Short answer: an IP66 or IP67 mark tells you how a new box handled one water test — powerful jets or 1 m of immersion for 30 min. It tells you nothing about sun, cold, gasket aging or the nightly breathing that actually fills outdoor enclosures with water. Order by the datasheet's environment statement, the line that names a temperature range and states outdoor use in words, and treat the ingress code as one item on the checklist. A sealed box still breathes: a 10 °C night drop pulls about 3-4 % of its air through the gasket path, and the moisture in that air lands on your window as fog. The same rule covers our own boxes: our 304 and 316L stainless enclosures are rated NEMA 4X / IP66 by the manufacturer; not UL listed, and they still need the breather, heater and mounting decisions set out below.
Can a unit be IP66 and IP67 yet not rated for outdoors?
Yes — the ingress code and the outdoor statement come from two different places, and one datasheet can carry IP66, IP67 and even a partial Type 4X claim while its mounting line says the unit is meant for inside vehicles and rolling stock.
A rating measures the ingress path on a fresh assembly. Outdoor suitability is a claim about duty: sun, cold, icing, years of cycling, and who owns the condensation problem. A sheet can carry the first without the second — which is why one sits beside the ratings and the other under mounting.
| Line on the datasheet | What it was tested for | What it stays silent on |
|---|---|---|
| IP66 (IEC 60529) | Powerful jets: 12.5 mm nozzle, 100 L/min, at least 3 min | Sun, cold, corrosion, weeks of thermal cycling |
| IP67 (IEC 60529) | Immersion: 1 m for 30 min | The jet test; outdoor duty |
| Type 4X (NEMA 250) | Rain, hose-down, external icing, plus corrosion: 200 h salt spray (UL 50E Table 5-1D) | Your mounting, gasket torque and cable entry |
| Environment statement | The maker's stated duty in words: ambient range, sun, intended locations | Nothing — this is the line you buy from |
Buy from the last row. The three codes above it describe tests; only the statement describes the years between them.
What do the IP codes actually test?
IEC 60529 scores two things: dust, where the first digit 6 means dust-tight, and water, where the second digit 6 is powerful jets and 7 is 30 min of immersion — and the water tests run separately, never added together.
IP66 drives water through a 12.5 mm nozzle at 100 L/min against every surface for at least 3 min; IP67 lays the box 1 m under still water for 30 min. Both run once, on a new assembly with the gasket as built. Neither test runs the other: a unit marked IP67 alone has never stood under the jets, and hose-down or driving rain is a jet condition, not an immersion one. If your datasheet prints only IP67 and a washdown hose lives nearby, get the jet digit in writing before you order.
The digit-by-digit meanings, nozzle sizes and flow rates sit in the IP rating chart.
What does NEMA 250 Type 4X add beyond water?
Type 4X is written for outdoor use: it takes the Type 4 water tests — rain, hose-down and external icing — and adds a corrosion duty, which UL 50E Table 5-1D proves with 200 hours of salt spray beside an AISI 304 stainless specimen.
That corrosion element is exactly what an outdoor installation leans on, and it is the part a partial claim leaves out. Read 'parts of Type 4X, water ingress and gasket test' as: the water portions were run, the corrosion duty was not. A sealed camera can pass every water test and still lose its seal to one coastal winter, and the salt spray test is the part of the standard written for that failure.
One more boundary: you cannot convert a passing IP test into a Type. The two standards use different rigs, and the pairing on a nameplate is the maker's to earn; the NEMA 4X vs IP66 guide walks the differences.
What does the datasheet's outdoor statement cover that the tests miss?
The environment statement covers the three killers the ingress tests never touch — temperature range, sun on gaskets and housings, and condensation duty — so that line, not the code, decides whether the unit survives your site.
Read the sheet in this order:
- Ambient range. An outdoor line looks like −30 to +50 °C [−22 to +122 °F]; the floor is the number that matters on your coldest night. If the stated floor sits above it, the unit is not for your tower, whatever the code says.
- Sun. UV hardens elastomer gaskets and embrittles plastics; compression set opens the seal path years before any lab rig would catch it.
- Condensation duty. Some makers fit a heater or desiccant and say so; others expect a dry location. Fog inside a sealed unit is a duty question unless the sheet claims outdoor use.
- Mounting. 'Inside vehicles and rolling stock' is a positive statement of intended duty. Where the intended-use line names no outdoor work, the ingress codes do not supply it.
Buy on the positive statement: hunt for 'outdoor' in the intended-use line the way you hunt for a torque value in a drawing. When the sheet names a vehicle cab instead of a tower, mount the unit in a rated enclosure instead. The outdoor-rating checklist shows which marks to trust, and the outdoor enclosure guide covers the site-side choices.
Why does a sealed IP67 box still collect water over weeks?
Breathing moves the water, not a leak: a night that cools the box by 10 °C shrinks the trapped air by ΔT/T in kelvin — 10 K ÷ 298 K = 3.4 % — so a sealed box inhales that share of outdoor air through its gasket path.
Worked example — a 20 × 16 × 8 in wall-mount box:
- Volume: 20 × 16 × 8 in = 2,560 in³, and 1 in³ = 16.4 mL, so the box holds about 42 L.
- A clear night drops it from 25 °C to 10 °C, a 15 K swing. Share drawn in: 15 K ÷ 298 K = 5.0 %.
- Air pulled through the gasket: 0.050 × 42 L = 2.1 L per night.
- Summer air at 25 °C and 80 % relative humidity carries about 18 g of water per m³, so each night brings 0.0021 m³ × 18 g/m³ ≈ 0.04 g.
- Over a 90-night season that is about 3.4 g of liquid water — enough to fog the window every morning and run down the wall.
The gasket is a path, not a wall: pressure has to equalize somewhere, and when the seal is the only way in, the box drinks on every swing. This cycle is why a rating alone cannot stop condensation; the sealed-box article follows it hour by hour.
How do you keep an outdoor box dry for good?
Give the box a rated breather and, where the load needs one, a small heater: an IP66-rated vent lets pressure cross a membrane instead of the gasket, and heat held a few kelvin above the dew point keeps the window clear.
Fit the breather as its maker describes and the assembly keeps NEMA 4X / IP66; an unrated hole or louver drops the whole box to that part's rating, because the weakest part sets it. A breather-drain sits low in a side wall so condensate can leave. Size the vent area from box volume with the breather and drain guide, and see what the rating survives in the breather-vent article.
Where electronics live in the box, size an anti-condensation heater from volume and your site's dew point; the sizing article shows the arithmetic.
Enter below the unit with glands matched to the cable OD and rated IP66; water wicks along conductors as readily as it passes a tired gasket fixing the cable entry. Shave the swing itself where the site allows — shade from direct sun, because every kelvin of swing you remove is breathing you remove mounting without losing the rating.
What do you put on the order?
Order in this sequence: environment line first, then the rating pair, then the material, then breather, heater and glands — and on a US job the drawing carries the NEMA Type, because NEC 110.28 says IP ratings are not a substitute for enclosure Type ratings.
- Environment line names outdoor use and covers your coldest and hottest day: install as drawn and add the IP66 breather.
- Line names indoor, vehicle or rolling-stock duty: mount the unit inside a NEMA 4X / IP66 enclosure and enter below it with IP66 glands. That pairing is the fix, and it costs one enclosure.
- Salt air, brine or chemical splash: order 316L; its molybdenum buys pitting resistance where 304 pits 304 or 316L at a glance.
- US job with an inspector: the drawing names the Type number, and Table 110.28 matches each Type to the locations it suits NEMA enclosure types guide.
When the answer is 'put it in a proper box', the stainless size finder filters our wall-mount line from 6 × 4 × 4 in to 60 × 36 × 16 in outside (H × W × D), in 304 or 316L, with every cutout set by you. Delivery is 10 business days, counted from the order or, for custom work, from your approval of the drawing.
Questions
Does an IP67 mark cover hose-down or driving rain?
No. IEC 60529 runs the water tests separately: IP67 is 1 m of still water for 30 min, while IP66 is jets through a 12.5 mm nozzle at 100 L/min for at least 3 min. A box that passed only immersion has not passed the jets, so for hose-down or driving rain specify the jet digit on the datasheet — IP66 or IPX6 — instead of trusting the higher number.
Can I fit a breather to a NEMA 4X / IP66 box and keep the rating?
Yes, when the breather is itself rated IP66 and fitted as its maker describes; the assembly then keeps NEMA 4X / IP66. A plain drilled hole or an unrated louver drops the whole assembly to that part's rating. Size it for the breathing load: each 10 °C night pull moves about 3-4 % of the air volume, so a 42 L box draws roughly 1.4 L per swing.
Is a NEMA 250 Type 4X mark automatic proof of outdoor suitability?
Type 4X is written for outdoor use and adds a corrosion duty on top of the Type 4 water tests; UL 50E Table 5-1D proves it with 200 hours of salt spray beside an AISI 304 stainless specimen. The mark counts when the equipment maker applies the full standard to the whole assembly, mounting and cable entry included. A partial claim — 'parts of Type 4X' — leaves the corrosion duty out.
What changes for a coastal or salt-air site?
Order 316L stainless: its molybdenum raises pitting and crevice resistance to the chloride attack that salt air drives; 304 still holds most inland outdoor sites. Keep the rating pair NEMA 4X / IP66, fit an IP66-rated breather drain low in the wall, and add an anti-condensation heater, because a 15 °C night swing moves 5 % of a 42 L box's air and the fog follows.
