Short answer: pick a bulkhead connector or cable gland whose datasheet states a rating, cut the panel hole to the printed size within about 0.04 in [1 mm], and let the elastomer ring under the flange do the sealing. Skip the sealant bead; it bridges a mis-drilled hole, hides it, and turns your next connector swap into a chisel job. On a stainless enclosure the wall blocks RF, so your antenna or network lead exits through this one penetration, and that penetration is worth installing properly. Here is the connector to pick, the hole to cut, six steps on the bench, and the checks that prove the seal before the box goes back on the wall.
What you need
- A bulkhead connector or gland with a stated rating: IP66 for rain and hose-down, IP67 for 1 m [3 ft] of water for 30 min, IP68 where the maker prints a depth and a time.
- The datasheet's panel hole size, with the gasket, O-ring, washers and rear nut supplied with it.
- A hole saw or step drill to that size, plus a deburring tool.
- Silicone grease for the rubber; dielectric grease belongs on threads only, since it insulates contact faces.
- A metal dust cap with a rubber O-ring, for any connector that spends time unmade-up.
- Silica gel desiccant, because sealing keeps liquid water out but not the humidity that rides in with service air.
Our 304 and 316L enclosures are rated NEMA 4X / IP66 by the manufacturer; they are not UL listed. Every connector you bolt through the wall carries its own maker's rating instead. For the fundamentals behind holes and glands, the cutouts, glands and HMI windows guide covers the ground this article builds on.
Pick the connector for the water it will meet
Match the rating to the duty, not to the biggest number on the shelf. Rain, spray and washdown are jet duty. Standing water is immersion, and IEC 60529 tests the two differently, so the codes are not interchangeable.
| Duty at the wall | Ask for | What the test does |
|---|---|---|
| Rain and hose-down | IP66 | powerful jets: 12.5 mm nozzle at 100 L/min, from 2.5 to 3 m, for at least 3 min |
| Brief submersion | IP67 | 1 m [3 ft] of water for 30 min |
| Continuous or deeper immersion | IP68 | the depth and time the maker states |
| Washdown with salt or chlorides | NEMA 4X stainless wall, 4X-rated hardware | hose duty plus 200 h of salt spray |
In US installations, NEC 110.28 states that IP ratings are not a substitute for enclosure type ratings. Name both on the drawing: an IP66-coded connector on a Type 4X wall satisfies a US spec and an international one at once. The weakest part sets the assembly. An IP54 USB feedthrough through an IP66 wall makes the assembly IP54, because the lower rating marks the path the test water takes.
The weatherproof SMA bulkhead checklist walks the four sealing surfaces inside the connector body, and what watertight and gas-tight gland ratings prove sorts the claims a test actually backs.
Cut the hole to the printed size
If the box is already wired and live, lock out and verify absence of voltage before the first chip is cut.
The hole size comes off the connector datasheet, and the tolerance is tighter than it looks. The gasket under a bulkhead flange is usually about 0.08 in [2 mm] wide, so the hole gets one grip width and little more.
Worked example: a PG11 nylon bulkhead gland for a small antenna lead. The datasheet fits 0.06-0.08 in [1.4-2.1 mm] cable, on a thread 0.73 in [18.6 mm] across, and calls for a 0.75 in [19 mm] panel hole. At the printed size the radial clearance is (19 - 18.6) / 2 = 0.2 mm per side, so the 2 mm gasket lip still overlaps metal by 1.8 mm. Drill 0.04 in [1 mm] oversize and the clearance grows to 0.7 mm per side, leaving 1.3 mm of lip on metal: more than a quarter of the grip gone for 0.04 in of slop. A hole drilled 0.5 mm off center adds its offset to one side, leaving about 0.8 mm of lip there. Stay within 0.04 in [1 mm] of the printed size and keep the drill square; those two habits are most of the seal.
An SMA bulkhead jack needs a smaller hole, typically 0.25 in [6.4 mm] as most datasheets print, and seals the same way: gasket outside, O-ring inside, rear nut behind. Deburr both faces, because a chip under the gasket stands the lip off the wall by its own thickness. Keep the gasket's footprint on flat metal, at least one flange width from any bend or weld seam, so the flange cannot rock.
For cutting technique on stainless (speed, feed, backing the wall), see how to cut a hole in a stainless steel enclosure. What drilling does to a rating explains why a factory-cut opening and a clean field hole are treated differently.
Fit the connector in six steps
- Deburr both edges of the hole and wipe the wall down; one chip under the gasket is a leak path the whole way round.
- Slide the outer gasket onto the connector body and seat it flat against the outside wall.
- Push the body through and add the inner O-ring against the inside wall; bulkhead hardware seals both walls, which is what keeps it tight from either side.
- Thread the rear nut on, tighten hand-firm, then about a quarter turn with a small wrench. The gasket should bulge evenly all round; a flat side means the flange is rocking.
- For a gland, pass the cable through the grommet and tighten the clamp until the rubber grips. Match the printed range: the PG11 example takes 0.06-0.08 in [1.4-2.1 mm], and a 0.12 in [3 mm] cable on it leaks along its own jacket. To pass a molded plug instead of bare cable, getting a connector through a cable gland covers the sizing.
- Wipe a little silicone grease on the threads, make the joint up, and fit the O-ring dust cap over anything left unconnected; the cap keeps threads clean and sheds rain between uses.
The gland version of this job, with grommet sizing and torque habits, is covered step by step in installing a cable gland without losing the rating.
Why the sealant stays in the drawer
Caulk and hot glue look like cheap insurance, and they are why a sealed-looking install still drips. A bead bridges an oversize hole, so the error ships inside the wall. During a hose test it traps water at its edge and holds it against the joint. It also bonds the connector to the panel, so your next service cracks the bead and starts the leak it was meant to stop.
The rated path needs no help: the rubber ring squeezed by the clamping nut is the seal, and it works dry. Sealant earns a place only on a repair, where a hole is already oversize and the honest fixes are a larger gland, a blanking plug or a patch plate. Sealing a wrongly drilled hole takes that job in order.
Checks before the box goes back on the wall
- Gasket view from outside: even bulge all round, no flat spot, and no gap you can slide a 0.002 in [0.05 mm] feeler under.
- Pour test: with the door closed, pour 1 L [about 1 qt] of water over the wall above the connector across 30 s, then open and look. A dry wall under the joint catches most fitting errors and costs a minute.
- Immersion claims get the maker's check: IP67 means 1 m for 30 min, so a sink run at bench depth proves your joint but not the rating. Test at the depth the spec names.
- Humidity: drop in a silica gel pack and regenerate it at about 120 C [248 F] for 2 h when the indicator changes. A vent is the wrong cure for trapped humidity; whether a breather vent keeps a NEMA 4X rating explains what a vent costs a sealed box.
Mistakes that cost the rating
- Hole past tolerance: beyond 0.04 in [1 mm] over the printed size the lip bridges air, and jets find it.
- Chips or a burr under the gasket, or a flange landed on a bend.
- Sealant standing in for the gasket.
- Gland grommet off range: the PG11 takes 0.06-0.08 in [1.4-2.1 mm]; a thicker cable passes the clamp and leaks down its jacket.
- A plastic push-on cap as the only seal on an exposed joint.
- The lowest-rated part: one under-rated feedthrough sets the whole wall's rating.
What to put on the order
The cheapest watertight penetration is the one the factory cuts. Send the connector datasheet with the hole size marked, plus the positions. The cutout designer lays holes, glands and display openings on any face, checks spacing, and exports the layout with your quote request. The custom stainless cutouts page compares a new opening in a catalog body with a fully custom one. Holes arrive deburred at the printed size, and the box is delivered in 10 business days, counted from drawing approval for custom work. For a connector you unplug every shift, pick the hardware before the layout; bulkhead cable gland vs one gland for removable outdoor cables makes that choice.
The decision, case by case
- Rain, spray and hose-down: IP66 or Type 4X hardware, printed-size hole, rubber ring and rear nut, dust cap on the unmade-up connector. This covers most outdoor wall-mount panels.
- Possible submersion: IP67 for a brief dunk, IP68 where the maker prints depth and time; test at the printed depth and size the gland to the cable within its range.
- Humidity with no liquid water: install the same way, then control moisture inside with silica gel instead of opening the rating with a vent or covering the joint with sealant.
Catalog dimensions to compare
Compare these catalog dimensions with your component layout. Open each enclosure for its rating, material and usable space, then check those specifications against your application.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 12 × 10 × 6 in | 304 stainless | 12 x 10 x 6 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 16 × 14 × 8 in | 304 stainless | 16 x 14 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
| 20 × 16 × 8 in | 304 stainless | 20 x 16 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can I seal a bulkhead connector with silicone instead of its gasket?
A bead hides the problem rather than solving it. The rated seal is the elastomer ring squeezed by the rear nut; at the printed hole size it overlaps metal by 1.8 mm [0.07 in], and sealant on top only traps water at its edge and makes the connector un-serviceable. Keep silicone grease for the threads of an outdoor joint, and fix an oversize hole with a larger gland, a blanking plug or a patch plate.
What hole does a PG11 bulkhead gland need?
Drill 19 to 19.5 mm [0.75 to 0.77 in] and stay within about 0.04 in [1 mm] of the printed size; a standard PG11 bulkhead gland is built around that 0.75 in [19 mm] panel hole. Deburr both faces so the gasket lip lands on clean metal, and keep the drill square. At the top of the tolerance the lip still keeps about 1.3 mm of overlap on metal instead of the 1.8 mm it holds at the printed size.
Can the antenna stay inside the enclosure?
In a plastic case, yes: RF passes through the wall. In a 304 or 316L stainless enclosure the metal shields RF, so the antenna leads out through the bulkhead connector. Cut its hole to the datasheet size and keep a silica gel pack inside, because humidity that rides in with service air condenses at night even on a wall that holds liquid water out.
Do dust caps keep an unused bulkhead connector waterproof?
A metal cap with a rubber O-ring, fitted finger-tight, protects the threads and sheds rain between uses; keep one on any connector that sits unmade-up outdoors. Treat it as splash protection rather than a rated penetration. The assembly's rating comes from the through-sealed connector, and a loose plastic cap leaves the threads open to driven spray.
