You're grounded!: Maintaining a well-grounded tower site can protect your network from the elements

One powerful bolt of lightning can split an oak tree in half and start it on fire, so it's not impossible to imagine that lightning striking a giant telecommunications antenna can fry expensive radio equipment into unusable charcoal briquets.

This type of problem has affected a cellular carrier in New York with a somewhat vulnerable but necessary mountain-top tower site.

With every turn toward inclement weather, the cellular company was in constant danger of ruining receivers, transmitters and computers worth millions of dollars. The site had three transmitting antennas and six receiving antennas on a mountaintop near Harriman, N.Y., and whenever a thunderstorm passed, giant bolts of lightning struck them.

The risk of weather-related damage is something many tower owners must deal with. But for the New York company, concerns went much deeper because lightning was damaging the inside the site, according to the carrier's engineering firm.

"It's well known that large towers are very good lightning rods," said Kevin Leary, managing director of The Avoca Group, L.L.C. "For example, the towers near Harriman were not only getting hit, they also were sustaining a lot of damage to the equipment inside, which is a good indication that there was a grounding problem. Basically, it was blowing out printed circuit boards in computers and radio equipment."

Soil surveyors The Avoca Group, based in Watchung, N.J., is primarily involved in designing, planning and engineering the construction of telecommunications systems including cellular, PCS and cable TV. Such firms also help prepare real estate for transmission site construction by testing and analyzing the soil on the property.

"First we do site testing for soil resistivity to determine how good or bad the soil is for grounding requirements," said Leary. "After we complete our work, we hand it over to the client's construction contractor. Sometimes we assist in the construction process and follow up after it is completed."

To solve the problems at the Harriman site, Leary first went out and tested the existing grounding system. This system consisted of conventional ground rods installed in drilled holes in solid granite rock. His firm found that the original construction company that worked on the site had drilled holes inthe rock to put in the ordinary rods and then backfilled them with material that washed away over time.

As a result, the carrier's tower site was grounded by loose rods rattling around in open holes. The ground resistance was very high at 50-60 ohms. After measuring the rocky soil, Leary sent the information to Lyncole Industries, a company in Torrance, Calif., that specializes in grounding systems.

"We told them that we had a real problem here since the soil was so rocky," Leary said. "It was not at all the normal type of site that we work with in this part of the country. We usually have at least some kind of soil and ground cover to work with, but this was basically solid granite. The only plants growing were a few weeds stuck in the cracks.

"Plus, we needed to be able to re-install rods with the least amount of on-site work because it was such a steep, mountainous area. We had to use a truck-mounted drilling rig that would make it up the twisting, switchback road. We couldn't do any blasting, and it was heavily wooded."

Providing a proper ground is the solution to squelching problems before they occur and to keeping expensive, sensitive transmitters and receivers operating flawlessly in harsh conditions.

Because every facility site has different soil conditions, no two grounding grids are similar. This means that analyzing and interpreting soil conditions are extremely important in designing a precision grounding system.

Extreme conditions in soil moisture and in cold or heat must be taken into account. For example, a sandy site near Phoenix will need different grounding specifications than one with rich, earthy loam near Portland, Ore.

Because wireless carriers are expanding their networks to deliver reliable local, regional and even national coverage, they are bound to face a wide variety of grounding requirements.

Solid ground An effective grounding system should be more than just a copper pipe attached to a piece of wire. It should be a high-quality, two-inch diameter, copper tube with an exothermically welded pigtail (Figure 1).

Breather holes are drilled at the top to bring in moisture, and weep holes run the length of the tube to form electrolytic roots. The tube is filled with an electrolytic compound that attracts moisture from the air.

The rod is then inserted into the earth and surrounded by a backfill of natural clay, according to Lyncole.

Over time, the clay becomes dense, adhering to the rod surface and creating an excellent conductive medium with the surrounding soil. The clay is non-corrosive with a pH of 8.0, and it protects the rod from any surrounding acidic soil.

The clay that Lyncole uses as part of its grounding system has a resistivity of 2.5 ohm/m, and with the electrolytic solution inside the pipe, it increases the system's overall effectiveness. This electrolytic grounding system actually improves performance and provides a seasonal stability that static systems cannot match.

The New York cellular carrier's technicians ended up drilling four new holes before installing Lyncole rods in the 100-square-foot area.

Next, they notched a V in the granite, placed the ground lead wire in it and used a concrete material to keep it in place. Leary found that one of the benefits of using a different backfill is that it will retain moisture over time and it also will be less likely to wash away.

"This tremendously improved the grounding problem at this site,"Leary said. "We got the ground resistance way down, below 10 ohms, thereby solving the lightning damage problem."

Using an efficient grounding system can save time, money and frayed nerves. Because radio frequency systems run in the millions of dollars, carriers should do whatever needs to be done to protect them.

"The savings that come into play when using an efficient grounding system are that you're eliminating down time when electronic equipment has to be repaired," Leary explained. "Also, the high cost of replacement parts for damaged equipment can be avoided,"

"Many companies think that they don't have the time or manpower to worry about installing a good ground, but this sort of thinking can get them into trouble in the long run."