where to put the surge protector?

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by K6XRA, Apr 27, 2019.

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  1. WA7PRC

    WA7PRC Ham Member QRZ Page

    When I erected my tower, I took a hard look at grounding. Aside from the what my PE wrote about grounding the tower itself, I looked at NEC requirements. Because lightning currents are mostly in the MF to lower HF region (about 1 to 10 MHz), I resolved to use a ground bus near the rod:
    [​IMG]
    (click for bigly image)
    The 2" x 0.032" copper strips run a foot or so to the shack ground rod. The tower and its four ground rods are to the right. A 4 AWG solid conductor bonds the rods to the electrical service ground about 50' away. This complies with NEC, and effects a reasonably low-Z path to ground. :)

    Tom W8JI (in GA) has stated that his several TALL towers each receive multiple direct lightning strikes/year. And, he has yet to suffer any significant lightning damage. He's either VERY lucky or, he's doing something right. :)
     
    K0UO, N0TZU and K6XRA like this.
  2. K6XRA

    K6XRA Ham Member QRZ Page

    This discussion is being helpful, and I am considering some new ideas for my actual installation, which has no antenna, ground wires, coax or radio installed yet. We did put in a bunch of ground rods today. ;-)
    But it really isn't obvious where to put that surge protector, in my setup.
     
  3. K6XRA

    K6XRA Ham Member QRZ Page

    That's an awesome setup! My single antenna with a single radio situation is more like a TV antenna than this. ;-)
     
  4. K6XRA

    K6XRA Ham Member QRZ Page

    Are there surge protectors somewhere in this setup? Looks just like shield grounds only?
     
  5. WA7PRC

    WA7PRC Ham Member QRZ Page

    My point was to keep the distance to ground (and the AC impedance) short.

    No "surge" protectors, just bulkhead adapters (Amphenol pn 83-1F, et cetera). Consider this... the voltage produced by a transmitter is yuugely more than what would destroy a receiver frontend. However, a so-called "protector" has ONE breakdown voltage point. Then, the best protection is good insurance.
     
    W6KCS likes this.
  6. K4EI

    K4EI XML Subscriber QRZ Page

    I won't reprise everything I wrote in my post in the other thread. But a few quick thoughts...

    Not to be provocative, but in your use case - a small vertical antenna directly mounted to the roof of your house - the "lightning protection" that you almost certainly envision, a direct strike to your antenna, isn't there. Regardless of where you physically place your lightning arrestor.

    A direct lightning strike introduces physical effects such as heat and explosive atmospheric compression in addition to its electrical effects. And those electrical effects are so vast and so sudden that they typically overwhelm the orderly and predictable flow of electrons that we usually imagine. A lightning strike on your house or your antenna is likely to take multiple paths to ground.

    Which doesn't mean you should forgo a lightning arrestor. You should still install one, to protect against induced currents from a non-direct strike. Just realize the limits of what such protection can give you.

    Your objective is to keep any large, induced currents outside. And you're doing it in a situation where voltage differences can be very large, even across relatively short distances. Arcing and flashover remain possible until those voltage differences dissipate.

    You need two things: your lightning arrestor must have a very robust ground, and that ground must be bonded to your house's main service panel ground.

    Best practice is to physically mount your lightning arrestor directly to your ground rod - even if that requires a few extra feet of coax to get there. The current shunting that you're looking for happens at the arrestor itself. It's critically important that impedance from there to ground be as low as you can possibly achieve. Mounting directly to your ground rod gets you that. Mounting anywhere else begins to walk you away from it. Just do it.

    Any coax on the other side of the lightning protector doesn't matter. Presumably, hopefully, it's "protected." The only thing you're dealing with at that point is loss, a much less worrisome issue.

    A lightning arrestor in your situation is considerably less important than if you were running a long wire antenna, or a tower-mounted antenna. But it's still a good thing to do.

    FWIW, I have a similar situation... my 2-meter antenna is a Hustler G6, mounted to my roof. I have no illusion that the lightning protection on that antenna is as necessary or effective as it is for the three long-wire HF antennas that also come into my shack, but you do what you can, right?

    Mount your arrestor on your ground rod.
     
    W6KCS and KA0HCP like this.
  7. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    I now agree that the best location for the ADU is at or very near the ground rod, after having done a "napkin" Ldi/dt calculation for the proposed lengths at the OP's house. However, as K4EI points out, in this particular case it probably doesn't really matter too much.

    It's interesting to consider what threats our typical amateur and household systems are mostly exposed to and should withstand. Rather than a direct or glancing side strike, in my opinion the far more likely scenario is static buildup and excessive currents and voltages induced from nearby lightning strikes, and possible ground "step" voltage difference between the AC service entrance ground rod and the radio system ground rod. Also, lightning currents and voltages traveling along power lines into the house.

    Household ground systems and most amateur antenna grounding is not designed to deal with the currents from direct strikes anyway, regardless of ADU location. Better amateur tower installations might be designed for direct strikes, and most commercial radio and telecom installations are.

    Direct induction from a very close strike could still be very damaging even with a favorable ADU location and short ground wires, because the feed line inside the house could acquire a large induced current and voltage simply because of its length and orientation to the strike. The same thing could happen with house AC wiring and other wires and metal pipes.

    So in my opinion there is a practical limit to how much one can do with the ADU and ground system. Adhere to the building codes, and do the best you can with the situation you are dealt. Unless of course you are fortunate enough to build your own house from the ground up with radio and lightning protection in mind.

    Insurance is for the rest!
     
    W6KCS likes this.
  8. K9STH

    K9STH Platinum Subscriber Platinum Subscriber QRZ Page

    XRA:

    B is much better than A.

    Lightning will not reverse direction. With B, the strike energy will continue downward, to ground, with very little, if any, going upward to the equipment. However, with A, the charge can split, or most of the charge can travel, down the angled connection to the equipment thus producing damage.

    All ground conductors need to continue in the same direction with no reversals and with only gradual sweeping curves in the conductors. Definitely NO right angles!

    To put it bluntly, good grounds are usually not "pretty"!

    Glen, K9STH
     
    AJ6O likes this.
  9. N0TZU

    N0TZU Platinum Subscriber Platinum Subscriber QRZ Page

    How are the cables routed from the antennas that go into the top of the enclosures? Are they on (or in) the ground, then come up along the wall and over to the enclosures?
     
  10. AJ6O

    AJ6O Ham Member QRZ Page

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