Re: [Repeater-Builder] polyphaser Help

Fri, 30 Dec 2005 21:25:51 -0800

I don't know when to give up.
 
Your lightning deversion system can run straight back to your own grown rods, but your ground rods need to have a bonding conductor to the electrical system ground rod. The lower impeadence path is still to your rod, but the entire site ground potential is equal. I know around here you can be fined heavily if you don't do that.
 
Stupid question: what about the ground on your power supply? Do you cut that pin off to seporate your gear from the electrical system ground? I didn't. If you have a seporate ground system and you still have a tie to the electrical ground you have two different potentials meeting at your gear. Besides the ovious dangers, you could have several volts difference being created on your ground potentially causing other fun problems.
 
At my site, a water tower, I have the mast bonded to the steel structure of the tower (db-420 antenna), a polyphaser that's grounded via its own ground wire back to the ground rod or the electrical sysstem, which is also bonded to the steel structure of the tower. I have Furman A/C surge protection on the equipment.
 
Someone on the list that deals with big commerical sites (sears tower, etc) should let us know what is done there. I would like to hear about that having no experience with those.
 
The 800 pound gorilla is the truth, and it will do what it wants when it wants to!
 
I've been to Florida and saw a relatives house under construction. Just bond to the plastic cold water pipe! ;)
 
Awaiting my lashings.....
 
Tom
W9SRV 

Dick <[EMAIL PROTECTED]> wrote:
Roger that, Mark.

A lightning diversion system needs its own low impedance path to ground
because the huge currents involved can do strange and unpredictable
things if they get into the building's AC power.

A full threat lightning attachment has millions of volts before the air path
ionizes. Once the air path ionizes, its impedance is essentially zero
and the current during the flash can reach 250 K amps. On average, the
AC component of the lightning flash is around 125 KHz. You really don't
want that kind of energy running around the buildings AC power wiring
because there will be arcing nasties along with induced currents that can,
and probably will, fry stuff like computers, TV's, etc.

After a lot of years at Lockheed designing lightning protection for
military aircraft, I've developed a very healthy respect for the stuff.
You can sit there and calculate impedances, etc., until the cows come home,
but when lightning hits, it's still not all that predictable.

Use a DC grounded antenna and a dedicated path to a dedicated ground rod
to divert as much lightning energy as possible away from the building's
AC power system. Also, use the available braided lightning diversion cable
from the lightning rod (in this case, your DC grounded antenna). The
Polyphaser (R) will help, but a direct lightning attachment to your antenna
will most likely destroy it. But, IMHO, it's better to sacrifice the
antenna
than the repeater and associated electronics.

Lightning is like the 800-pound gorilla. It goes wherever it doggone well
pleases.

Dick

----- Original Message -----
From: "N9WYS" <[EMAIL PROTECTED]>
To:
Sent: 30 December, 2005 15:53
Subject: RE: [Repeater-Builder] polyphaser Help


I think what Dick was getting at is that the Polyphaser grounding lug needs
to have its *own* ground - separate from any other ground. If you tie the
Polyphaser to the electrical ground of the building, you're defeating the
entire purpose of having it. But then again, I've been wrong before.


Mark - N9WYS

________________________________________
From: Repeater-Builder@yahoogroups.com
[mailto:[EMAIL PROTECTED] On Behalf Of TGundo 2003
Sent: Friday, December 30, 2005 5:35 PM
To: Repeater-Builder@yahoogroups.com
Subject: Re: [Repeater-Builder] polyphaser Help

Someone correct me if I'm wrong, but putting in your own ground rods and NOT
tying them to the existing electrical ground system is a Bigger no-no. That
would be creating a second ground system for the building and creating a
potenital difference in grounds. That would be a bigger problem, and the
local codes here require a bonding conductor of some sort. You can put in
your own rods, which I agree with, but you must tie the two systems together
and make it all one ground potential. It's all about equal potential, isn't
it? If you don't get hit at all you don't have to worry about the voltages!

How about the install on a all-steel mushroom type water tower? At the
bottom the 1" threaded rods go in the ground and they are every foot around
the perimeter. Makes a great ground plane for a DB-420!

Someone please tell the cable guys to stop putting in the 4ft rods and
creating ground loops! ;)

Tom
W9SRV

Dick <[EMAIL PROTECTED]>wrote:
Whatever you do, DON'T connect the polyphaser grounding lug to an AC outlet
ground lug!!! That would bring HUGE voltages and currents into the building
electric power system and expose everything on it to disaster!!! In which
case you'd do well to carry enough insurance to replace all of the electric
and electronic gear in the building.

If you plan to connect it to the metal roof, make sure the metal roofing is
securely grounded via an 8-foot ground rod in the earth near the building.
In fact, there should be several such ground rods for a metal roof.

The average frequency of a lightning discharge is around 125 KHz, so you can
use that to calculate lightning rod cable lengths, etc.

You might do well to contact the other tenants in the building and see how
they feel about installing a proper lightning diversion system, including a
proper lightning rod and cable.

Happy New Year,
Dick







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