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Re: [TowerTalk] Weatherproof Sealant

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Subject: Re: [TowerTalk] Weatherproof Sealant
From: W0UN -- John Brosnahan <>
Date: Tue, 11 Jan 2005 10:17:23 -0600
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Professionals doing outdoor enclosures KNOW that you CAN'T seal a box.
You MUST let it breathe and drain.  Best to give it a good umbrella and
drain holes for condensation.

When I sold my company to Vaisala, OY, a large maker of environmental
sensing devices -- weather stations, radiosondes, etc -- they agreed that
they NEVER try to seal an outside enclosure.

Temperature changes cause it to breathe air in and out.  With time and more
temperature changes, the humidity condenses and never goes out unless
given a way to drain.  (Unless you do a full MIL-SPEC hermetically-sealed

73--John W0UN

At 09:17 AM 1/11/2005, Keith Dutson wrote:
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 is a specific
brand of silicone sealant recommended?  I understand the kind with vinegar
smell (acetic acid) will corrode electronics components in a sealed
environment.  Also, is there a need to insert a desiccant in the box?

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
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.

Thanks for any advice.

Keith NM5G


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