Re: Lightning Protection


B C <k9wis@...>
 

Interesting about the ground differentials..several years ago I saw a storm approaching and had time to completely disconnect my radio from the antenna system and I unplugged the power supply..As I was walking out of the shack there was a flash and kapow behind me..Lightning hit the road in front of my house, and destroyed the radio, my garage door opener and all my phones..The only connection I had to my radio was the ground wire.

Brian K9WIS
---- Jerry N9AVY <n9avy@sbcglobal.net> wrote:

This showed up a few minutes ago on local club reflector and I believe it's a worthwhile read.  Dale is an old friend who move from IL (my area) out to Iowa many years ago. Before he went to work for Collins, he worked at designing RF shielded booths for testing radio equipment - lot of copper screen !

If you have outdoor antennas, I think you should read this (especially those in Florida "the lightning capital of US).

Jerry  n9avy

Everyone on this thread:

I  can not help but throw in some comments on this most important and necessary aspect of ham radio operating.  I'll try to be brief, but please bear in mind that there are a lot of aspects to this seemingly simple task that deserve some serious consideration, particularly as regards lightning safety.

First, I strongly suggest that all persons in need of installing and running transmission lines go out and buy, beg, or borrow a copy of Grounding and Bonding for the Radio Amateur, by Ward Silver, N0AX.  This ARRL book was released early last year and discusses many safety aspects of antenna and radio station grounding, including lightning protection.  Full disclosure: I was one of the reviewers and contributors for the book.

Now, to the topic at hand.  Way back in 1976, which was when I moved into my Crystal Lake house, I committed many of the very installation errors (out of ignorance) that I now fight hard to get hams NOT to do when putting in their installation.  I was a rooftop antenna farmer at that time (located in Coventry West, not far from Crystal Lake South HS) and I brought all of my radio coax and TV antenna cables inside via roof-mounted feed-thrus, then fed the cables down to the attic and inside the walls to various destinations within.  It was the perfect set-up for creating what I have since termed the "Kingsford Effect", so-named for the possible conversion of a wooden structure into a material used for outdoor cooking.  I grounded the antenna masts and roof tripod supports (2 of them) via #8 wire run on the roof and dropped down to a ground rod at the back of the house.

There are all kinds of ways to actually bring the cables into the house.  The actual approach taken by any given ham is largely the result of preference, cost, and ease of installation.  My  issue is that NONE of these approaches are safe unless lightning protection is included as part of the installation package and all protectors are properly grounded.  I will also keep this discussion limited to those installations having no more than 3 or 4 coax cables and maybe 1 rotator or remote RF switch control cable. 

For those using the "drill hole, install pipe, pull cables, and pack to preclude insects" approach, all you need to do is sink an 8 foot ground rod just outside the wall hole and place one of the readily available multi-protector mounts onto the top of the rod.  That effectively grounds and protects those cables outside of the house.  You may have to get inventive if you also need to mount an 8-line control protector for a rotator or remote RF switch.  (What, you were not planning to protect the switch?   Trust me when I say that if lightning gets onto the RF cables, it will almost surely couple onto the unshielded control cables, too.  The rotator or switch might get zapped, but you do not want lightning energy coming along that cable and into the shack.)

Next, and this is VERY important:  you MUST bond that ground rod to the equipment in your station AND you must also bond it to the electrical ground of your AC service panel.  (Yes, allowable as an Auxiliary Ground per the NEC.)  The reason: failure to bond all of the shack equipment together and failure to bond the station ground to the AC power electrical service panel ground allows a very severe voltage differential to develop during a lightning strike.  It is that differential that causes so much damage to equipment in the shack and in the house. Also, the power panel should be equipped with a while-house surge protector.   

Next, please note John's comments below about having a grounding type of switch in the shack for his coax cables.  I discovered that many DXers use a similar scheme here in Iowa when I addressed the Eastern Iowa DX Association on the topic of lightning protection in October, 2016.  Consider this:  by using such a switch as the sole means of grounding and protecting the coax cables, you are allowing the lightning energy to travel all the way into your shack and right onto your operating desk or table.  Is that what you REALLY want?  These types of switches are fine as follow-on protectors when external protector for each coax line are installed outside the shack or house.  Their most useful function is to reduce induced currents in the cables that may occur in the run from the outside protector to the shack equipment.  After all, that cable "looks" like a conductor to close-by energy currents.

Finally, I told the EIDXA that I can not endorse the MFJ (and any similar feed-thru entrance panels) that are sold for use with windows or in eaves.  Why?  Take a careful look at what they offer.  Assuming that the owner does actually attach a proper (AWG 4 or 6) ground wire to the panel, the coax cables that attach to the panel via the provided feed-thru coax connectors will have their outer shields grounded, but no protection to the center conductors.  Fortunately, that problem is rather easily fixed if a coax protector is installed on each line just to the outside of the window or eave panel.  So, for those who chose to use on of these panels, do not forget to install the protectors on it.

Now, for the kicker on these panels: have you noticed the adjustable feed-thru clamp that lows you to pass a rotator cable connector thru the panel?  OK, you pass the connector thru and close the clamp around the cable.  So?  You have the same problem as was discussed for the wall holes.  Bottom line: there needs to be a multi-line protector just outside the panel for that control cable.

Yes, I know that putting in the protectors and proper grounding takes time and costs money that you would prefer to put into rigs.  I get that.  I did my design and installation out here way back in 2000.  At today's prices for the roughly 18 cables I installed, the protectors, ground rods and #2 wire, and the weatherproof entrance boxes I used would cost around $2500 to $3000.  Was it worth it?  Look at it this way: when I moved out here in 2000, I had been hamming for 38 years.  I had ZERO lightning hits on my antennas in those years.  Then, I got hit 2 years in succession: 2008 and 2009.  The 2008 had the extra thrill factor of me holding the mic in my hand of the radio whose antenna got hit and talking (passing emergency traffic)..  Net result: ZERO damage to me or any equipment in my shack or house..  Yeah, it was worth every penny.  Antennas and coax cables on the tower got blasted to bits and one coax protector was blown up internally..  Everything on the tower should be considered as expendable.

So, lots of great ideas so far on how to get thru the wall.  I hope everyone will add in the safety aspects of lightning protection and proper grounding to their installation ideas.

73, Dale
WA9ENA
Former MCWA member, now in Monticello, IA 
Retired EMC engineer from Rockwell Collins

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