Before you commission a lightning protection project, it’s important to address some basics. Such as these:
- Determine the structure type. Chapter 4 of NFPA 780, one of the lightning protection standards, provides the requirements for “ordinary structures.” It doesn’t define this, except to say they are structures used for ordinary purposes. To decipher this, look at the titles for Chapters 5, 6, 7, and 8. If one of these does not describe your structure, it’s an ordinary structure.
- Determine the roof type (ordinary structure). This is all about the geometry of the air terminal pattern versus heights, angles, and distances involved in the roof shape. Based on the roof type, you’ll determine the layout of the air terminals.
- Locate the best paths for downconductors. The system is designed to preferentially take the lightning hit (through the air terminals) and conduct it via the rooftop conductor system down into the grounding system. Ideally, the downconductors will be equally spaced to provide the shortest paths for the lightning. But considerations such as locations of structural attachment points and nearby items come into play. For example, you don’t want to run a downconductor over a window or next to a fuel tank. A building corner is usually good, but ensure sure the route to there is unobstructed. And no sharp bends!
- Design the grounding electrode system. Know exactly where electrodes and conductors will go, before digging.
Source: Mark Lamendola | Mindconnection