You're grounded!

Communications News, May, 1998

Advances in chemistry save transmitting antennas and computer equipment for lightning damage.

One powerful thunderbolt of lightning can split an oak tree in half and start it on fire, so it's possible to imagine that this same lightning strike hitting a giant telecommunications antenna can fry expensive radio equipment. An engineering firm in New Jersey had to deal with this problem head-on for a cellular phone company in New York.

The cellular phone company was in constant danger of ruining expensive receivers, transmitters, and computers--equipment totaling in the millions of dollars--due to the threat of lightning strikes. The site had three transmitting antennas and six receiving antennas on a mountaintop in lower New York state, near Harriman. Whenever there was a thunderstorm, they would get struck by lightning.

"It's well known that large towers are very good lightning rods. For example, the towers near Harriman were not only getting hit, but they were sustaining a lot of damage to the equipment inside, which is a good indication that there was a grounding problem," says electrical engineer Kevin Leary, managing director of The Avoca Group, L.L.C.

The Avoca Group is an engineering planning and consulting firm in Watchung, N.J. They are involved primarily in engineering consultation, design, and planning for the construction of telecommunications systems.

To solve the problems at the Harriman site, the first thing Leary did was to go out and test the existing grounding system. The system was made up of conventional ground rods installed in drilled holes in solid granite rock. Leary discovered that the original construction company drilled holes in the rock to put in the ordinary rods. The holes were then filled with some type of material that washed away over time, leaving loose rods rattling around in open holes. The ground resistance was very high at 50 to 60 ohms. After taking measurements of the rocky soil, Leary sent the information to a company that specializes in grounding systems.

"We told them that we had a real problem here since the soil was so rocky. We usually have at least some kind of soil and ground cover to work with. But this was basically solid granite," says Leary.

"Plus, we needed to be able to re-install rods with the least amount of onsite work, because it was such a steep, mountainous area. Lyncole, the company we use for grounding systems, was able to evaluate a very difficult site situation and find an economical, efficient solution."

Lyncole Industries has been developing and supplying precision grounding systems since 1968 from headquarters in Torrance, Calif.

Making an excellent ground is the key to squelching problems before they occur, and to keeping expensive and sensitive transmitters and receivers operating flawlessly. Since every facility is built on a site with different soil conditions, no two grounding grids are similar. So analyzing and interpreting soil conditions are extremely important in designing a precision grounding system.

An effective grounding system should be more than just a copper pipe attached to a piece of wire. For example, Lyncole starts with a high-quality, two-inch-diameter copper tube with an exothermically welded pigtail. Breather holes are drilled at the top to bring in moisture, and weep holes are placed along the length of the tube to form electrolytic roots. The tube is filled with Calsolytea, 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 called Lynconitea.

Over time, the Lynconite becomes very dense, adhering to the rod surface and creating an excellent conductive medium with the surrounding soil. The Lynconite has a resistivity of 2.5 ohm/meter, which--in conjunction with the electrolytic solution inside the pipe--increases the overall effectiveness of the system. This electrolytic grounding system improves performance over time and provides a seasonal stability static systems can't match.

The cellular company ended up drilling four new holes before installing Lyncole XIT rods in the 100 x 100foot area. Next, they notched a "V" in the granite, placed the ground lead wire in it, then used a concrete material to keep it in place.

Leary found that a benefit of using the Bentonite backfill that Lyncole supplies is that over time it retains moisture and is not as likely to wash away, so it fills in the cracks and stays put longer than ordinary fill.