RE: Ground box

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-uswest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi Ray,
         I can help explain this braidophobia very succinctly:

On 6 Apr 01, at 12:18, Tesla list wrote:

> Original poster: "Ray Robidoux by way of Terry Fritz
> <twftesla-at-uswest-dot-net>" <robidoux-at-basystems-dot-com>
> 
> Hi All,
> 
> I am very confused as to why this list has such a dislike
> for braid. I have seen many comments like this against the
> use of braid in TC work. My experience with braid is
> that for the same amount of copper (and 90+% optical
> coverage) the braid is an order of magnitude better than
> solid wire at conducting RF energy. The reason for this
> is exactly why we use refer tubing in the primary of a
> TC. It is the skin effect, the fact that the center of
> a conductor is useless in conducting RF currents. Therefore
> you want to increase surface area in the conductor to
> decrease current density. When using braid the most
> important feature to examine is the so called
> "optical coverage". This is the amount of light blocked by
> the strands of braided wire (strand density). Braid comes
> in all sorts of optical coverage(OC), from 10-% to 90+%. One
> can imagine that 20% OC braid is useless, and in fact is
> typically used in conjunction with aluminum foil to make it's
> shielding and conducting properties better. I would not use
> any braid with less than say 90% OC. If you look at the pics
> that Terry has shown, which is going to be the better conductor,
> I find it hard to believe its the center wire which has maybe
> 1/10th the amount surface area than the braid. I would like
> to hear others thoughts on this matter.
> 
> Ray

Unfortunately, it is precisely the skin effect that works against 
braid. There can be no doubt about how poor it is - I have measured 
it in a carefully crafted expt. I then went and proved the point by 
running a high current primary with a foot of it included. It got 
hotter than the brass blocks holding the gap electrodes.
      The strands duck and dive under each other along the length. 
Since skin effect is trying to keep current near the outer surface of 
the braid, the current has to hop from one strand to another at every 
point. Result: to RF, braid is like including thousands of 
connections in series, and contact connections are generally less 
than perfect. Braid was the standout worst performer in my tests by a 
country mile.

Malcolm