Quick answer: Condensation forms inside an electrical cabinet when a surface, often the roof panel, a cable gland or a cooled plate, drops below the dew point of the air inside. To stop it, first seal any path for rain or wash water, then either keep the cold surfaces warmer (a heater) or take water out of the air (a cabinet dehumidifier). Dehumidifiers drain the water out of the enclosure; heaters only move the condensation point.
Quick answer
- Wet only after rain or washing: it is ingress. Fix gaskets, glands and roof joints.
- Wet at dawn, after shutdown or near a cooling unit: it is condensation. Use a dehumidifier, a heater, or both.
- A sealed IP-rated cabinet still breathes through temperature changes, so it can still condense.
Why does an electrical cabinet get condensation?
Air always contains water vapor. When air touches a surface colder than its dew point, the vapor turns into liquid water on that surface. Cabinets hit this point in four common situations:
- Night cooling. An outdoor cabinet warms in the sun and cools fast after sunset; the roof panel drops below the dew point first and drips onto the equipment below.
- Shutdown. Equipment stops producing heat, the cabinet cools, and moisture that was harmless while it ran condenses.
- Cooling units. An air conditioner or heat exchanger creates a cold surface inside the cabinet.
- Breathing. Each daily warm-up and cool-down pushes air out and draws humid outdoor air back in through gaskets, glands and vents, even in an IP-rated enclosure. See why IP-rated enclosures can still condense.
How much water can condense?
More than most people expect. Air at 30 °C and 80 % RH holds about 24 g of water vapor per cubic metre. If the cabinet then cools to 15 °C, the air can hold only about 13 g/m³, so about 11 g of water per cubic metre condenses. Every warm-humid to cool cycle that draws in fresh air repeats the process, so water accumulates night after night.
| Cabinet air volume | Water condensed when 30 °C/80 % RH air cools to 15 °C |
|---|---|
| 0.2 m³ (wall-mounted control panel) | about 2 g |
| 1 m³ (floor-standing cabinet) | about 11 g |
| 30 m³ (20 ft container, free air volume) | about 330 g |
Values are calculated from the saturation vapor density of water at standard pressure; they show one full exchange of air.
What damage does it cause?
Condensation leads to corrosion of terminals and busbars, tracking across insulators, falling insulation resistance, nuisance tripping and false sensor readings. Salt or industrial pollutants dissolved in the water make all of these worse. Our article on corrosion control in electrical enclosures covers coastal and industrial sites.
How to stop condensation: four methods compared
| Method | What it does | Use it when | Limit |
|---|---|---|---|
| Seal the boundary | Stops rain, wash water and air leaks | Water appears after rain or washing; damaged gaskets or open knockouts | Does nothing about moisture already inside |
| Enclosure heater | Keeps surfaces above the dew point | Cold climates, small cabinets, short humid periods | Water stays in the cabinet; adds heat; needs power continuously in cold weather |
| Breather or membrane vent | Equalizes pressure, keeps out liquid water and dust | Sealed boxes that need pressure relief | Humid air still passes through; see membrane vents and condensation |
| Cabinet dehumidifier | Removes water vapor and drains it outside | Recurring condensation, humid or coastal sites, cabinets with cooling units, battery and switchgear cabinets | Needs a drain path and power |
Related: membrane vents and condensation.
Many outdoor cabinets use a dehumidifier as the main control and a small heater for very cold periods. Our guide to heater vs ventilation vs dehumidifier compares them in more detail.
How to choose a cabinet dehumidifier
- Measure first. Log inside air temperature, humidity and the temperature of the coldest surface for a few days, including nights. Compare the surface temperature with the dew point. Our dew point sensor placement guide shows where to put the sensors.
- Pick the technology by temperature and size.
- Peltier (thermoelectric): compact, no compressor, works in cold outdoor cabinets. Typical removal 0.5–1 L/day.
- Compressor: for larger cabinets, containers and high moisture loads. Typical removal 4–10 L/day.
- Check the power supply. AC 220–240 V or DC 24 V models fit most panels.
- Plan the drain. The water must leave the cabinet through a hose that falls to the outside, with a sealed penetration and frost protection outdoors.
- Connect alarms if needed. For unattended sites, choose a unit whose fault or humidity signal can reach the site controller.
ANTIS electrical cabinet dehumidifiers cover both technologies:
| Model | Type | Removal | Rating condition | Operating temperature | Supply |
|---|---|---|---|---|---|
| ADS-500ML | Peltier | 500 mL/day | 35 °C/85 % RH | −30 to +55 °C | AC 220–240 V / DC 24 V |
| ADS-1000ML | Peltier | 1,000 mL/day | 35 °C/85 % RH | −30 to +55 °C | AC 220 V / DC 24 V |
| ADS-100WB-01 | Compressor | 4 L/day | 30 °C/80 % RH | 5–40 °C | DC 24 V |
| ADS-100WB-06 | Compressor | 6 L/day | 30 °C/80 % RH | 5–40 °C (AC), 5–45 °C (DC) | AC 220 V / DC 24 V |
| ADS-10D | Compressor | 10 L/day | 30 °C/80 % RH | 5–40 °C | AC 220 V, 50 Hz |
| ADS-10DW2 | Compressor | 10 L/day | 30 °C/80 % RH | 5–40 °C | AC 220 V, 50 Hz |
Compare models within the same rating condition. For battery cabinets and containers, see our BESS dehumidifiers.
Installation tips
- Mount the dehumidifier low in the cabinet, where the drain can fall freely to the outlet, with its air inlet clear of cables.
- Seal the drain hose penetration and fit a trap or one-way valve so outside air cannot enter through it.
- Keep the humidity sensor away from heaters and the dehumidifier's own outlet.
- Close unused knockouts and replace hardened door gaskets at the same visit.
FAQ
Frequently asked questions
Why does my electrical panel have water inside but no visible leak?
It is almost certainly condensation. Check whether the water appears in the morning or after shutdown, and whether it collects under the roof panel or a cold component.
Is a heater or a dehumidifier better for an electrical cabinet?
A dehumidifier removes the water; a heater only keeps surfaces warm enough for water to stay in the air. In humid and coastal climates, a dehumidifier is usually the more reliable fix, with a heater added for very cold sites.
What humidity should an electrical cabinet be kept at?
Keep the dew point of the cabinet air below the temperature of its coldest surface, with a margin of a few degrees. Equipment manufacturers' manuals often state a maximum relative humidity, commonly non-condensing.
Does an IP65 cabinet need a dehumidifier?
Often, yes. IP65 keeps out jets of water and dust, but daily temperature cycling still draws humid air in through seals, and that moisture condenses inside.
References
- NIST, Thermophysical properties of water (saturation vapor pressure and density).
- IEC 60529, Degrees of protection provided by enclosures (IP Code).
- ASHRAE Handbook—Fundamentals, Psychrometrics.
