[TowerTalk] Scotchkote and Liquid Tape
John R Bookout K7JB
Wed, 04 Nov 1998 01:45:54 -0800
Your description of scotchkote made me think of perhaps another use. In
the 1970's, use of aluminum as electrical conductors in wiring homes and
buildings was practiced in the area where I live. Personally, I do not
know what the county inspectors were thinking when they allowed and
condoned this practice, because over time, aluminum oxidizes readily and
looses its ability to remain a good conductor, especially when cut and
joints are made. As a result, when aluminum conductors are joined by a
wire nut or some other mechanical connection, the joint soon develops an
electrical resistance, hence when current flows through the joint we see
IR drop and heat. This leads to electrical fires in these buildings
constructed with aluminum wire.
A contractor friend of mine and I got into this conversation the other
day and he believes that the integrity of an electrical connection can
be maintained over time if oxygen and water is kept away from the
joint. As I understand it, it is even possible to join aluminum and
copper in connectors labeled CU-ALR along with a special paste to keep
the joint from oxidizing. I have never seen nor used scotchkote, but
from your description I began to wonder if it would be yet another
product to use in making these kinds of connections. Any comments?
Kurt Andress wrote:
> To all connection Goopers,
> My apologies for sending off my last post without finishing it. Got distracted by
> the XYL, and clicked on the wrong button. Awh shucks!
> John (KF4MZD) offered some good comments about the 3M Cold-Shrink Wrap material.
> I have not used it and, therefore, cannot comment.
> I'm sure there is certainly more to consider on this subject, than has been
> recently presented.
> Back to finishing my comments about Scotchkote, and my experience with it.
> What makes the method I've been taught and suggested so effective is the seal
> that is obtained between the substrate (coax jacket and connector metal parts)
> and the tape overwrap. The Scotchkote has been designed to tenaciously bond to
> clean metal parts, coax jackets and the adhesive on the vinyl 3M tapes. Good or
> cheap PVC tapes don't work so well with Scotchkote. Yet, it seems to work fine
> for sealing non-contaminating jacketed PVC coax cables.
> The way water gets into the connection is along the primary interface (first
> layer of tape against the cable jacket, connectors, and tape). We can put
> hundreds of layers of tape and some kind of GOO on a connection, but the only one
> that really counts is the first layer!
> After that, the second most available path for moisture into the connection is
> between the wraps of the tape. But if all of them are wrinkle free and bonded to
> the connection substrates, there still is no path for the moisture migration.
> The UV deterioration problem with the Scotchkote goes away if we put it
> underneath the tape, where the UV can't get to it! The stuff brushed over the
> outside is just for giggles.
> Every time I have taken apart a connection that had the Scotchkote applied first,
> before the tape wrap, I have seen the tape adhesive & parts of the tape separate
> and remain bonded to the connection. This tells me that the Scothkote provides a
> better bond to the cable and connectors than the tape adhesive bonds to the tape!
> Sure, one has to slice the taped connection to get it apart, like a banana peel.
> That's because the tape is so strongly bonded to the connection that simple
> peeling of the wrapped tape is impossible. This strongly suggests that the
> primary seal against water migration on the first layer is pretty good!
> For those that really hate having some black stuff stuck to the outside of their
> connections, after 10 years, by all means use something else.
> What puzzles me the most about this is that 3M doesn't suggest this method of use
> on the can of Scotchkote.
> It took an old Motorola field service technician to show me how this stuff really
> works best.
> A 10 year old connection that has some black stuff on the outside and is shiny on
> the inside is pretty FB at my QTH!
> For connections that can't be suitably tape wrapped, the Liquid Tape is probably
> better because of its UV resistance, if it actually can bond to the metals of the
> This usually requres complete removal of the joint compound, from all exposed
> 73, Kurt
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