[Antennas] Lightning protection for elevated lead-ins

[Jack Painter]

Hi Dave,

Please abandon all thoughts of bringing any elevated feedline into your home
directly. This is so dangerous and nearly unprotectable that it could render
you uninsurable in the event of a casualty.

That is unless you can afford total isolation of your *entire* shack from
all other ground and power sources, and have *everything* bonded only to the
feedline coax-shield path to ground. This would require HV isolation
transformers or fiber-optic connection of the center conductor to your
equipment, and HV isolation transformers on all three (line, neutral and
ground) AC power connections. AC wiring in the walls would have to be
covered in bonded metal conduit.  Out of the realm of reality unless the
home was designed for this during construction.

I recommend using low-loss feedline to an 8' earth ground rod first, ground
the coax shield there, then install a coax arrestor at that ground level.
Then you can safely bring the feed back up into your second floor, providing
you do add the shortest possible bond from any system-ground rod to your
shack. This will require at least 6" wide copper strap ( I would use 12")
but you can paint one side of this to match your homes exterior. This is
your bonding conductor, and you can use the 3" strap to bond all gear inside
the station from that. Don't forget a buried bonding conductor from the
antenna ground rod and shack's ground rod to the home's service entrance
ground rod.  Back to the roof- the antenna mast is an air terminal
(attachment point for lightning) and must be grounded at both opposite ends
of the home to a minimum of two 8' ground rods at each end. Yes one of those
pair of ground rods at each end should be your service entrance ground rod.

Leaving equipment connected to both the antenna and AC power during storms
requires the very best of all-path protection. This means from direct
strikes, near-field lightning, Ground Potential Rise and AC power surges.
This is regardless of where the shack is located. If your mast/antenna has
at least #2 solid wire conductors to at least two 8' ground rods in good
soil and at opposite ends of the home, the structure is protected from a
direct strike *at that one point*. Air Terminal conductors and down
conductors should be secured directly to the roof system and exterior walls
with no standoffs.

What if you can never manage to make that 12"-strap bonding connection from
shack to ground system? The equipment will still be protected as long you
disconnect AC power before a storm. And, as long as nothing conductive and
no person comes within 1' of that equipment with its feedline connected and
AC disconnected, *it* should be fine. Not sure your wife or kids will be
fine with that concept, since omitting the shack bonding elevates the
touch-hazard from "possible burn" to "possible death".

73,
Jack Painter
Virginia Beach VA

----- Original Message ----- 
From: "David Kelley" <dkelley at bucknell.edu>
To: <antennas at mailman.qth.net>
Sent: Thursday, November 18, 2004 12:58 PM
Subject: [Antennas] Lightning protection for elevated lead-ins


> A question for the lightning protection experts:
>
> I am planning to install a 6-m/2-m Yagi combo on the roof of my
> house, and I would like to bring in the coaxial cables near the peak
> of the roof, which is approx. 25 feet above ground.  This is necessary
> to minimize the lengths of the lines and therefore the loss, because
> my shack is in a second-floor bedroom.  I would like to install a good
> measure of lightning protection for the system.
>
> I know that the "single point ground" is the first commandment of
> lightning protection; however, in my case the telco and AC mains
> enter the house right at ground level.  Would it be reasonable to
> install a copper panel near the peak of the roof and run a 3-inch
> (or so) copper strap down to the ground rod next to the telco/AC
> entry point?  The length of the strap would have to be around 30 feet.
> I realize I would have to improve the current grounding system at
> ground level to make it effective for lightning protection.  I would
> install coaxial surge/impulse protectors on the copper plate at the
> roof peak.
>
> Can I run the strap right up against the edge of the roof, or should
> I use stand-offs to space it an inch or more?
>
> Thanks for any thoughts or suggestions.
>
> 73,
> Dave
> NB4J