[TowerTalk] Liquid Electrical Tape?

[Jeff DePolo]

> I have heard the best is 3M Scotchkote.  However, I recently 
> inspected a
> coax connection on the outdoor 2 meter cable running from repeater to
> antenna (on top of 500 foot building).  It had been slathered with
> Scotchkote after sealing with two wraps of 88, one wrap of 
> 2228 fusion tape
> and two final wraps of 88.  It appears the Scotchkote was 
> useless in the
> harsh outdoor environment at 500 feet.  
 ... 
> 73 Keith NM5G

Scotchkote was never meant to be used as a "final coat", which,
unfortunately, is how it is most-often misused.  It is supposed to be used
between alternating layers of electrical tape (Scotch 33+, Scotch 88).  It
has no UV resistance, and as you saw, it just dries up, cracks, and becomes
useless if used as an outer coating.  Scotchkote is also a big ugly mess to
deal with up on a tower, especially if the wind is blowing; you may end up
with more of it on you than on the connection.

Unless there is a real good reason to do otherwise, we stick with the tried
and true "tape and taffy" method, starting with a "courtesy wrap" of regular
electrical tape, then mastic tape (aka butyl) squeezed and massaged to make
sure that there are no air voids, and forming it to yield a smooth contour
over the connection and tapering down to the cable diameter, and then three
wraps of electrical tape (regular 3/4" Scotch 88 for small cables, 1-1/2" or
2" Scotch 88 for larger diameters), one winding up, one back down, and one
back up again.  You don't want to use a big wad of mastic, just enough to
cover the connection and smooth out any irregularities.  If you use too
much, or if you make the final vinyl tape wraps too tight, the constrictive
force of the electrical tape wraps will cause the mastic to ooze out on hot
summer days.

The alternative that I prefer, but most tower crews don't have the patience
for, is using multiple layers of splicing tape (Scotch 130C, Scotch 23,
Plymouth "Plyvolt", etc.) instead of mastic.  Still use a courtesy wrap
first, and finish with three layers of 88 for UV protection.  The splicing
tape has to be stretched as it is applied in order for it to properly bond
to itself.

For things like omni antennas where the connector is recessed up into the
bottom of the mounting pipe, or yagis where the connector is very close to
the boom or other structural element, it can be damn near impossible to use
tapes to seal the connection.  High-grade thick-wall adhesive-lined heat
shrink is the best alternative, with Canusa being the preferred brand.
Canusa CFTV series is pretty much the de facto standard in the cable TV
industry for outdoor weatherproofing, and that's what we use.  Canusa heat
shrink is designed to be shrunk using a propane torch, so installing it on a
tower even with wind blowing at moderate speeds isn't a problem.

We've also been using "Rayvolve" spice covers from Raychem/TE for fiber
connections and the like.  We haven't been using them long enough for me to
form a definitive opinion of them yet.

Despite the advertising campaigns in recent years, silicone-based tapes like
"rescue tape" aren't anything new.  Personally I haven't found a reason to
use it for weatherproofing coax connections given the other existing
alternatives.  YMMV.

				--- Jeff WN3A



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