PMP 450 Planning Guide
Lightning protection zones
The ‘rolling sphere method’ (
) is used 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 22 Rolling sphere method to determine the lightning protection zones
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Assess locations on masts, towers and buildings to determine if the location is in Zone A or Zone B:
•
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.
Never mount equipment in Zone A. Mounting in Zone A may put equipment, structures and life at risk.
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Summary of Contents for PMP 450
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