Re: [TowerTalk] ground systems... ferrous conduit

[Jim Lux <jimlux@earthlink.net>]

At 02:31 PM 2/2/2005, Jim Jarvis wrote:

> Jim, W6RMK provided a link to the FAA's lightning ground and
> surge protection standards.  They include a requirement that
> cables pass through a grounded 10' long ferrous conduit (pipe),
> before entering a structure.
>
> I recall reading that this serves as a choke for current
> flowing on those cables.

For that matter.. how would one calculate the L and R of such a choke?

Consider it as a single turn inductor?  What's mu for mild 
steel?  Resitivity is 0.13 vs 0.017 for copper.

I have numbers for mu(relative) anywhere from 181 to 254 to 77, depending 
on the flux, for cast iron, and numbers from 100-3300 for steel.

It also has a lot of hysteresis, which would probably be a big source of 
loss (good, in this case). Since it's a transient, maybe there's better 
ways to analyze it.  Something like the analysis done in magneforming, for 
instance.



>  As a result, I've routed all my
> runs through a section of iron pipe, for as long as I can
> remember.
>
> On the other hand...I ALSO recall reading comments on here
> poo poohing the idea.
>
> Comments from someone who really knows?
>
> N2EA
> jimjarvis@ieee.org


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