{"id":2741,"date":"2011-04-06T16:15:00","date_gmt":"2011-04-06T20:15:00","guid":{"rendered":"http:\/\/www.engineeringradio.us\/blog\/?p=3928"},"modified":"2023-04-30T14:23:36","modified_gmt":"2023-04-30T18:23:36","slug":"lightning-season","status":"publish","type":"post","link":"https:\/\/www.engineeringradio.us\/blog\/2011\/04\/lightning-season\/","title":{"rendered":"Lightning Season"},"content":{"rendered":"\n

The rumble of thunder this morning let me know that lightning season is upon us here in the Northeast and likely the rest of the country as well. \u00a0I used to enjoy the odd summer thunderstorm, especially the late afternoon pop-ups that cool off a hot summer’s day. \u00a0Now whenever I see lightning or hear thunder I wonder if the phone is going to ring. \u00a0Chances are good that it will not, as I invested many hours of my time and my previous employer’s money into lightning protection at the transmitter sites.<\/p>\n\n\n\n

\"upper<\/a>
upper atmosphere lightning depiction<\/figcaption><\/figure>\n\n\n\n

I go on the assumption that all tall steel towers will get struck, oftentimes repeatedly, during any particular electrical storm. \u00a0Back in the day, I took a course by Polyphaser called “The Grounds for Lightning and EMP Protection.” \u00a0It was a great primer on how to ground and bond equipment at a transmitter site to eliminate current flow, which is the cause of all EMP and lightning-induced failures. When I was in military communications, no expense was spared\u00a0as they took uptime very seriously. \u00a0Any downtime was a personal affront to the commanding officer of the unit in question.<\/p>\n\n\n\n

Lightning is DC however, it behaves more like 10 KHz – 2 MHz AC. \u00a0Therefore, lightning and EMP grounding systems need to be designed and installed to accommodate DC through 10 KHz AC voltages. \u00a0This is easily done by choosing the correct conductors, ground bus bars, and bonding systems.<\/p>\n\n\n\n

The other path lighting takes into a transmitter is through the AC mains. \u00a0Utility company high voltage primary feeds act like large antennas for lightning-induced EMP. \u00a0Fortunately, much of that is filtered out by the step-down transformers just before the building service entrance. \u00a0It is still possible, however, for some impulse voltage to make it through the transformers and into the service entrance panel. \u00a0On older tube type transmitters, this could often damage the plate voltage power supply because of the voltage multiplication factor of the plate transformer. \u00a0Oftentimes, the transformer secondary would have “holes” punched through the insulation to ground. \u00a0This is an expensive and time-consuming repair.<\/p>\n\n\n\n

I would conservatively estimate that for every $10.00 spent on lightning protection, $1,000.00 dollars worth of damage and downtime is saved.  Overall, a pretty good return on investment.<\/p>\n\n\n\n

The basics for lightning ground bonding are thus:<\/p>\n\n\n\n