[1000mp] Braid or strap for ground wire...big question.

[Robert Shohet]

Hi Tom,

Thanks for taking the time and effort to post such an informative and
helpful explanation!

73

Bob KQ2M


> Calculating inductance is a task beyond my time and capabilities, but
> from experience I observe little difference in the inductance of a
> braided or stranded conductor and a smooth conductor.
>
> There is, however, and easily observed difference in resistance
> between the two.
>
> For example, in tank circuits a thick braided conductor removed from
> RG-8 coax has about the same current handling capability as a small
> number 16 or 18 solid wire. The looser or dirtier the braid, the
> worse the braid behaves.
>
> The type of lay also has a large effect. Densely woven or twisted
> braids or stands, especially those with fine stands, have much more
> heating and loss for a given conductor size.
>
> The primary loss mechanism in coaxial cable that has been internally
> exposed to moisture is corrosion or tarnish on the braid. As a matter
> of fact if the cable has a smooth solid shield and center it remains
> nearly as good when tarnished as when shiny!
>
> The reason for all of this is skin effect, which tries to confine the
> current to the surface of the conductor. If the surface has weaves
> that cause each conductor to periodically move to the center of the
> wire bundle, current tries to flow across the pressure connections
> between each of the small conductors. If those connections are not
> firmly pressed together, and if they are not clean and shiny with low
> resistance, the surface of the wire behaves like thousands of high
> resistance joints.
>
> The more radical the weave and finer the strand, the worse the
> problem becomes.
>
> Wires with gentle twists only have slightly more RF resistance than
> bare solid conductors, even when dirty. Woven conductors, unless
> physically clean and compacted together tightly, can have incredible
> resistance to high frequency current.
>
> Lightning is not dc, and does not behave like dc. It has significant
> energy content at high frequencies, and the energy peaks in the VLF
> and LF range. That's why braided and densely woven conductors are so
> poor for RF and lightning.