Care to hazard a guess on the percentage of facilities (radio/tv, two-way) that aren't done right?
A few years ago this happened near here - a radio personality wearing headphones taken to the hospital following a lightning strike to the tower outside the radio station. Chuck WB2EDV ----- Original Message ----- From: "Eric Lemmon" <wb6...@verizon.net> To: <Repeater-Builder@yahoogroups.com> Sent: Sunday, August 01, 2010 11:42 AM Subject: RE: [Repeater-Builder] OT- Dispatcher injured by lightning strike > Whenever I read a report like this, I have mixed emotions. I am surprised > that the injury occurred, which is impossible if the facility was properly > designed and islanded in accordance with numerous standards, including > NFPA > 70, NFPA 780, and the Motorola R56 Manual. I am also angry that an > official > issued the statement that "...the communications system, including its > 400-foot radio tower, are grounded in accordance with industry safety > standards." That official, and the idiots who designed the communications > center, should be fired and/or brought up on criminal charges. > > The key to a safe installation at a location with an on-site tower is to > ensure that all utilities pass through a "window" where a common ground > reference exists. Ideally, the tower should be right next to the > facility, > so that the same ground reference is used for both. The power transformer > that feeds the control room should be in that room, not hundreds of feet > away, and the secondary neutral of that transformer should be bonded to > the > same ground that is used by the telephones, radio system, cable TV, > satellite system, and raised-floor supports. If executed properly, the > design of the control room creates a Faraday Cage within which all > occupants > are safe from injury due to GPR (Ground Potential Rise) from a nearby > lightning strike. Likewise, all the electronics within the control room > are > protected against surge damage. > > It is obvious from the news report that the dispatcher was injured because > her headset was at a different potential from her body. The GPR resulting > from lightning striking the tower led to thousands of volts difference > between the radio control system (the headset) and the floor and counter > in > the control room- and the chair she was sitting in. It is also obvious > that > this difference in potential could not exist if the tower and the adjacent > control room were grounded in accordance with industry safety standards. > Some common sense and credible engineering skills are essential elements > in > a proper control room design. > > Many moons ago (late 60's), I was Chief Engineer at radio station WLRW, a > 50 > kW FM station at Champaign-Urbana, Illinois. During my watch, the station > control room was relocated to a building next door. It was my job to > supervise the cabling installation within the building and to the > transmitter at the base of the tower, which was just over 100 feet away. > All of the remote circuits and network feeds came through a grounding > window > that was common with the power and the tower grounding system. I remember > arguing with the Illinois Power foreman about how we needed a separate > transformer to power the station, and it had to be installed right at the > side of the control room and not in a vault several hundred feet away. > The > value of designing the entire installation to comply with established > industry standards and sound engineering practices was proven many times, > when the tower was struck by lightning during a storm, and no damage or > injury occurred. Although the station was on automation most of the day, > we > had live talent from late afternoon to early morning, and at least one > lightning strike occurred while on-air talent was at the board and wearing > headphones. The lights blinked, but the board operator felt nothing and > the > show went on. > > 73, Eric Lemmon WB6FLY
