FWIW, Dow Corning makes 748 Non-corrosive RTV sealant (White). 100% Silicone
Rubber; Safe for food contact; Non-corrosive; Less objectionable odor; -67F to
+350F (-55C to 177C).
Applications: Sealing corrosive-sensitive electrical and electronic equipment
(electrical connections, wire entries, power and control cable connections,
etc.); Bonding and sealing food processing equipments; Formed in-place gaskets
for sensitive substrates.
I have the 3 U.S. Fluid Ounce ( 90 mL) tubes.
In general, NEMA-3R and 4X are the types of boxes you ought to use. However,
the 3R may only retain its "rain-tight" rating when it is "upright". There's
also no guarantee in a hurricane with horizontal wind driven rain, hi.
My personal rule, which I carry on to work whenever possible, is to never
penetrate the roof (top of the box) unless it's the last resort. Walls can be
penetrated with appropriate weather-tight connectors but even better if they're
under an eave of a roof (or lip of a box - that's how the 3R boxes are when
they are "upright"). Best to go from below whenever possible. It is also very
true that it is difficult to make a box watertight and dry (except for
specialized underwater boxes) especially here in the tropics (and as soon as
you start making holes in it). Don't even try. Use drain holes. When mounting
operating radio equipment (repeaters) permanently outdoors (at least here in
Hawaii) I put the entire equipment cabinet in a larger wall mounted cabinet (3R
or 4X) and use forced air ventilation to keep a stream of outdoor air
circulating through to keep moisture build-up to a minimum. Of course, filters
and deflectors are used. Compensation for your varied climate conditions must
also be taken into account. We're lucky in that regard.
If you must mount things internally and through a wall, consider putting a
little RTV on the screw before you drive it through the hole.
If you can find (and afford) specialized boxes some come with studs welded to
the back of the box and have a floating plate / chassis that sits on these
studs. This will allow you to mount some hardware without any holes in the
outer box (not counting ingress and egress of cables, etc.) These are common on
naval (brass) shipboard boxes but are very expensive. There are commercial
boxes as well. Unfortunately, electrical boxes with any special qualities are
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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