I want to reiterate some of Moe’s comments about lightning he shared on our training net Sunday last as some missed it, and expand on the topic for SKYWARN or even search and rescue operations.
He pretty well did a risk assessment; in our area we have about 50 lightning strike days a year. And that takes us to our structure height (tower or mast). If you have a 30 foot tower or so you can expect a direct hit every 2-3 years; if you’re blessed with a 100 footer, once every other year. So it’s not if…it’s when will you be struck. Your grounds will not bypass the lightning to ground and save your equipment, but it will provide a path to ground and maybe not thru something else (like you, though I would not want to be in the room). It will raise the potential difference of the connected systems to several thousands of volts and expose the components to conditions not even thought of in their design. The smoke will come out, probably lots of it. Some of the old ideas of “prevention” are just not realistic when you stop and think it through, such as disconnect the coax and lay it on the floor, or worse – put it in a jar on the work surface. The lightning just crossed over a mile of air to get to the ground… do you really think three feet of carpet or the thickness of a glass jar will withstand a strike of 300,000,000 volts and over 40,000 amps creating temps of over 50,000 degrees?
The best solution? Disconnect the lead-in wire before it comes in the house, out at the tower. And don’t forget the rotor cable; a path is a path even at 16 gauge wire.
Now that’s a rough summation, but let’s take it a step further for our outdoor weather enthusiasts.
The National Lightning Safety Institute has the following recommendations: “Preparedness includes: get indoors or in a car; avoid water and all metal objects; get off the high ground; avoid solitary trees. If caught outdoors during nearby lightning, adopt the Lightning Safety Position (LSP). LSP means staying away from other people, taking off all metal objects, crouching with feet together, head bowed, and placing hands on ears to reduce acoustic shock.” Also consider these… It’s easy to determine when to take shelter. If you hear thunder, the associated lightning is within 8 miles. Suspend activities, allowing sufficient time to get to shelter. A good lightning safety motto is: “If you can see it (lightning), flee it; if you can hear it (thunder), clear it.” If you feel your hair standing on end and/or hear “crackling noises” you are in the lightning electrical field. If you are outside your vehicle stay away from power poles, fences, high-mast light poles, metal bleachers, electrical equipment, mowing and road machinery. Fully enclosed metal vehicles are safe shelters, as well as other all-metal mobile equipment. This includes airplanes, buses, vans and construction equipment with enclosed metal cabs, provided the “outer metal shield” is fully intact. All windows must be rolled up and people inside should avoid touching all objects that penetrate from inside to outside (e.g., radio dials, metal door handles, two-way radio microphones, etc.). I highlighted the references to radio – if you’re out spotting pay attention to this. Maybe a HT with a short antenna is good tool to keep on hand while mobile and lightning is near.
So, be aware of your surroundings and realize this is not a walk in the park. Use some common sense and let’s all be safe in this stormy weather season. Our communities are counting on you to provide good information, not become a news story with a sad headline. Thanks to Moe for researching lightning for the net and to all of you for your dedicated service to Grayson County and the surrounding area.
73
Rick
K5ECX