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Dialight Beacon as a lightning rod
If there was any doubt as to how a Dialight LED beacon would take lightning strikes, the following should clarify the issue very well.
On February 21, 2001 our tower crew installed the first LED beacon in the Nashville Tennessee area on the 1235 foot tall WKDF tower. Though the Dialight beacon is sold as a direct replacement item, and its mounting flange is of the standard L864 bolt pattern, the housing of Dialight's D854-A11-001 is of a greater diameter than the traditional incandescent beacon, an item it's likely to be replacing. The existing lightning rod system atop the WKDF tower wouldn't allow the installation of the new device. The increased girth of the LED beacon would only allow it to get within six inches of the mounting plate which was an integral part of the original lightning rod system before the rods stopped it. As a result of this we were forced to remove the existing lightning rod assembly.
The managing engineer of the site quickly ordered a new lightning dissipater from ERI quickly so that we could provide protection for his new purchase but before we could install it one of the community users of the top multi-bay FM antenna purchased a new transmitter and was suddenly unable to switch to the standby antenna when crew members were on the very hot stick. By this time the beacon was working well and had survived, apparently unaffected, numerous lightning storms. Little did we know.
In late June of 2003 the beacon apparently went dark and was reported out. The community user of the antenna placed greater effort on getting their new transmitter installed and we awaited a go ahead for the repair of the beacon. We had no clue as to what was wrong with the unit. In fact I noticed one night while working on a tower about eight miles away I was able to see that the top beacon on the distant WKDF tower actually seemed to be flashing though not as bright as the others. It turned out that only of the two hemispheres of 360 LED's each had failed.
Finally everything was set for an attempt to repair the beacon. Could it be a fuse? We had no clue. The Dialight has two glass fuses, one in each of the two power supplies. The managing engineer had received enough parts to replace all of the electronics. Thus, on August 14, 2003 we climbed and rigged the tower for the attempt at repair.
Upon reaching the beacon, the crew was faced with evidence of massive lightning damage. It was now obvious that the Dialight LED beacon is not happy serving in the dual capacity of beacon and lightning dissipater. As the uppermost metal on the tower it was pock-marked with about forty holes and looked as one engineer commented, "like someone flew over in a helicopter and fired a shotgun straight down on it." Our only choice was to lower it to the ground for an attempt at a rebuild.
The top of the beacon is aluminum. It screws into a support, also of aluminum which consists of two telescoping rods nested into each other. The base of the support is a flange which is screwed into the beacon's base. The base of the beacon is also an alloy and it is assembled and then screwed together. The lightning strike to the top of the beacon caused the screws in the base of the support to vaporize. The strike also caused much distress in the base assembly screws. In my opinion, the beacon would have probably come closer to surviving had the top been electrically bonded to the base of the beacon and the beacon then bonded to the tower. The base of the beacon is painted, and we didn't scrape paint before installing. Evidence is everywhere showing where the lightning found the weak points on the painted bottom to make its exit to the tower.
The plan is to rebuild this unit, of which, one hemisphere, power supply and the Lexan lens seem to be all that remains. I'm in the process of trying to determine the parts that will be necessary for this undertaking. I hope to have a new Dialight beacon, hopefully the newer, half-height delivered by early next week so that we can get the tower's top beacon working again.
As a final note however, I must reiterate that the Dialight LED beacon makes a very poor lightning rod. We've already installed the replacement rods on the WKDF tower; now all that remains it to replace the beacon. When rebuilt, the original beacon will occupy a spot much closer to the ground.
John Hettish
Middle Tennessee Two-way Inc
615-890-6685