Re: [TowerTalk] Ground Radials Insulated or Not

[Jim Lux <jimlux@earthlink.net>]

At 07:00 PM 12/6/2004 -0500, Tom Rauch wrote:
> > But is a good RF radial grounding system really "one of
> the best lightning
> > grounds you can get".  A raft of small wires might well be
> a worse
> > lightning ground than a few nice big wires or rods.  The
> smaller wires may
> > fuse with the lightning current.  Say you get a 20kA
> strike and you've put
> > in 60 wires. That's 300+ amps into each wire (if the
> current divides
> > equally, which it probably won't). 300 Amps is a ballpark
> fusing current
> > for AWG10 wire in air (admittedly, that doesn't take into
> account the short
> > duration of the lightning impulse, etc.)
>
> Not that it means anything, but I've never seen a BC station
> radial wire melted or any of my own, despite years and years
> of strikes. I only use #16 radial wire, and often only 50-60
> radials. This includes my 318 ft tower.

Do you also have a ground rod(s) or Ufer ground at the tower base? Or, are 
you depending on just the radial field for lightning protection?



> I've always considered multiple radials to be a very good
> ground for lightning, and either that's correct or I've been
> very lucky for the 35 years I've had towers over 130 ft
> tall.
>
> I have lost the shields of cables where they run between
> large independent ground systems, mostly the shields of F6
> or F59 size cables that use aluminum foil shields. In one
> case the shield of 7/8th heliax where it ran between a tower
> and the radial system. I really think that was caused by a
> piece of old guy line lying on the coax and across the
> radial buss.  Never have had ground radials melt, or hard
> (not plumber's solder) silver soldered joints unsolder.

Could this be due to the rise in voltage at one end of the shield relative 
to the other?  Was it an overcurrent failure or an overvoltage failure 
(i.e. melted metal or blasted through insulation?)



> 73 Tom

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