Electro-magnetic discharge (lightning) damage is not covered under warranty. The recommendations in this guide, when followed correctly, give the user the best protection from the harmful effects of EMD. However 100% protection is neither implied nor possible.
To protect structures, equipment and people against power surges (typically caused by lightning) by conducting the surge current to ground via a separate preferential solid path. The actual degree of protection required depends on local conditions and applicable local regulations. Cambium recommends cnPilot installation is contracted to a professional installer.
Refer international standards IEC 62305-1 and IEC 62304-4, the U.S. National Electric Code ANSI/NFPA No. 70-2017 or section 54 of the Canadian Electric Code for details of lightning protection methods and requirements.
Lightning Protection Installation Zones
The “rolling sphere method” (Figure 1) is used to determine the safe zone to install the Lightning Protection 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) as shown in the below figure. Similarly, where the sphere rests on two finials, the space under the sphere is considered as in the zone of protection.
Figure 1: Rolling sphere method to determine the lightning protection zones
Assess locations on poles, towers and buildings to determine, whether 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 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.
Implement the following requirements, When routing, fastening and connecting grounding cables:
- Make sure the grounding conductors run as short, straight, and smoothly as possible, with the minimum bends and curves.
- Do not install the grounding cables with drip loops.
- All bends must have a minimum radius of 203 mm and a minimum angle of 90° as shown in the below figure. A diagonal run is preferable to a bend, even though it does not follow the contour or run parallel to the supporting structure.
- Route all bends, curves and connections towards the grounding electrode system, ground rod, or ground bar.
- Securely fasten the grounding conductors.
- Use the braided grounding conductors.
- Use the approved bonding techniques for the connection of dissimilar metals.
Figure 2: Grounding cable minimum bend radius and angle
General Protection Requirements
To adequately protect AP installation for both ground bonding and transient voltage, surge suppression is required.
Implement the following basic protection requirements:
- Install the equipment in ‘Zone B’
- Ground the AP to the supporting structure.
- If additional surge protection is required, then install one more Surge Suppressor near the AP.
- Install the 56V-Gigabit Surge Suppressor (1000SS) within 600 mm of the point at which the power cable enters the building or equipment room.
- Ground the drop cable at the building entry point.
- Make sure the drop cable is not laid alongside a lightning air terminal.
- All grounding cables must be a minimum size of 10 mm2 csa (8AWG), preferably 16 mm2 csa (6AWG), or 25 mm2 csa (4AWG).
Pole or Tower Mount Guidelines
If you need to install AP to a metal tower or pole, then in addition to the general protection requirements, follow the below requirements also:
- Make sure the position of the equipment is lower than the top of the tower or its lightning air terminal.
- Make sure the metal tower or pole is correctly grounded.
- Install a grounding kit at the first point of contact (top), between the drop cable and the tower.
- Install a grounding kit at the bottom of the tower, near the vertical to horizontal transition point.
If grounding kit is installed, make sure the grounding kit is bonded to the tower or tower ground bus bar (TGB).
Connection examples of pole or tower installations are shown in the below figure.
Figure 3: Grounding and lightning protection on pole or tower
Wall Mount Guidelines
If you need to install AP on the wall of a building, then in addition to the general protection requirements, follow the below requirements also:
- Make sure the position of the equipment is lower than the top of the building or its lightning air terminal.
- Make sure the building is correctly grounded.
Connection examples of wall installations are shown in the below figure.
Figure 4: Grounding and lightning protection on wall
1. If Aux Port is used to power a secondary device, the maximum cable length between Access Point and the secondary device is 5 meters.
2. Secondary Device is allowed to install 0.6 meters below the highest point on the metal mounting pole as shown in the figure 3.
3. If Aux port is used for only LAN connection between AP and secondary device. If cable length exceeds 5 meters or if the secondary device is installed on a different pole, then additional Gigabit Surge Suppressor is recommended between AP and Secondary Device.
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