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Re: [TowerTalk] Ground wire

To: Gary Schafer <>
Subject: Re: [TowerTalk] Ground wire
From: Jim Lux <>
Date: Mon, 17 Sep 2007 14:16:59 -0700
List-post: <>
Gary Schafer wrote:
>> -----Original Message-----
>> From: [mailto:towertalk-
>>] On Behalf Of Jim Lux
>> Sent: Monday, September 17, 2007 3:44 PM
>> To: Jim Miller
>> Cc: TOWERTALK Reflector
>> Subject: Re: [TowerTalk] Ground wire
>> Jim Miller wrote:
>>> I usually do this, not asking it clearly.  It makes perfect sense to me
>> but
>>> I know what I am trying to find out.
>>> I can run enough of the 3 wire #8 cords to be as large or larger than
>>> whatever is recommended.  What I should have specified is that the wires
>> are
>>> insulated (romax style) and then the separate runs of course are
>> insulated
>>> from each other and then bundled and ALL the wires at each end tied
>> together
>>> as if they were ONE conductor.
>>> Now the question.  I was wondering if the wires being insulated
>> individually
>>> will cause some adverse effect (being caused by their capacitance or
>>> inductance to each other) on their capability to properly handle a
>>> ("normal") lightning strike verses using a single conductor of similar
>> size.
>> The inductance will be LESS than a single conductor of the same cross
>> sectional area.  What you're basically implementing is a version of the
>> "bundled" conductors you see on HV transmission lines, or, for that
>> matter a form of Litz wire.
> Jim,
> Won't the inductance be greater because of mutual inductance between the
> parallel wires?


Think of it this way.  Say you had 2 wires side by side.. it has some 
mutual L.  Separate the wires by some distance.. the mutual L is less, 
so the overall L is less.

The solid conductor is sort of the limiting case where the wires are 

You also pick up some benefit from the fact that the "surface area" is 
larger in the multi strand case, so the impact of skin effect is less.

Terman has a description of this, and the equations..

> Also Litz wire must be specially woven to be effective and then its benefits
> are only good at low frequencies.

Actually, it doesn't have to be woven.  It can be parallel strands on a 
non-conductive/non-magnetic core.  Woven or braided is just more 
convenient, because, usually, you're interested in the lowest inductance 
for a given overall diameter, and the braid pattern does just that.  A 
better statement would be that special winding/braiding techniques are 
needed to optimize the performance of Litz wire, but one can make your 
own Litz wire by just bundling enameled magnet wire.  It will be lower L 
and lower AC resistance than the same amount of copper as stranded or 
solid wire, but not as good as the real thing.

The benefits vs frequency vary depending on the number of strands, the 
packing density, etc.  At some point, it doesn't buy you anything over a 
solid tube.

I used to use what was essentially coax braid over a fiber core as a low 
inductance HV Pulse conductor.

> 73
> Gary  K4FMX


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