>Guys,
Are ther no gals on Tower Talk :-)?
(snip..)
> Although the box is watertight, there were water droplets between several
sections.
(snip...)
This raises an interesting question about mounting water-sensitive
components outdoors. Is it sufficient that the box be watertight, or must it
be airtight as well?
I have five boxes mounted next to my tower:
One is a large Greybar metal utility box specifically designed for outdoor
electrical terminations. The hinged door is lined with a rubber gasket and
is screwed down tight with clamps when closed. As delivered, there were no
other holes in the box. I drilled holes in the bottom for three PVC conduit
terminations as well as entry points for several coax, control cable and
ground runs (it's a *big* box - 20"x20"x8".) I used feedthrough bushings
with rubber inserts where possible, but did not seal around the bushings
themselves. The rubber inserts do not mate perfectly with some of the
control cables, but if there are openings they are very small. I sealed any
visible openings with silicone. I've opened the box a few times in the
winter, and have never seen a single drop of moisture inside. Everthing is
always bone dry in there. I often wonder if I should minimize opening that
box to keep moist air out.
I also have a standard outdoor AC breaker box. This box is not airtight, but
it is watertight. There are drain holes drilled in the bottom and a double
cover system with no gasket. (one metal cover slips over the brakers and the
hinged door closes loosely over that.) A conduit run enters the bottom and
two AC lines leave the sides. The bushings on the latter are well sealed.
One line runs to a stadard outdoor AC outlet box with a hinged gasketed
cover (the fit is not super tight.) I've never inspected the inside of these
boxes in the winter, but I've also never had any problems with the power. I
suspect that there is no significant moisture formation, or that if it is
forming there is no way it can short anything.
There is a large metal utility box on the tower that houses the relays for
my motorized crankup. This box is not water tight, but all cable entry and
exit is through the bottom and the door fits under metal overlaps so water
can't get in. The box has drain holes drilled in the bottom. So far, no
problems with the open frame relays in this box, although I've not looked
inside during the winter yet.
Finally, I have an Ameritron RCV-8 coax switch. It has no openings to the
outside and there is a silicone bead between the cover and housing. The
manufacturer specifically warns against drilling drain holes. The box is
certainly watertight, but I think some small amount of air could enter where
the control lead goes into it. No problems with the open frame relays on
this one after more than ten years of use.
If I can stand the windchill this week, I'm going to replace the Ameritron
with a set of 8 Topten switches for two-radio operation (six 1-of-2 and two
1-of-6.) The Topten switches are not sealed and not waterproof. I considered
building a separate box for them, but I found room for them inside the
Greybar box. The relays used by Topten are sealed.
My question is, what has been the experience out there with condensation
inside boxes that are watertight but not airtight? Has anyone seen evidence
of condensation inside boxes like that, and if so, do drainholes help or
make it worse?
73, Dick, WC1M
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