[TowerTalk] Weatherproof Sealant

[K8RI on Tower Talk]

Where is it going to be located?  Below ground? Above ground? on top of the 
tower?


>I need to weatherproof a relay box.  Under test conditions it accumulated 
>an
> inch of water in the bottom over a six month period.

What were the test conditions?

>  What is a specific
> brand of silicone sealant recommended?  I understand the kind with vinegar
> smell (acetic acid) will corrode electronics components in a sealed

It depends:  In a small, sealed area with the sealant in contact with the 
components the answer is yes, but using it to seal the edges of a box should 
not be a problem.

> environment.  Also, is there a need to insert a desiccant in the box?
Not normally.

In another life I worked in the chemical industry. We had to seal conduit 
and boxes to prevent gases and liquids from migrating through.  This was 
very rugged equipment and it was not at all unusual to find condensation in 
conduit.

>

I can't think of a reason to seal any boxes that aren't under water, or 
underground in the real world.  They need to breathe to prevent moisture 
accumulation, BUT in some conditions a vented box will cause water to 
condense on the relays. OTOH A sealed box can even force water into the 
cables through the connectors.

Typically, I try to use a box that is taller than the width which leaves a 
fair amount of space below the works.
Even a metal screen lower in the box will cause moisture to condense out, 
leaving the upper portion dryer.

I have one of the remote antenna switches mounted around 80 to 90 feet up on 
the tower.  After a couple of years it shows no sign of condensation inside. 
OTOH the connectors on the outside (bottom) are looking pretty weather 
beaten.  I'd say there has been a lot of corona up there.

> The box is NEMA industrial type, made of plastic with neoprene o-ring seal
> on lid.  However, there are many holes drilled for stainless hardware used

Mount the box upside down with the "dish" shaped part serving as a cover. 
Holes should be nowhre other than in the bottom.  Sealing holes in sides and 
tops is a losing cause.

> to mount the relay and connect wires to the exterior.  The relay itself is
> the open contact variety with self-cleaning contacts (hot switch 20 watts
> RF), and supposedly impervious to damp conditions.
>

Put a plastic pail over it of a dark color.

I'm serious.

http://www.rogerhalstead.com/ham_files/cablebox.htm
I use a Hoffman box (TM) about 3 to 4 feet above ground at the bottom of the 
tower.  The inlet (at the bottom) which is a foot long PVC  conduit stub, 
where all the cables enter is sealed with the soft, expandable white 
building foam.  The outlett (conduit to the basement) is not sealed. It is 
sealed in the basement.   Even though the box is steel I've never seen any 
condensation inside.  BTW, I should replace the photo of the box and cables 
as they have been rerouted are are much neater now.

Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com
> Thanks for any advice.
>
> Keith NM5G
>
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