Before going into common mistakes, let’s quickly go address ones that are less common but still bad:
- Installing an “active protection” system. In theory, these don’t work and we have proof they don’t work in practice either.
- Using unlisted parts. There are good reasons these aren’t listed for lightning protection.
- Using the standards as mere guidelines. The standards will give you a reliable system that does the intended job. Insurers are fond of that fact.
Some common mistakes:
- Using the incorrect model for laying out the system of air terminals. Several factors are involved in determining where the air terminals should go and how many you need. NFPA 780 devotes significant space (including several illustrations) to getting this right.
- Leaving metallic objects unbonded on the roof. A flashover occurs when lightning jumps from a metallic object at one potential to another metallic object that’s at a different potential. The arc can cause massive damage. By bonding all metallic objects on the roof, you eliminate the differences of potential that risk big flashovers.
- Making bends too sharp. It’s not that the system captures lightning, but that lightning takes a preferred path. Lightning can jump across sharp bends or from a sharp bend to a nearby object.
Letting downconductors develop U or V pockets. These create a jump risk. Keep the conductors on a horizontal or downward path.
Source: Mark Lamendola | Mindconnection