Quick answer: An IP65 enclosure is dust-tight and protected against water jets under IEC 60529, but water vapour can still enter and condense during day–night temperature cycles. Control it with deliberate venting and drainage, sealing of cable entries, and active moisture control (heater or cabinet dehumidifier) where needed.
An IP rating tells you how well an enclosure keeps out solid particles and liquid water. As an enclosure heats by day and cools at night, the air inside expands and contracts, pushing air out and drawing humid outside air in through seals, glands and vents. That moisture condenses on the cold walls and roof at night and has no easy way out, so sealed enclosures can collect water over time.
Quick answer
- IP rating = protection against dust and liquid water, not vapour.
- Day–night cycles make enclosures "breathe" humid air in.
- Fix: drain/vent at the bottom, sealed glands, heater or cabinet dehumidifier.
What the IP code means
| Digit | Meaning | Examples |
|---|---|---|
| First (0–6) | Protection against solids | 5 = dust-protected, 6 = dust-tight |
| Second (0–9) | Protection against water | 5 = water jets, 6 = powerful jets, 7 = temporary immersion |
IEC 60529 defines the code (IEC 60529). None of the levels tests resistance to humid air entering and condensing.
How a "sealed" enclosure breathes: worked example
An outdoor enclosure with 0.5 m³ of air warms to 40 °C in the sun and cools to 15 °C at night.
- Air volume change from temperature: 288 K ÷ 313 K ≈ 0.92, so about 8 % of the air, roughly 40 litres, is drawn in as it cools.
- If outside air is 25 °C and 80 % RH (about 18 g of water per m³), each night brings in roughly 0.7 g of water.
- Over a year of daily cycles that is roughly 250 g, plus moisture from door openings and cable entries, and in a tight enclosure much of it stays inside.
Small, but enough to wet terminals and corrode contacts, especially near the cold roof where it condenses first.
Where moisture comes from inside
- Air drawn in by thermal cycling and pressure changes.
- Door openings during maintenance in humid weather.
- Cable entries and conduits, which can carry moisture or water from wet trenches; see cable trench moisture in switchgear.
- Cooling units with coils inside the enclosure, if their condensate is not drained properly.
- Moisture in materials (wood, insulation, paper) installed inside.
Control measures
| Measure | Purpose |
|---|---|
| Membrane vent and drain at the bottom | Equalise pressure through a controlled point; let liquid water out; see membrane vents |
| Seal cable entries and conduits | Stop moist air and water entering from trenches |
| Anti-condensation heater | Keep surfaces above dew point on cold nights |
| Cabinet dehumidifier | Remove water and lower the dew point; drain it outside |
| Cooling units with drained condensate | Keep coil water out of the enclosure |
| Door discipline | Limit openings in humid weather; close promptly |
Related: membrane vents.
Compare options in enclosure heater vs dehumidifier; for corrosion risk at coastal and industrial sites, see enclosure corrosion control. Our electrical cabinet dehumidifiers cover Peltier and compressor options.
Check the operating conditions, not the label
- Daily temperature range at the site, sun exposure and orientation.
- Outdoor humidity and seasonal dew points.
- Heat generated inside (and whether it switches off at night).
- How often the enclosure is opened.
FAQ
Frequently asked questions
Does an IP65 enclosure prevent condensation?
No. It keeps out dust and water jets, but humid air still enters as the enclosure heats and cools.
Should a sealed enclosure have a vent?
Often yes: a membrane vent and drain at the bottom control breathing and let condensed water escape.
How do I stop condensation in an outdoor electrical box?
Seal cable entries, add a vent and drain, and use a heater or cabinet dehumidifier to keep surfaces above the dew point.
Sources
- IEC 60529, Degrees of protection provided by enclosures (IP code).
- ASHRAE Handbook—Fundamentals, Psychrometrics.
