[TowerTalk] Centre Insulator - fiberglass or Garolite rod

[Jim Lux]

At 06:32 AM 9/29/2005, donovanf at starpower.net wrote:
>Mark,
>
>I've used Garolite (a tradename for Type LE phenolic) on my
>antennas for 35 years and I've never had mechanical or
>electrical degradations of any kind.
>
>There are two types of Garolite rod: machined and formed
>
>Machined rod is cut from flat plate stock.  As a result, all of the
>grain is exposed to the weather.  Formed rod is wound as a rod,
>so the grain is nearly concentric (like the rings in a tree).  This
>would be an ideal choice where significant voltages could be
>developed across the insulator such as when it bridges a
>loading coil.


There's also pultruded forms.. the fibers run lengthwise.  You see this a 
lot in structural composites.

breakdown voltages are more a function of the surface treatment than the 
bulk properties.  Creeping discharges over the surface will go about 3 
times the distance of a free air discharge, and both are lower breakdown 
voltage than even crummy composites.
Figure, for conservatism, 1 inch per 10 kV.

Jim.