[TowerTalk] Non-corrosive RTV ; NEMA boxes

[Kimo Chun]

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 expensive.

Good luck.

Kimo KH7U