Short answer: yes — IP55 takes any rain a sky can drop on it, with roughly a thousand times margin. IEC 60529 earns the second digit 5 by firing water from a 6.3 mm nozzle at 12.5 L/min; a violent cloudburst puts about 0.013 L/min on a gate-pillar device. Snow is not jets either — it arrives as dust and leaves as melt water. Where IP55 lets you down is the hose, the pressure washer, and the joint where the box meets a wet wall, and those are mounting choices as much as rating choices.
What IP55 promises, digit by digit
Read IP55 as two separate promises. The first 5 is dust-protected: some fine dust enters, but only in amounts the equipment shrugs off, and full dust-tightness is the next digit up. The second 5 is water jets: IEC 60529 tests it with a 6.3 mm nozzle delivering 12.5 L/min, swept over every surface from about 2.5 to 3 m away for at least 3 minutes. Rain has to beat that, and it cannot.
The rating belongs to the enclosure as it left the test bench. Cut a hole and the assembly takes the rating of its weakest part, gland included — the same weakest-part rule that governs vents and drains. For the full ladder of codes, work through the IP rating chart; this article stays on the water half of IP55 and the weather it covers.
Rain against the second digit
The ladder is easier than it looks, because weather runs out halfway up it. Digit 3 is water sprayed at up to 60° off vertical — ordinary rain on an upright face. Digit 4 is splashing from any direction, which is wind-driven rain bouncing off ground and walls. By digit 5 you are already past weather and into a directed garden hose.
| Second digit | IEC 60529 test | What that means in weather | Where it fits |
|---|---|---|---|
| 3 | water sprayed up to 60° from vertical | rain on a sheltered or upright face | under a soffit, inside a lobby |
| 4 | splashing from any direction | driving rain, splash off the ground | open wall, fence post |
| 5 | jets, 6.3 mm nozzle, 12.5 L/min | all of the above plus a stray hose | gate pillar, facade |
| 6 | powerful jets, 12.5 mm nozzle, 100 L/min | hose on full, washdown rinse | washdown areas, farmyards |
| 7 | immersion, 1 m for 30 min | standing water, brief flooding | ground-level pits, flood-prone pads |
Digits 8 and 9 continue into continuous immersion and hot high-pressure jets; weather tops out at digit 7. Standing water is digit 7's job, so even an IP66 box stays out of puddles. Sheltered spots can stop at digit 4 — what IP54 really covers outdoors draws that line.
The downpour arithmetic: 100 mm/h on a 130 x 60 mm face
Take a compact pillar-mounted unit, the kind that sits at a pedestrian gate, with a 130 x 60 mm face catching the sky. Weather services class rain above 50 mm/h as violent, so size the storm at double that, 100 mm/h — gutter-overflowing thunderstorm weather. The test you are beating is the digit 5 jet: 12.5 L/min from a 6.3 mm nozzle, straight out of IEC 60529.
The rule is area times depth: the water a storm delivers equals the rainfall rate multiplied by the area catching it. Convert to litres per minute and set it against the test flow.
- Catch area: 0.130 m x 0.060 m = 0.0078 m²
- Depth per hour: 100 mm/h = 0.100 m/h
- Volume: 0.100 m/h x 0.0078 m² = 0.00078 m³/h = 0.78 L/h
- Per minute: 0.78 / 60 = 0.013 L/min
- Margin: 12.5 / 0.013 = about 960
The jet test hits your unit with roughly 960 times the water of the cloudburst, and with force behind every drop. Let the wind double the catch and let the storm double to 200 mm/h; the margin still clears 200 times. Decision: for rain alone, IP55 beats the weather by more than two orders of magnitude, so spend your effort on mounting and sealing instead. Cross to IP66 when a hose can reach the box, because digits above 4 buy hose resistance, not rain resistance.
Where IP55 actually fails outdoors
The rating answers water that falls or sprays on the box. Four other paths decide how an outdoor install survives its second winter.
Water running down the wall. A film streaming down a brick pillar carries almost no pressure, so the gasket already holds it; the mounting joint is the exposure. Hours of wetting wick into any gap left dry, and the wall keeps feeding water after the rain stops. Bed the back of the box on a compatible sealant, seal every fastener, and treat the joint like roof flashing; sealing a junction box to a brick wall against running water walks through the materials.
Snow, melt and freeze-thaw. Falling snow behaves like dust, and 10 cm of it holds about 1 cm of water, released over hours at low pressure — an easy day for the digit 5 gasket. The danger is the refreeze: melt water sits in a seam, expands about 9 % when it freezes, and pries the seam wider for the next storm. Put a hood over anything snow drifts against, lap seams downward, and where a panel must shed ice, sizing snow-melt heating for a wall is its own calculation.
Hoses and pressure washers. A hose on full is digit 6 territory — 100 L/min from a 12.5 mm nozzle — and a hot pressure washer sits up at digit 9. Farmyards, washdown bays and anywhere a cleaner works deserve IP66 from day one; IPX5 vs IPX6 for washdown sets out that choice.
Condensation, and the air already inside. Both digits say nothing about the air sealed in with the equipment. A box breathes through day-night temperature swings and fogs its own window at dawn, which makes condensation a heating-and-ventilation question — the outdoor enclosure guide covers sun, ice and the rest of the outdoor load.
The first digit deserves one outdoor look as well: pollen, road dust and most wind-borne grit sit comfortably inside dust-protected, and the dust digit's meaning for motor enclosures shows where you step up to dust-tight.
What to specify
In the US, the IP code works alongside a type rating, never in place of one. NEC 110.28 is explicit that an IP code cannot take the place of an enclosure type rating, and the practical answer is to write both: Type 3R for rain locations, Type 4X where hoses and corrosion reach, with the IP code alongside for international readers. Many manufacturers mark both for exactly that reason.
Know what each type does with the water. A Type 3R box survives rain partly by draining it — NEMA 250 and UL 50E let it carry 3 mm to 6 mm [1/8 to 1/4 in] openings at the bottom — and those open holes are why it stays a rain rating while a sealed box keeps hose spray out. That is the same weakest-part rule again: a drain or breather fitted to a sealed enclosure drops the assembly to that part's rating. NEMA 4X and IP66 side by side shows what the higher type buys you.
Every rating in this article is a manufacturer's rating, and ours are no exception: our stainless boxes are rated NEMA 4X / IP66 by the manufacturer and not UL listed, and NEMA itself writes the definitions and leaves testing to others. When you order, the stainless size finder runs from 6 x 4 x 4 in to 60 x 36 x 16 in, and the enclosure selector narrows it to your environment and inside space. Delivery is 10 business days anywhere in the world, counted from your order, or from your approval of the drawing for custom work. Send the cutout drawing with the order so the gland holes arrive factory-cut and the rating stays whole.
Enclosures for this job
Catalog sizes that suit the job this article answers, picked from its subject; open one for its full specifications.
| Enclosure | Material | Outside H x W x D / display | Rating |
|---|---|---|---|
| 16 × 12 × 8 in | 304 stainless | 16 x 12 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 |
| 24 × 20 × 8 in | 304 stainless | 24 x 20 x 8 in | Rated NEMA 4X / IP66 by the manufacturer; not UL listed |
Questions
Can I hose down an IP55 enclosure?
No. Hoses live at the next digit up: IPX6 is tested with a 12.5 mm nozzle at 100 L/min, and hot high-pressure washing sits at digit 9. The 12.5 L/min of the digit 5 test covers a stray, directed splash from a garden hose, so an accidental rinse is fine, but a regular washdown needs IP66 and glands rated to match.
Will snow damage an IP55 device?
Falling snow, no. It behaves like dust until it melts, and 10 cm of fresh snow holds about 1 cm of water, released over hours at next to no pressure. The damage route is melt water caught in a seam that refreezes overnight: water expands about 9 % when it freezes, so it pries the seam open for the next storm. A hood or a lapped, downward-facing seam solves it.
Does IP55 cover flooding or submersion?
No. Digit 5 is jets, and immersion starts at digit 7: 1 m of water for 30 minutes, with digit 8 covering continuous immersion on conditions agreed between maker and user. For a flood-prone pad, mount above the expected water line where you can and specify IPX7 or better where you cannot.
Is an IP rating enough for a US outdoor installation?
For the water, yes, but the code wants a type. NEC 110.28 says an IP code cannot take the place of an enclosure type rating, so a US outdoor spec names Type 3R or 4X and adds the IP code alongside for international readers. Remember these are manufacturer ratings, and ours are not UL listed.
Does the rating survive drilling a cable hole?
Only if the hole is sealed to the same level. The rating applies to the enclosure as tested, and the assembly settles at its weakest part: an IP68 gland in an IP66 box gives you IP66, while a cable through an open hole leaves the inside open to weather. Order the box with factory cutouts so each gland hole matches the box from day one.
