A camera junction box with a broken back knockout cannot be made watertight again with the factory plug, putty or caulk alone. The dependable answer is a compression cable gland on the entry, or a properly rated enclosure whose wall you seal with a gland and whose gasket does the rest. This article covers the back-entry case for a box mounted under a soffit or on a wall, cable arriving from the attic or crawl space without conduit.
Why the factory back entry stops being watertight
Most camera junction boxes ship with the rear knockout closed by a thin felt or rubber backing. That backing seals a solid wall, not a wall with a cable through it. The moment you push an Ethernet cable through, you have a round cable against a rough hole, a gap that capillary action and wind-driven moisture will find, and no compression anywhere.
The camera-side entry is different: the camera necks into a designed grommet that compresses when the camera seats. The back entry has no equivalent, so it is the weak point. Sealing connectors inside the box, as the guide on sealing connectors inside an outdoor junction box covers, protects the splice; it does not stop water entering and sitting in the box.
Choose the entry method before you mount the box
Decide between three approaches before the box goes on the ceiling or wall, because two of them are hard to retrofit:
- Compression gland through the back wall. Drill the knockout to the gland's panel-cutout size, fit a nylon or metal gland rated IP68 at the gland, and tighten until the seal grips the jacket. This is the primary recommendation for a cable arriving without conduit.
- No back entry at all. Mount the enclosure flat against the soffit with the cable passing through a sealed gap behind it, and make the enclosure-to-surface joint the water barrier. This only works if the mounting surface is continuous and you bed the joint properly, as described in the guide on the thin outdoor enclosure sealing plan.
- Gland on a cable exiting through the wall of a bigger box. If the camera maker's box is too small for the RJ45 plus a service loop, replace it with a stainless wall-mount box and gland the wall once.
Duct seal packed around the cable is the common field answer. It is reworkable and stays pliable in cold weather, so it beats caulk for a temporary repair, but it is a paste joint with no mechanical grip. Sun cycles and dust degrade it. Use it only behind a gland, not instead of one.
Fitting a gland to the back entry
- Measure the cable jacket. A gland seals on the outer jacket, not the conductors. For Cat5e or Cat6 outdoors-rated cable, the jacket is typically 0.20 to 0.30 in (5 to 7.5 mm); match the gland's clamping range to your measured size. If a factory-molded RJ45 has to pass through, the gland cannot seal it, so terminate after the box or use a purpose-sized entry, covered in the guide on cable gland sizing for an RJ45 connector.
- Open the knockout to the gland's cutout size. For a common M16-style gland the panel hole is around 5/8 in (16 mm); for a 1/2 in NPT gland around 7/8 in (22 mm). Deburr the hole so the gasket seats flat.
- Fit the gland with its gasket on the outside face. The flat gasket under the gland nut must bear on the box wall, and the wall must be flat and clean. Remove loose paint and mill scale from contact surfaces.
- Slide the gland parts onto the cable in the right order. Cap, sealing insert or clamp, gasket, body. Reversing the order is the most common reason a gland leaks.
- Tighten the body nut and then the cap nut to hand-tight plus a firm quarter turn. The seal should visibly grip the jacket. Pull-test the cable gently; the jacket must not slide.
- Keep a drip loop below the entry. Water running down the cable should reach the low point of the loop and drop off, not wick into the gland. Glands, drip loops and drains are covered step by step in the guide on sealing an outdoor junction box.
Sealing the box to the mounting surface
The back entry is one barrier; the mounting joint is the other. On a soffit, the joint between the box flange and the ceiling is where wind-driven rain from a wet wall or a roof edge will try to get in.
- Bed the flange in a continuous bead of exterior-grade sealant, or fit a closed-cell gasket, and screw the box down evenly so the bead compresses all round.
- Do not rely on screws alone: fastener holes are entries in their own right, which the guide on mounting screws through an outdoor enclosure without leaks addresses.
- If the box has an open bottom cap, do not count on capillary action to hold water out of it; seal or gland that face too.
What to do about condensation, and why drain holes are not the answer
Even a well-glanded box breathes with temperature swings and will see some condensation. A drain hole smaller than about 1/4 in (6 mm) generally will not drain, because surface tension holds the droplet against the lack of internal pressure. At 1/4 in the hole admits insects freely. Condensation is better attacked by design: minimise trapped humid air, use a box with some internal volume, and manage the moisture path as the guide on condensation in a sealed enclosure explains. Dielectric grease in the female RJ45 cavity keeps a damp connector working even if a film of moisture forms.
When to replace the camera maker's box with a real enclosure
The camera junction boxes are small, and many jobs run out of room as soon as you add a service loop, an inline coupler or a small media converter. If that is your job, a gasketed stainless box is the cleaner answer: order it with the gland holes cut where you want them and mount it like any wall box.
We build 304 and 316L stainless wall-mount enclosures with a hinged gasketed door and a removable panel, manufacturer-rated NEMA 4X / IP66; not UL listed. The 6 x 4 x 4 in NEMA 4X wall-mount enclosure suits a camera pigtail with a short service loop, and the 8 x 6 x 4 in NEMA 4X wall-mount enclosure leaves room for an inline coupler. Both can be ordered in 316L for coastal or washdown exposure. Every opening is cut to your drawing, so the back entry arrives as a finished gland hole instead of a knockout you have to fight. Orders are delivered in 10 business days, counted from your order or, for custom work, from your approval of the drawing.
Checks before you close it up
- Pull-test each cable: the gland grips, the jacket does not slide.
- Shake test with the box dry: no rattle means the gland parts are assembled in order.
- Inspect the mounting bead all round; no gaps where the flange meets the soffit.
- Drip loop formed below every entry, nothing spanning tight.
- Connector grease applied and the door gasket seated before the final latch.
Mistakes that cost you the seal
- Reusing the felt backing as a seal. It never re-seals around a cable.
- Sealing a molded RJ45 through a gland. The gland clamps the jacket; a connector will not compress.
- A drain hole as the plan. It either will not drain or it feeds insects.
- Silicone over a dirty or dusty surface. Adhesion fails within a season.
- Skipping the drip loop because the cable goes up into a dry attic. Wet walls and roof edges still run water down the cable.
Questions
Can I just pack duct seal around the cable in the back hole?
It works for a season and it is easy to rework, but duct seal is a temporary joint. Sun-cycled putty and sealants creep, pick up dust and lose adhesion, and the factory felt plug behind the knockout never re-seals once broken. A compression gland costs little and holds the seal mechanically, so use duct seal only as a short-term fix or a second line of defense behind a gland.
Is drilling a drain hole in the bottom cap a good backup?
A drain hole below roughly 1/4 in (6 mm) usually cannot drain at all, because water surface tension and the lack of pressure inside the box hold the droplet in place. At 1/4 in the hole admits insects and dust freely. Either size an approved drain opening properly or leave the box sealed and design the entry so water never gets in.
Do I still need to protect the RJ45 connection inside the box?
Yes. The gland keeps bulk water out, but humidity cycles and condensation still reach the interior. Fill the female connector cavity with dielectric grease, and for exposed runs wrap the plug with self-fusing silicone tape. The gland is the primary barrier; treat the connector as the secondary one.
When should I use a proper enclosure instead of the camera maker's box?
When you need room for a service loop, an inline coupler or a small media converter, or when the factory knockout arrangement fights your entry direction. A stainless wall-mount box with a gland sized to the cable, available from 6 x 4 x 4 in (H x W x D) up, gives you space, a real gasket and a repeatable seal instead of putty.
