Chapter 3: System planning
Site planning
Page 3-9
Lightning protection zones
Use the rolling sphere method (
Figure 41
) to determine where it is safe to mount equipment. An
imaginary sphere, typically 50 meters in radius, is rolled over the structure. Where the sphere rests
against the ground and a strike termination device (such as a finial or ground bar), all the space
under the sphere is considered to be in the zone of protection (Zone B). Similarly, where the
sphere rests on two finials, the space under the sphere is considered to be in the zone of
protection.
Figure 41 Rolling sphere method to determine the lightning protection zones
Zone A: In this zone a direct lightning strike is possible. Do not mount equipment in this zone.
Zone B: In this zone, direct EMD (lightning) effects are still possible, but mounting in this zone
significantly reduces the possibility of a direct strike. Mount equipment in this zone.
Warning
Never mount equipment in Zone A. Mounting in Zone A may put equipment,
structures and life at risk.
