Green crust on an RJ45 pass-through every few months, with light condensation on the enclosure wall, is a breathing problem, not a connector problem. The box is airtight enough to hold a partial vacuum but leaky enough to pull in humid air every night. When the enclosure cools after sundown, that air drops below its dew point and the water condenses on the coldest surfaces: the metal pass-throughs and the bottom of the door. Our enclosures are rated NEMA 4X / IP66 by the manufacturer; not UL listed, and the rating only holds when every penetration is made with rated hardware. This article walks the failure from symptoms to a permanent fix; for the dew-point math and heater sizing across a whole panel, see the condensation guide.
Symptoms and what each one points to
Each sign narrows the water path:
- Corrosion inside a pass-through or coupler, working fine for months then failing: water vapor condensing on the connector itself. The connector is the coldest, highest-metal-mass object on the wall of the box.
- Condensation film on the inside of the door and walls: the enclosure interior drops below the air's dew point. The air got there by breathing through a leak, usually a cable pass-through or an unsealed conduit entry.
- Water pooled or beading at the bottom only: liquid entry, not condensation. Look for a gasket flaw, a low-mounted hole, or a cable entering from above with a gap in the seal.
- Corrosion returns within weeks of cleaning and re-greasing the connector: the water source is active, and the grease is holding the water against the contacts.
- Staining or drip tracks below one penetration: that penetration is the leak. Follow the track to the hole.
The causes, most likely first
Breathing through the pass-through. A sealed box cycles in temperature every day. As it cools, the air inside contracts and draws outside air in through the weakest seal. RJ45 pass-throughs and cheap plastic glands leak by design at the cable exit and under the nut. Each cycle exchanges humid air for dry air, one way. Over months the box accumulates water, and the connector is where it condenses.
Grease that traps water. Anti-oxidant and dielectric compounds coat the contacts but do not exclude vapor. Water condenses under and behind the grease film, and the grease then holds it there. Grease is a corrosion inhibitor for properly sealed joints, not a sealant for a wet location.
Seals made with the wrong materials. Soft silicone smeared over a tightened nut, or tape that bonds to the cable jacket but not to the nut, cups water instead of shedding it. Mastic tape wrapped fully over nut and cable together works as a secondary seal; a bead of silicone on top of an unsealed joint does not.
Desiccant that saturated long ago. Silica packs absorb a fixed mass of water and then stop. They look the same saturated or dry. If they were the only moisture control, they finished the job quietly weeks after commissioning.
No pressure equalization at all. A perfectly sealed box still breathes through its gasket under daily thermal cycles, and it has no way to shed the water it traps.
How to check each one
- Open the enclosure in the morning, before the sun hits it. Note whether the door gasket shows water tracks or a uniform film inside. A uniform film points to condensation; tracks point to liquid entry at one spot.
- Inspect every penetration. Remove the connector or gland nut and look for water staining on the threads and inside the barrel. Staining there confirms breathing through that fitting.
- Pressurize the logic: close the door in warm afternoon air and check it after the next cold night. If condensation reappears with all cables sealed, the box is drawing air through the gasket or a mounting-foot hole.
- Weigh the desiccant if you have a scale sensitive to grams. Saturated silica gel is heavier than the dry figure on its datasheet. Compare, then decide whether it is a control or a symptom.
- Check the connector itself for a plated shell that wicks water along the cable jacket. A wet jacket inside a compression seal pumps water inward as it flexes in wind.
The fix, in order of what to do first
Eliminate the pass-through. The most reliable repair is to not have a field-terminated connector in the wet path. Run the cable through a proper cable gland and terminate inside the enclosure, on the equipment or a jack mounted on the mounting panel. Sizing glands for RJ45 plugs and their overmolds is covered in the RJ45 gland sizing article.
Make every penetration a rated one. Use a stainless cable gland with a sealing insert matched to the cable diameter, torqued to its spec, with a locknut and seal washer on the inside. Mastic tape over the installed nut and cable, wrapped so it bonds to both, adds a secondary seal that survives weathering.
Give the box a way to breathe and drain. Fit a rated breather drain at the lowest point. It equalizes pressure through a hydrophobic membrane, so the box stops sucking humid air past seals, and any trapped water drains out while spray stays out. A breather and a drain serve different halves of this job; the trade-offs are worth reading in the breather vent vs drain comparison alongside planning the whole water barrier.
Keep the interior above dew point. A small enclosure heater, thermostatically controlled, holds the inside air a few degrees above the dew point of the trapped air. This is the standard fix for boxes that must stay fully sealed; the dew-point arithmetic and heater sizing steps are in the condensation guide.
Dry the box before you close it. Replace saturated desiccant, or use fresh packs only as commissioning insurance, not as the permanent control. A humidity sensor inside a sealed enclosure tells you whether the fix worked before corrosion does.
What a shroud does and does not do
A sun-and-rain shroud reduces the temperature swing that drives breathing, and it keeps hose spray and direct rain off the fittings. That is worth having, and it slows the water input. But a shrouded box that still breathes still accumulates moisture, just more slowly. Treat the shroud as the last layer, added after the glands, breather drain and heater are right.
Stopping it coming back
- Terminate cables inside the enclosure on glands, never on unsealed pass-throughs in the weather.
- Keep desiccant out of the design as the primary control; use a heater where the enclosure must stay sealed.
- Mount glands on the bottom or lower sides where possible, so any water that gets past a seal runs out, not in.
- Specify a sloped or drained bottom for hose-down locations.
- Check gasket seating and latch compression at every service visit; a distorted door gasket is a breathing path too. If a battery shelf has bent the door flat, see enclosure battery shelf support without door distortion.
When to re-specify the enclosure
Re-specify when the fixes above cannot be retrofitted: no room for a heater, no low point for a drain, mounting feet blocking the gland positions you need, or the box itself corroding. A 304 stainless wall-mount enclosure such as the 6 x 6 x 4 in box or the 8 x 8 x 4 in box handles most outdoor sites; near coastlines or where de-icing salt and cleaners land on the box, choose 316L, like the 6 x 6 x 4 in 316L box. All of them are rated NEMA 4X / IP66 by the manufacturer; not UL listed.
When you re-order, put every cutout on the drawing so the glands land where you want them, low and staggered, with a breather drain at the true bottom. The cutouts and glands guide lists what a fabrication shop needs, and our custom enclosure spec guide walks the drawing. Custom enclosures are delivered in 10 business days, counted from your approval of the drawing. Browse the wall-mount stainless line to start from a size, or 304 stainless enclosures for the grade.
One design note on measurement: if you want proof the fix holds, log relative humidity inside the box for a few weeks. A properly drained, heated enclosure stays well below saturation through the night cycle; a breathing one tracks the outside dew point closely. A deeper treatment of dew-point control in industrial drying appears in a desiccant air drying dew point selection guide, which is useful when you must hold a box dry without a heater.
Enclosures in this article
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 6 × 6 × 4 in | 304 stainless | 6 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 8 × 8 × 4 in | 304 stainless | 8 x 8 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 10 × 8 × 6 in | 304 stainless | 10 x 8 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 6 × 6 × 4 in | 316L stainless | 6 x 6 x 4 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Will a shroud over the enclosure stop condensation?
It helps but rarely fixes it alone. A shroud cuts direct rain, sun load and the day-night swing of the box temperature, so less humid air is breathed in and less water condenses out. But as long as the enclosure breathes humid air through a leak path and has no way to shed that water, corrosion continues. Pair the shroud with sealed glands, a breather drain and dry air inside.
Why does anti-oxidant grease not protect the connector?
Grease only protects metal it fully coats in a continuous film. A pass-through that breathes pulls water vapor in behind the grease, and the grease then traps condensate against the contacts. It can make corrosion worse by holding water in place. Grease belongs on the gland seal and threads, not as the only barrier on contact surfaces.
Do desiccant packs solve enclosure moisture?
They buy time, not a solution. Silica gel absorbs a limited mass of water, then saturates and stops working while looking unchanged. In a small box with a real breathing leak, a few grams can saturate in weeks. Use desiccant for dry commissioning of a properly sealed enclosure, and replace it on a schedule, or replace it with a thermostatically controlled heater.
Can I just drill a weep hole in the bottom of the enclosure?
A hole changes the rating, so treat it carefully. A NEMA 4X-type enclosure is rated for hose-down and splashing water, and an open hole defeats that. The legitimate version is a breather drain: a gasketed, rated device that equalizes pressure and lets liquid water out while keeping spray out. If you only need drainage in a sheltered spot, NEC 314.15 permits approved drainage openings of 3 mm (1/8 in) to 6 mm (1/4 in) in boxes listed for damp or wet locations.
How do I stop the connector itself from corroding again?
Eliminate the pass-through if you can: run the cable through a gland and terminate inside the box on a jack or directly on the equipment, so no plated contact sits in the wettest spot. If you must keep a pass-through, seal it with a rated gland and mastic over the nut and cable as a secondary seal, keep the box interior above dew point with a heater, and add a breather drain at the lowest point.
