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To accomplish this required several integrated steps. In addition to upgrading the grounding system, a lightning protection system and surge suppression devices had to be installed.
On the radio tower, three 48-inch lightning air terminals were mounted so they were higher than the highest projections such as warning lights or antennas. Lightning down conductors were run along all four legs of the tower and bonded to a buried grounding ring.
On the equipment building, six 48-inch lightning air terminals were similarly mounted and bonded to a separate buried grounding ring. The tower and equipment building grounding rings were then bonded together to prevent differences in potential, that could have lead to secondary electrical arcing and personnel safety issues during a strike.
For the same reason, a surrounding metal perimeter fence and its gate were separately bonded to the grounding rings, so all structures would maintain a similarly low grounding resistance and equal potential. This provided a single reference grounding system. Post project testing showed a reading of 3.8 ohms, satisfying the below 5 ohm target.
To protect against electrical surges in the tower-mounted coax cables, surge protection was installed on the coax cable leads. On the AC power supplying the equipment building, a heavy-duty surge protector was installed to immediately shunt any lightning or utility-caused over-voltages to ground.
"So far total site lightning, surge, and grounding protection has eliminated the problems we had with lightning strikes. Through the worst of lightning season, we've had no equipment loss due to lightning and are maintaining full communication capability. At this rate, we'll achieve ROI in about two or three years, so we can redirect our resources toward better goals than troubleshooting and fixing lightning damage," Franklin notes.
"The new system makes things easier for everybody and helps us stay at full operational readiness and training capacity," adds Franklin. "Since pilots, air traffic controllers, and ground support have all their communications channels available to them even in bad weather, there's been no need to resort to 'work around' communications channels." With the success of the project, NAS Key West is now looking into total site electrical protection at other facility installations.
