Don't mess with Mother Nature

Dec 1, 2007 12:00 PM, By Matt Gauvin

Weatherproofing the EMP-protection devices is just as important as weatherproofing the feeder cable. All surge protectors that are mounted to the base of the tower, at the junctions, and at the jumper and feeder line exit and entry points should be weatherproofed.

Having selected the appropriate forms of protection to suit the base station's configuration, designers need to consider the connections to the site's grounding point. Every feeder run should have its own grounding. The grounding leads are connected to a bus bar at the base of the tower, which is connected in turn to a single ground rod, or a ground ring with multiple rods. The rods, which are generally 5 feet or more in length, are buried and disperse the energy into the ground.

A high-quality connection between the feeder's outer conductor and the grounding kit is a basic requirement. High-speed fitting allows the installer to be productive, but this needs to be achieved without loss of quality, otherwise cable lifetimes can be reduced, or work may need to be redone.

Tools are available that make the grounding job both easy and fast. For instance, stripping tools are designed specifically to remove the jacket material for grounding so installers aren't forced to use their knives to manually strip the cable off in the middle of the feeder run. This approach not only is quicker and cleaner, but it also takes the correct amount of material off without overstripping. Using these tools, installers don't have to worry about scratching, denting or damaging the cable.

For the connectors and the EMP-protection devices, applying the correct torque at the fitting stage is important. Good mechanical connection and electrical contact are required, but they must be achieved without overtightening. Using a torque wrench will achieve the desired result.

Although lightning strikes at BTS sites always will occur, the combination of careful design, appropriate protection devices, good tooling and expert installation will minimize the risks. Proper grounding and surge protection are small investments compared to the system replacement cost following a lightning strike. When lightning does hit a tower, everything above the lightning protector usually will be “smoked” and replaced, but the big expensive racks of equipment down in the BTS will be protected.

Matt Gauvin is the area product manager for Transmission Lines North America at Radio Frequency Systems.