Lightning Arrestor

[Patrick_]

I just found a Monitenna on closeout, and I'm going to be setting it up. I just need to buy a ground rod and some ground wire at Lowes. My question is, do you recommend I also purchase a lightning arrestor, or is it not worth it? During storms, or periods not listening to my scanner, I would always unplug the cable. Is this enough?

I've read here that many think a lightning arrestor not worth it, as they usually just burn out, anyway. I guess my main question is, would it be dangerous to simply unplug the coax when not in use?

 

[N_Jay]

I just found a Monitenna on closeout, and I'm going to be setting it up. I just need to buy a ground rod and some ground wire at Lowes. My question is, do you recommend I also purchase a lightning arrestor, or is it not worth it? During storms, or periods not listening to my scanner, I would always unplug the cable. Is this enough?

I've read here that many think a lightning arrestor not worth it, as they usually just burn out, anyway. I guess my main question is, would it be dangerous to simply unplug the coax when not in use?

\Buy the lightening arrester for lots of reasons.

1) easiest way to ground your coax.
2) shunts static and induced voltages from nearby lightening making your equipment safer.
3) may provide some basic safety shunting in a real strike
4) is required by most electrical codes and not having it may invalidate your insurance.

 

[Patrick_]

Ok, thanks. Now, could I use a coax ground block, instead of a lightning arrester?

 

[N_Jay]

Ok, thanks. Now, could I use a coax ground block, instead of a lightning arrester?

Does 1 and 4

 

[kb2vxa]

Hi Patrick and readers,

Most definitely install a lightning arrestor but it must meet NEC specifications. That means run the coax down as close to the ground as practical and put the arrestor there, then run it to where it must go. Use a minimum of 6AWG solid copper wire bare or insulated doesn't matter, run in as straight a line as possible without sharp bends or kinks to the earthing rod and use the approved bronze connector. The rod must be 2' from the foundation wall and may be entirely buried so nobody trips over it or the wire or lawn mower blades go flying.

Note; Do NOT use aluminium "antenna grounding wire" because it corrodes, stiffens and deteriorates in just a few years and becomes useless. I removed a ham antenna grounded with it for a widow and the wire fell to pieces in my hands. It doesn't meet Code for that reason, labeling it with the word "antenna" is a loophole in the law.

"I've read here that many think a lightning arrestor not worth it, as they usually just burn out, anyway."

If it doesn't burn out it hasn't done it's job, that's why arc plugs are replaceable.

"I guess my main question is, would it be dangerous to simply unplug the coax when not in use?"

Yes, without diversion to ground lightning will arc and find ground inside the house and you know what THAT means. Never trust the ground 100% which means >also< disconnecting the coax breaks an alternate path to ground through your equipment and the house wiring, maybe even YOU.

"Now, could I use a coax ground block, instead of a lightning arrester?"

The Code only requires the coax shield to be grounded, CATV service drops are grounded this way. Six of one, half dozen of the other, it's all the same to a one legged duck.

 

[Patrick_]

Ok, do you recommend I buy this arrester (http://www.homenetworkingdepot.com/...e/tii_protector/tii_frame.html?=212FF75F.html) or this arrester (http://www.hyperlinktech.com/web/al-ffff.php)? The benefit to the former is that the gas tube is easily replaceable; however, it says it accepts 10AWG wire or smaller. I'll be buying at least 6AWG. Could this be a problem? Would it be ok to slightly flatten the wire?

 

[kb2vxa]

Go back and read the last paragraph, then apply common sense. As for the wire question, you can always solder an inch of 10 to the end of the 6 using a cable splice, NOT a pigtail splice.

 

[n5ims]

What's the feeling about 'lightning loops'?

With all the talk about lightning protection, I haven't seen any mention of 'lightning loops'. These are made by making a loop in the coax (two to three turns, generally) between the lightning arrester and radio. This is a secondary protection only, and used only as a suppliment to the primary grounding and lightning protection.

This was taught to me by Howard Griffith, who was a long time broadcast engineer and UHF TV transmitting antenna designer. The theory is that the inductive current will hinder the current flow for the lightning, causing it to prefer the more direct path to ground through the lighting arrestor or ground block.

I use them on my coax runs (as well as phone and network cabling). I have also seen it used by some cable tv installers.

 

[kb2vxa]

Hi IMS and all,

Good point, AM broadcast towers are connected to the "dog house" or tuning house as it's properly called using soft copper tubing bent into a one turn loop about a foot in diameter. Lightning doesn't like that small inductance so it arcs across the horn gap to ground and little to none* gets into the tuning network. They're also used on grounded towers (the grounded vertical folded unipole) but only in AM broadcasting to the best of my knowledge.

I've never seen hard line looped that way on broadcast or commercial towers, probably because coax and especially hard line has a limited bending radius and conductor migration would cause serious problems especially at such high power levels. That's why special angle fittings are used making the transmission line look rather like a plumbing job.

Bending coax into a loop like that may or may not prove anything but there is one important thing to consider. The loop described above never comes less than within a few inches of itself and is several feet from surrounding objects which would be a neat trick anywhere but between the tower and the tuning house.

* Little to none on a good day. Nothing is perfect and lightning being what it is I have seen transmitting equipment turned to ashes and some rather unhappy GMs and CEs. One time I saw a weatherman reporting a severe storm do the Neutron Dance when lightning struck the tower and found it's way through the mic cord, funny as hell!

Oh well, he asked the time and we told him how to build a clock. (;->)