Water gets into an outdoor junction box through its cable entries, not through its walls. Seal an outdoor junction box by entering cables from the bottom through correctly sized and tightened glands, forming a drip loop below every entry, and giving the box a drain or breather at its low point. Keep any field-applied sealant as a second line of defense, not the only one. A box that passes a rainstorm but traps condensation fails just as surely a month later. The install has to handle water that arrives and water that forms.
Where the water actually gets in
Three paths account for almost every wet outdoor box. The first is a loose or oversized gland: the cable slides in the seal, or the gland body was never tightened against the entry hole. Water then runs straight down the jacket into the box. The second is capillary action along the conductors inside the cable, which pulls water past a marginal seal even when the outside looks dry. The third is condensation. A sealed box that swings through the dew point every night collects water on the ceiling, which drips onto the splices. The condensation guide covers that mechanism in depth.
Tape is not a gland. A spiral vinyl wrap relaxes with heat and leaves helical gaps, and it was never designed as the sole seal for a connection in driving rain. The sealing job belongs to the gland and the gasket; everything else is backup.
What you need
- Cable glands matched to the jacket outside diameter of every cable, with the correct thread form for the entry holes. Trade sizes and thread families are covered in the gland sizing and thread compatibility guide; the same logic applies at every NPT and metric size.
- A gasketed box with a hinged door and a removable panel. Our 304 stainless wall-mount enclosures run from 6 x 4 x 4 in up to 60 x 36 x 16 in (H x W x D) and are rated NEMA 4X / IP66 by the manufacturer; not UL listed.
- A drill and step bit if you are adding entries, plus a deburring tool.
- Silicone rubber or EPDM sealing washers for anything mounted against the wall.
- Self-fusing silicone tape or a resin splice kit for any joint that must live outside the box.
- Thread sealant compatible with the gland material, if the entries are threaded into plain holes.
The install, in order
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Pick the mounting face and the orientation. The box goes on the wall or pole with the door facing away from prevailing rain, and the cable entries go on the bottom. If the product's own entry arrangement is fixed, plan for bottom or low side entries before you drill anything.
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Mark and cut the entries. Hole size follows the gland, not the cable: a gland for a 0.31 in jacket on a 0.25 in cable will not seal on the wrong hole. For a stainless box, the cutting method that keeps the rating intact is in the stainless cutout guide. Deburr and clean every hole before a gland touches it.
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Fit the glands from the inside out. Slide the sealing ring and the compression nut onto the cable first, then pass the gland body through the hole from inside the box. Torque the body and then the compression nut; hand tight plus a quarter to half turn is the usual range. The seal visibly bites the jacket. If you can pull the cable through the gland with your hands, it is not done.
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Form a drip loop on every cable outside the box. The cable should drop below the level of the gland before it rises back up into it, so water running down the jacket drips off at the low point instead of following the cable to the entry. A 2 to 4 in (50 to 100 mm) drop is enough for most camera and control drops.
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Seal the box to the wall. A gasket or a continuous bead of neutral-cure silicone behind the mounting flange stops water that runs down the wall from wicking behind the box. Use neutral cure, not acetoxy: the acetic acid in cheap silicone attacks some metals and rubbers over time.
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Make the splices inside, not outside. Every connection lives inside the box with a service loop of cable. If an Ethernet joint must be made outside, use a properly glanded and gasketed arrangement rather than a tape wrap.
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Give the box a way to drain and to breathe. A small weep or drain at the lowest point of the box lets condensed water out. 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; check the edition your authority having jurisdiction enforces. A sealed small box can often live with just a low weep, a larger one wants a proper breather. The moisture side of that choice is covered in the condensation guide.
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Point any field-drilled weep downward and test it. With the cover off, pour a cup of water along the top of the door and check that nothing pools. With the cover on and the glands made up, run a garden hose at the box for a minute or two, then open it and look.
Checks when you are done
- Pull test every cable at its gland; nothing slides.
- Sight along the door gasket with the latch closed: even compression all around, no visible gap. How a gasket's material affects long-term compression is one of the outdoor sealing details in the outdoor enclosure guide.
- Every drip loop hangs below its gland.
- The weep or drain is open and points down.
- After the first heavy rain, open the box: dry floor, no droplets on the underside of the roof.
Mistakes that cost you the rating
A watertight box installed badly is a wet box. The usual failures:
- Top entries with no drip loop, so rain rides the cable straight in.
- A gland hole drilled oversized and plugged with silicone instead of made right; the bead bridges and cracks with temperature movement.
- Tape as the only seal on an outdoor joint.
- A weep hole drilled after painting or coating, leaving burrs and a ragged edge that holds water against the metal.
- A breather added at the top, where it doubles as an entry.
- Over-torquing a plastic gland until the body cracks, or under-torquing a metal one until the seal never bites.
If the site gets hosed down rather than rained on, the whole sealing plan needs to be drawn before the box is ordered. Hose-directed water is a Type 4 environment, and the rating differences are set out in the outdoor enclosure guide.
When to specify a bigger or better box
If the box keeps collecting water despite a correct install, the problem is usually volume and heat, not holes. A camera drop with a midspan, splices and a service loop wants more depth than it seems. An 8 x 6 x 4 in wall-mount box handles a simple drop, and the 10 x 8 x 6 in box leaves room for the extras. For a salt-air or washdown site, step up to 316L. Where the standard sizes do not fit the mounting or the entry layout, we build custom stainless enclosures from one piece with the cutouts you set, delivered in 10 business days from drawing approval. If the question is really about a sealed enclosure that fogs or weeps rather than an install mistake, the condensation guide takes it from the other end.
Questions
Can I just wrap outdoor connections with electrical tape?
No. Standard electrical tape is a stretchy vinyl that leaves spiral gaps as it relaxes with heat cycling, and water wicks along the conductors inside the wrap. For an exposed joint, use a self-fusing silicone tape stretched as it is wrapped, or a two-part resin splice kit, and keep the joint inside the box where possible.
Where should the cable enter an outdoor junction box?
From the bottom, or from below on a side entry, so water running down the cable meets the gland from underneath. Top entries fight gravity for the life of the installation. If a top entry is unavoidable, form a drip loop that drops below the gland before the cable rises into it, and use a gland rated for that orientation.
Do I need a drain hole if the box is fully sealed?
If any cable enters the box, you cannot make it perfectly sealed, and even a sealed box breathes with temperature swings. A small drain or weep opening at the low point lets condensed water escape instead of pooling on the connections. NEC 314.15 permits approved drainage openings of 3 mm (1/8 in) to 6 mm (1/4 in) in boxes listed for wet locations.
Which junction box should I order for a camera connection point?
A hinged stainless box with a gasketed door, sized with spare depth for the splices and the service loop, works well. The 8 x 6 x 4 in wall-mount box suits one camera drop; the 10 x 8 x 6 in box gives room for a midspan or extra splices. Both are rated NEMA 4X / IP66 by the manufacturer; not UL listed.
