User guide

Grounding and lightning protection Chapter 2: Planning considerations
2-8
phn-2513_004v000 (Oct 2012)
Lightning protection zones
Use the ‘rolling sphere method’ (Figure 42) 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), consider the space under the sphere to be in the zone of protection (Zone
B). Where the sphere rests on two finials, consider the space under the sphere to be in the
zone of protection.
Figure 42 Rolling sphere method to determine the lightning protection zones
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.