Rain gets into an enclosure three ways: through an opening you cut, along a cable that bridges the gasket line, and out of the air itself as condensation. Make an electrical enclosure waterproof by closing the first two and managing the third: choose a rating for the water it will actually see, put every entry on the bottom through sized glands, drip loop each cable, and let trapped moisture leave instead of pooling. This article walks that workflow for a new design, in the order you should make the decisions.
Decide what waterproof has to mean
No enclosure is waterproof in the everyday sense; the word only means something against a test. Write the requirement as a rating, not an adjective. NEMA 250 and IEC 60529 are the two systems you will meet, and they are tested differently.
- NEMA 4: rain, sleet, snow, and hose-directed water from any direction. The usual choice for outdoor equipment and washdown areas.
- NEMA 4X: Type 4 plus corrosion resistance, so 304 or 316L stainless rather than painted steel.
- NEMA 6P: prolonged submersion. This is the submerged-meter case, and it is a different box, not a better gland.
- IP65 / IP66: dust-tight, and protected against jets of water. IP66 uses a stronger jet than IP65; the tests are laid out in IP65 vs IP66 water jet tests.
In US installations, an IP code is not a substitute for an enclosure type rating under NEC 110.28, so a spec that calls out Type 4X needs the NEMA number. Ratings are manufacturer ratings for the specified design; our enclosures are rated NEMA 4X / IP66 by the manufacturer, not UL listed. If your project or inspector requires a listed enclosure, that is a separate question about UL 50E evaluation.
For most outdoor, wall-mounted equipment that will never sit in water: Type 4X, or IP66 where the drawing follows IEC 60529.
Where the water gets in
A gasketed stainless box with an undamaged door gasket does not leak through its walls. Every leak traces back to an entry:
- A hole cut too large, or a gland torqued down on nothing.
- A cable running downhill into the gland, so water wicks along the jacket past the seal.
- An entry on the top surface, where gravity works against you all day.
- A conduit hub or knockout blank left unsealed.
The fix is a discipline about where and how cables cross the wall, not a better gasket. The fundamentals of cutting and sealing are in the cutouts, glands and HMI windows guide.
Put every entry on the bottom
Bottom entries put gravity on your side. Water running down the outside wall reaches the gland from above the seal, not through it. Plan the layout before you order, because the bottom plate is where the gland count lives:
- List every cable: power in, signals out, spare capacity for at least two more.
- Assign each cable a gland position on the bottom surface, spaced so gland bodies and nuts do not collide.
- Size each hole to the gland's specified drill size, not to the cable. An oversized hole gives the gland nothing to compress against, and the seal is gone. Thread types matter here too; if you are torn between NPT and metric hardware, [NPT vs metric cable glands](comparison is covered in our NPT vs metric article) is decided by the enclosure's tapped holes, not by the cable. For a common metric size, see G3/4 cable gland sizing and thread compatibility.
- Keep the lowest entry far enough from the inner wall and floor that the gland nut fits and the cable can bend.
If conduit rather than cable feeds the box, the entry logic is the same but the hardware differs; bottom conduit entry into a NEMA 4 floor-mounted enclosure covers the floor-mounted case, and wiring methods into a NEMA 4 enclosure helps you pick the raceway.
A plain rain-tight box with a handful of bottom entries is exactly what our 12 x 10 x 6 in (305 x 254 x 152 mm) 304 stainless wall-mount enclosure is built for; in coastal or chemical air, the same size comes in 316L as the 12 x 10 x 6 in 316L stainless wall-mount enclosure. Both are hinged, gasketed boxes with a removable mounting panel, and we cut the gland holes to your layout from one piece.
Gland and drip loop every cable
A cable gland seals by compressing a rubber ring onto the cable's outer jacket. Three rules make it hold:
- Match the gland's clamping range to the cable's actual jacket diameter, measured, not from the datasheet's nominal.
- Tighten the seal nut until the ring grips, then the body nut until the thread bottoms. Under-tightened glands weep; over-tightened ones split the ring.
- Use a gland with an integral seal rated for the same ingress level as the enclosure. The gland is now the weakest link in the wall, so it must meet the same number.
Then add the drip loop. On the outside of the box, below each gland, bend the cable down and back up so it enters the gland from underneath. Water running down the cable drips off the bottom of the loop instead of following the jacket into the seal. A loop 2 to 3 in (50 to 75 mm) deep is enough on most wall-mounted boxes. Where a side entry is unavoidable, the drip loop is not optional; it is the only thing keeping the water out. The full pattern, including drains, is in seal an outdoor junction box: glands, drip loops and drains.
If a plug-in connector must cross the wall instead, pick one whose ingress rating matches or exceeds the enclosure, mount it through a gasketed bulkhead fitting, and keep the drip loop on the fixed side. Whatever you choose, install it per the maker's instructions, because the rating only holds that way.
Let moisture out: airtight is the wrong goal
A perfectly sealed box still breathes. Heat of day pushes warm air out through the gasket; the cool of night pulls moist air in, and that moisture condenses on the inner walls as the temperature drops past the dew point. This is why a box that never leaks a drop of rain can still be wet inside, and why chasing an airtight design is the wrong target. The physics are in condensation in a sealed enclosure: why the rating can't stop it.
For an outdoor box, plan for it:
- Fit a breather vent, low on a side wall or on the bottom, so pressure equalizes and moist air leaves.
- Fit a drain, or specify a drain hole at the lowest point, so anything that does get in can leave. Small approved drains in wet-location boxes are a long-established practice.
- In humid or high-dew-point sites, add a small anti-condensation heater; sizing is in the enclosure condensation guide.
- Never combine a drain with a submersion requirement; a Type 6P design manages moisture differently.
Checks before you close the door
Run down this list at commissioning:
- Every entry is on the bottom or drip-looped; nothing enters through the top.
- Each gland's clamping range matches its cable jacket, and both nuts are tight.
- Unused holes carry sealed plugs, not tape.
- Door gasket seats evenly with no twist or pinch points.
- Breather and drain are open, oriented down, and not painted over.
- Inside surfaces are dry at handover; any fog means revisit the vent and heater plan.
Specify it on the order
The cheapest waterproofing is cut into the box before it is built. Order the enclosure with your gland pattern drawn: material and grade, outside size, and each hole's position and diameter, so the rating is never put at risk by a field drill. We build custom 304 and 316L stainless boxes that way, from one piece, delivered in 10 business days, counted from your order or, for custom work, from your approval of the drawing. Start from custom stainless enclosures or browse standard sizes in stainless wall-mount enclosures, and see how outdoor site conditions drive the choice in the outdoor electrical enclosures guide.
Questions
Can I drill my own cable entry holes and still keep the rating?
Yes, if you drill correctly sized holes for the glands you will use, deburr them, seal around the gland and follow the enclosure maker's rules. Any field modification sits outside the manufacturer's rating, so many buyers order the cutouts with the enclosure instead, from the drawing, at no risk to the seal.
What rating do I need for rain only, never submersion?
For rain and hose-directed water, NEMA 4 or 4X covers it; IEC 60529 IP65 or IP66 is the international equivalent. If the box can sit in standing water or be submerged, you need a Type 6P design, which is a different enclosure, not a better gland.
Are IP-rated connectors as good as glands?
A moulded connector rated IP67 keeps the rating when installed per its instructions, and it suits devices that disconnect in the field. For fixed wiring through a wall, a gland on the cable's outer jacket is simpler, cheaper and easier to inspect.
Why is my enclosure fogging inside even though it does not leak?
Sealed enclosures breathe with temperature swings: air leaves hot and pulls moist air in as it cools, so water condenses on the walls. That is condensation, not a leak. Manage it with a breather vent, a small heater and, where the design allows, a drain.
