## all my nema 4 boxes are fiberglass or polycarbonate. Before they are
closed up, I hit them with the hair dryer, and cook the insides.
I also install a fair wack of silica gel ..aka desiccant, inside each
box..like a lot of it. Silica gel will absorb up to 40% of its weight in
moisture , water.
When they are opened up, like a year later, they are bone dry, including
everything on the inside. Another method is to generate some heat
inside the enclosure, like through a pair of metal finned resistors etc. The
2nd resistor is for redundancy. We used the above technique when I worked
for the local telco for 34 years.. including lubing the large diameter x .25
thick rubber O rings. The O rings were replaced every year..along with the
silica gel..
both on spec.... and typ in the fall, before the bad wx sets in.
## If installing variable capacitors inside an enclosure, I used ceramic
vac caps. If any type of relay is to be used, I use ceramic vac relays. I
have had too many issues
in the past when using air variables..and also any type of open frame relay,
including the types with the lock down plastic covers. The metal,
hermetically sealed mech relays
are fine, provided the mating socket connection is good.
## another school of thought is to use weep or drain holes, in which case
silica gel cant be used, since it will absorb outside moisture. Metal
enclosures are the most likely
to form condensation on the inside...even with weep holes installed, everything
inside has this tendency to corrode. These days, if I have to use a metal
enclosure, it gets sealed
up tight, heat inside, and plenty of silica gel.
## Then u still have the issues where any cables etc, have to go in or out of
the enclosure. Access to any enclosure is yet another issue, esp if an
enclosure is way out on the boom.
Jim VE7RF
From: dwkanepe@aol.com
Sent: Tuesday, August 14, 2018 9:54 AM
To: jim.thom@telus.net ; towertalk@contesting.com
Subject: Re: [TowerTalk] Fiberglass Enclosure
Keep in mind that, unless there is zero humidity the day you seal up the
box...the interior of the box will become a terrarium...experiencing
evaporation/condensation cycles with fluctuations in temperature. All interior
components should be protected against corrosion (unless breathers/drains are
installed).
If using non-metallic polycarbonate boxes, one should avoid using any anaerobic
thread locking compounds as contact with polycarbonate can lead to stress
cracks developing.
Don Kane
WB2BEZ
In a message dated 8/14/2018 12:29:25 PM Eastern Standard Time,
jim.thom@telus.net writes:
Date: Sun, 12 Aug 2018 23:05:44 +0000
From: Wayne Kline <w3ea@hotmail.com>
To: Chuck Dietz <w5prchuck@gmail.com>, Grant Saviers
<grants2@pacbell.net>
Cc: "N2TK, Tony" <tony.kaz@verizon.net>, "towertalk@contesting.com"
<towertalk@contesting.com>
Subject: Re: [TowerTalk] Fiberglass Enclosure
## nema 4 boxes are water proof. You can test that urself with a garden hose.
I use hoffman boxes with the rubber gasket. I also noticed that on the hammond
version, the rubber gasket is replaceable. Either way, I would suggest
applying a thin
layer of silicone dielectric grease on the rubber gasket, before tightening
things down. Then the
rubber gasket will last longer....and 100 % zero water, moisture ingress.
Jim VE7RF
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