[TowerTalk] Fiberglass Enclosure

[Jim Thomson]

##  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 at aol.com 
Sent: Tuesday, August 14, 2018 9:54 AM
To: jim.thom at telus.net ; towertalk at 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 at telus.net writes: 

  Date: Sun, 12 Aug 2018 23:05:44 +0000
  From: Wayne Kline <w3ea at hotmail.com>
  To: Chuck Dietz <w5prchuck at gmail.com>, Grant Saviers
  <grants2 at pacbell.net>
  Cc: "N2TK, Tony" <tony.kaz at verizon.net>, "towertalk at contesting.com"
  <towertalk at 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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