in an area of high lightning density (more than 5 lightning strikes per 1 km2/0.39 mile2 per year) or a contract requires compliance to a certain standard , follow the material dimensions in the referenced standards. See Reference Material.

Remember that no system, whether standard or non-standard, can guarantee 100 % protection.

Most Vaisala systems and instruments are designed to be grounded to ensure specified operation. Good examples are meteorological stations with sensors that are in connection with the ground, such as road surface sensors, and soil temperature and moisture sensors. Missing or faulty grounding can make the system unstable, causing it to produce erroneous data.

CAUTION External structures such as steel wiring that hold traffic signs or lights and similar may act as air terminals to lightning strikes. When using a pole that has a metal structure, ensure that the pole and all the equipment and external structures that are connected to it are properly grounded. If grounding is not possible, a separate pole mast for the sensors is recommended.

Situations where a lightning protection system may not be feasible are:

  • The protected system is inexpensive and protection would cost more than replacing the system.
  • The system is in place for a limited period of time, and in particular during season of low lightning intensity.
  • The system or construction is not tall or is lower than its surroundings.
  • The intensity of lightning strikes in the area is low throughout the year.
Although a lightning protection system may not be feasible in these cases, electrical safety grounding may be needed.