Damp heat, steady state (Test Cab) - long-term humidity without condensation.
A method for testing the ability of components and equipment to withstand transport, storage and use under high humidity. It reproduces prolonged exposure to humid air at constant temperature without condensation on the specimen for a specified time.
It applies to both small components and large equipment, whether heat-dissipating or not.
The test demonstrates that insulating materials, coatings and connections withstand prolonged moisture saturation (absorption, diffusion, degradation of insulation resistance) under steady conditions. Unlike Test Db, the method maintains constant conditions and excludes condensation, so it does not cover enclosure “breathing” and capillary water ingress caused by temperature changes.
A datasheet entry without temperature, humidity and exposure time does not define severity; the combination is prescribed by the product standard.
The chamber and measuring system ensure that condensate from walls and ceiling does not fall on specimens; conductivity of water used for humidification does not exceed 20 µS/cm (2012 edition). The specimen is placed in the chamber, temperature is set first, then humidity is brought to the specified severity within 2 h; condensation on the specimen is avoided throughout the test.
Severity is the combination of temperature, relative humidity and exposure time: 30 °C ±2 K or 40 °C ±2 K at 93 ±3% RH or 85 ±3% RH, for 12 h, 16 h, 24 h, 2, 4, 10, 21 or 56 days (2012 edition). Initial measurements are performed before testing, followed by recovery and final measurements.
The 2025 edition changed chamber requirements, added dew-point temperatures to severity, replaced temperature tolerances with limits and added a specified pre-conditioning procedure.
Look for temperature (30/40 °C), humidity (85/93% RH) and duration in days; “40 °C / 93% RH / 56 days” is meaningful, the standard number alone is not. Check whether the manufacturer cites the 2012 or 2025 edition - the 2025 edition supplements severity with dew-point temperatures.
