Lightning Protection 2 (Bob, Week 4)

June 11, 2008

This second part will cover commercial products and techniques for protecting your equipment from lightning damage even if they are still plugged in.

Review
First the good news. Lightning strikes are comparatively rare here and up and down the West Coast compared to just about anywhere else in the United States.

But...
Lightning can damage your equipment even if it doesn't strike your antenna. It can come in through the power lines, the phone lines, weather station connections and even the ground.

The easiest and best way to protect your equipment is to disconnect it from any lines that connect outside your house. But if you want to be able to keep it plugged in there are products that can help prevent damage. They aren't foolproof but considering the low incidence of lightning strikes you can expect near you it may be all you need.

The General Idea
What you want to do to protect your equipment is to have any electrical spikes caused by the lightning to pass directly to ground without coming into your equipment. I am going to present a few products and techniques but these are by no means comprehensive or definitive. In other words, don't accept this as the best information. I hope to give a good start and expect you to do your homework for your set up.

The first thing you need is a good ground. This should be, the same as your RF ground. A good ground makes as much contact with the earth (dirt) as you can practically make. One good way to make a ground is to have several copper rods spaced several feet apart connected by a heavy copper strap. Another benefit to living in this area is that our soil is mostly clay after you get below the first few inches of topsoil. This is bad for gardeners but good for grounding. Clay has the lowest resistance (technically resistivity) of the common soil types.

Inside the shack, for lightning protection it is very important to have a single point to ground all of your equipment. In the RF ground segment I talked about using a copper strap or pipe. I still think these will serve but an even better solution is a large copper plate that you can directly attach your lightning protection equipment to. Whatever you use, you must then have a low impedance path to ground. The idea is to have the easiest path for the lightning or surge to take be directly to the earth outside your shack. A good choice for the connection between your single point ground and the earth is a 1 1/2 inch flat copper strap. You could even go with a wider strap for lower impedance and better protection.

Connected directly to the single point ground should be your lightning/surge protection equipment.

I am by no means an expert and this is a subject open to great debate so take my recommendations as just one opinion based on reading some of the more recent articles.

For AC power protection you have two options, one is to protect your entire house at the circuit breaker. According to a recent QST article, you can do that using MOV's for about $500. Another way would be to have the protection only for your gear by having a surge protector on the one power line that powers your gear. Powerstrips with built in surge protectors won't do much against a direct or near lightning strike.

For the COAX coming in, a poplular choice is one of the Polyphaser products. The B50 series are appropriate for amateur radio. These are gas tube devices and are said to be better than the spark gap type for newer equipment. The idea is that the old separate component and tube gear was much more resistant to surge damage so a spark-gap protection device would be sufficient. But with today's gear you need something that will redirect the energy to ground allowing less to get through to your sensitive gear.

Don't forget your other connections outside the shack: phone lines, gps, weather station, etc. All will need to be protected or disconnected to ensure the safety of your gear.


Some links:

Polyphaser's Ham Section

PDF Articles
Lightning Protection for the Amateur Radio Station -- Part 1 QST June 2002
Lightning Protection for the Amateur Radio Station -- Part 2 QST July 2002
Lightning Protection for the Amateur Radio Station -- Part 3 QST August 2002

Polyphaser Technical Article for Ham Radio - lengthy and informative article considering they want to sell you their products.

ADDED AFTER NET
Here is a great link that I found with lots of good information. I am adding it particularly at Lee's request because it shows relative resistivities of different soil types.
OH5IY's Lightning Protection Page