A connector can look completely dry and still fail after days in a humid environment.
A PCB may show no obvious corrosion, yet its insulation resistance has already shifted. A polymer enclosure may appear unchanged while moisture has gradually entered the material. A control module may pass visual inspection but behave differently when powered again.
That is the kind of failure IEC 60068-2-78 Test Cab is intended to investigate.
IEC 60068-2-78:2025 specifies a steady-state damp heat test for evaluating how components or equipment withstand high humidity during transportation, storage or use. The key idea is straightforward: the specimen is exposed to high humidity at a constant temperature, without condensation, for a specified period.
The method applies to small components as well as larger equipment, including heat-dissipating and non-heat-dissipating specimens. The current edition is IEC 60068-2-78:2025, Edition 3.0, which replaces the 2012 edition.
That sounds simple.
In practice, however, a valid Test Cab exposure depends on much more than entering a temperature and RH value into a chamber controller.
Specimen condition, thermal state, airflow, chamber loading, exposure duration, dew point, preconditioning and post-test measurements can all influence whether the result actually tells you something useful.
What Does IEC 60068-2-78 Actually Reproduce?
It is tempting to describe IEC 60068-2-78 simply as a “humidity test.”
That description misses an important part of the mechanism.
A better way to understand the exposure is:
CONSTANT TEMPERATURE
＋
HIGH RELATIVE HUMIDITY
＋
TIME
↓
PROLONGED MOISTURE EXPOSURE
↓
ABSORPTION / DIFFUSION / PENETRATION
↓
ELECTRICAL, MATERIAL OR FUNCTIONAL CHANGE
The important word is steady.
Unlike cyclic damp heat testing, Test Cab does not depend on repeatedly raising and lowering chamber temperature. The specimen remains in a controlled humid environment long enough for moisture-related effects to develop.
That distinction changes both how the test is run and what engineers should look for afterward.
A connector may show a change in contact resistance.
A PCB assembly may develop leakage paths.
An insulating material may absorb moisture.
A sensor may drift.
A control module may remain visually intact but show an electrical or functional difference.
The chamber provides the environment. The DUT tells the failure story.
No Condensation ≠ No Moisture Damage
This is probably the most important point to understand about IEC 60068-2-78.
Test Cab is intended to investigate high humidity at constant temperature without condensation on the specimen.
That does not mean the specimen remains unaffected.
Visible droplets are only one form of moisture exposure.
Water vapor can interact with materials even when no liquid water is visible on the product surface. A polymer can absorb moisture. An insulating surface can become more conductive. Moisture can migrate through coatings, gaps and interfaces.
For electronic products, this can eventually appear as:
Insulation Resistance ↓
Leakage Risk ↑
Contact Stability ↓
Material Properties Change
Electrical Performance Changes
Functional Reliability ↓
This becomes especially important when engineers rely too heavily on visual inspection after environmental testing.
Imagine two specimens.
The first comes out of the chamber with slight visible discoloration but still passes every required electrical measurement.
The second looks completely normal but its insulation resistance has moved outside the product limit.
Which one failed?
The answer is not determined by appearance alone.
It depends on the acceptance criteria defined before the test.
IEC 60068-2-78:2025 — What Changed?
The current IEC 60068-2-78:2025 is Edition 3.0 and replaces IEC 60068-2-78:2012.
This is a technical revision rather than a simple editorial update.
IEC identifies several significant changes in the 2025 edition, including revisions to test chamber requirements, severities and dew-point temperatures, temperature limits, preconditioning, explanatory figures and standardized test-report requirements.
For a laboratory, it is more useful to think about these changes according to what they affect.
What affects the chamber?
Updated chamber requirements and temperature limits mean that laboratories should review whether an existing setup satisfies the edition actually specified by the qualification program.
What affects the test program?
Severity, dew point and preconditioning affect how the specimen reaches and experiences the intended environment.
These are not merely reporting details. They can influence whether the exposure remains a true non-condensing steady-state damp heat test.
What affects the documentation?
The test-report requirements have also been revised.
A chamber graph alone cannot show whether the correct specimen, severity, preconditioning, operating state and evaluation criteria were used.
If your laboratory has a Test Cab recipe saved from a previous qualification, the first question should therefore not be:
“Can we reuse the same program?”
A better question is:
“Which parts of the test method around that program need to be reviewed for IEC 60068-2-78:2025?”
Test Severity Is More Than an RH Number
One of the easiest ways to oversimplify a damp heat steady state test is to describe it only by relative humidity.
For example:
“We test at high RH.”
That does not define the complete exposure.
A useful engineering model is:
TEST SEVERITY
TEMPERATURE
＋
RELATIVE HUMIDITY
＋
EXPOSURE DURATION
The 2025 edition includes revised severities and corresponding dew-point considerations.
This matters because two tests conducted at similar RH can still expose a DUT differently if temperature or duration changes.
A short exposure may reveal little.
A longer exposure may allow moisture to reach materials or interfaces that respond slowly.
Likewise, the same RH value at a different temperature does not represent exactly the same moisture condition.
The applicable severity should therefore come from the relevant product specification or qualification requirement—not from a generic chamber recipe copied from another product.
The requirement defines the test.
The chamber reproduces it.
Why Dew Point Matters in a Non-Condensing Test
If Test Cab is supposed to be non-condensing, dew point becomes important.
At a given combination of air temperature and relative humidity, the air has a corresponding dew-point temperature.
If a specimen surface becomes colder than that dew point, condensation can form.
Conceptually:
AIR TEMPERATURE + RH
↓
DEW POINT
Then compare it with the DUT surface:
DUT Surface > Dew Point
→ Non-condensing condition
DUT Surface < Dew Point
→ Condensation risk
This is one reason the thermal condition of the specimen matters during preconditioning, installation, environmental transitions and recovery.
A heavy metal enclosure may not change temperature as quickly as chamber air.
A cold specimen introduced directly into a humid environment may behave differently from a properly conditioned specimen.
A large fixture can also introduce local thermal behavior that is not obvious from the chamber controller.
For IEC 60068-2-78, unintended condensation can mean the DUT experiences a different moisture mechanism from the one Test Cab is intended to reproduce.
A Stable Chamber Setpoint Does Not Automatically Mean a Stable DUT Condition
This is where chamber specifications and real testing begin to separate.
Suppose the controller shows:
40°C / 93% RH
and both values appear stable.
Does that automatically prove every DUT is experiencing the intended condition?
Not necessarily.
The specimen itself introduces physical variables into the working space.
A large DUT can obstruct circulation.
Closely packed specimens can create sheltered areas.
Fixtures and shelves can alter airflow.
Powered electronics can release heat.
Cable routing can affect the test setup.
A large metal assembly may respond more slowly than chamber air.
This means the actual test environment has to be considered together with the specimen load.
A chamber that performs well when empty may behave differently when filled with large products or equipment generating significant heat.
So instead of asking only:
“What is the maximum RH?”
ask:
How large is the DUT?
How many specimens will be tested together?
How much space remains for air circulation?
Is the specimen powered?
How much heat does it generate?
Where will cables and measurement connections enter the chamber?
The test is performed on the specimen—not on the controller display.
IEC 60068-2-78 Test Procedure: A Practical Workflow
The exact procedure should follow the applicable IEC 60068-2-78 edition together with the relevant product specification.
From a laboratory planning perspective, however, the workflow can be organized into eight practical stages.
1. Define the Requirement
Before programming the chamber, confirm the applicable standard edition, required severity, exposure duration, specimen operating state, measurements and acceptance criteria.
This is where a good test begins.
2. Establish the Baseline
Record the DUT condition before exposure.
Depending on the product, useful baseline data may include:
visual condition, insulation resistance, contact resistance, electrical output, functional operation or other product-specific characteristics.
3. Precondition the Specimen
Apply the required specimen preconditioning before the main exposure.
This deserves particular attention when reviewing procedures for the 2025 edition because IEC specifically identifies a defined preconditioning procedure among its technical revisions.
4. Install the DUT
Position specimens so that they do not unnecessarily block circulation.
Do not treat every empty shelf position as usable test capacity.
The DUT needs appropriate space around it for environmental control.
5. Establish the Required Condition
Bring the chamber and specimen to the specified environment according to the required procedure while avoiding unintended condensation.
6. Maintain the Damp Heat Exposure
Hold the required steady damp heat environment for the specified duration.
Record environmental data according to the test plan.
7. Recover
After exposure, follow the required recovery procedure.
The time between exposure and measurement can matter, particularly for moisture-sensitive electrical characteristics.
8. Evaluate
Compare the specimen against its baseline and predefined acceptance criteria.
The useful result is not:
“The chamber ran for 96 hours.”
The useful result is:
“What changed in the DUT after the specified damp heat exposure?”
What Products Are Commonly Evaluated?
IEC 60068-2-78 can be applied to small components, small equipment and larger equipment, including heat-dissipating and non-heat-dissipating specimens.
For engineers, however, a more useful question is:
Where can moisture have an effect, and what should we check afterward?
| Product | Moisture-Sensitive Area | What Engineers May Check |
|---|---|---|
| PCB / PCBA | Surface contamination, coating, laminate, component interfaces | Insulation resistance, leakage, function |
| Connector | Contact interface, exposed metal, polymer housing | Contact resistance, signal stability |
| Automotive ECU | PCB, connectors, enclosure interfaces | Communication, electrical output, function |
| Relay / Switch | Contacts, terminals, insulating structures | Contact behavior, electrical performance |
| Power Supply / Charger | Insulation system, PCB, transformer, interfaces | Leakage, insulation, output |
| Sensor | Electronics, sensing interface, package materials | Drift, output stability, function |
| Telecom Module | PCB, connectors, enclosure | Communication stability, electrical function |
| Industrial Controller | PCB, terminals, display, internal wiring | Functional and electrical reliability |
This is why a single generic pass/fail rule rarely works across every Test Cab application.
A connector and a PCB can sit in the same chamber.
They are not necessarily being evaluated for the same failure mechanism.
IEC 60068-2-78 vs IEC 60068-2-30
Both standards address damp heat.
They should not be treated as interchangeable versions of the same test.
| IEC 60068-2-78 | IEC 60068-2-30 | |
|---|---|---|
| Test | Cab | Db |
| Method | Damp heat, steady state | Damp heat, cyclic |
| Temperature | Constant | Cyclic |
| Humidity | High | High |
| Condensation | Avoided | Can be part of the environmental mechanism |
| Primary Stress | Prolonged moisture exposure | Temperature cycling + humidity + specimen thermal response |
In practical terms:
IEC 60068-2-78 asks what happens when high humidity stays.
IEC 60068-2-30 asks what happens when high humidity is combined with cyclic temperature change.
Do not select one simply because it appears “more severe.”
Select the method required by the product specification and the environmental mechanism being investigated.
For cyclic damp heat testing, refer to the separate IEC 60068-2-30 guide rather than treating Test Db and Test Cab as equivalent methods.
Where Do Test Cab Results Commonly Go Wrong?
The test does not normally go wrong because somebody forgot how to enter a temperature.
The problems are often less obvious.
A crowded chamber can create poor airflow around some specimens.
A DUT with significant heat dissipation can disturb local conditions.
A specimen introduced at the wrong thermal state can experience unintended condensation.
A laboratory can complete a multi-day exposure only to discover that no meaningful electrical baseline was recorded.
Another common mistake is judging test validity only from the chamber graph.
The graph is important.
But it cannot tell you whether the specimens were installed correctly, whether the DUT was operated in the intended state, or whether post-test measurements were performed according to the qualification plan.
A useful environmental test needs both:
ENVIRONMENTAL EVIDENCE
and
PRODUCT EVIDENCE
What Should an IEC 60068-2-78 Test Chamber Be Able to Do?
Only at this point does chamber selection become useful.
For Test Cab, the goal is not to buy the chamber with the widest headline specification.
The goal is to reproduce the required environment around the actual DUT.
Temperature and RH Operating Envelope
A chamber may list a maximum temperature and a maximum RH, but those two maximum values should not automatically be assumed to be available simultaneously under every operating condition.
Always verify the required temperature/RH combination.
Usable Working Space
The DUT, fixture, cables and airflow clearances all occupy space.
Nominal chamber volume is not the same as practical loaded test capacity.
Performance Under Specimen Load
Large, densely packed or heat-generating specimens can affect chamber response.
Chamber suitability should therefore be evaluated around the actual test load rather than only empty-space performance.
Air Circulation
Uniform environmental conditions depend on adequate circulation around the specimen.
Product arrangement matters.
Powered Heat Load
If the DUT operates during exposure, its heat output should be considered when evaluating chamber performance.
Humidification and Water Management
Long-duration damp heat testing places continuous demands on the humidity-generation system.
Stable operation and appropriate maintenance therefore matter.
Data Recording
Environmental data should support the qualification record rather than serve only as a live controller display.
The principle is simple:
Select the chamber based on the condition required at the DUT—not only on the maximum values printed on the specification sheet.
Matching the ITM-LAB GDJS to IEC 60068-2-78
For applications requiring controlled temperature and humidity, the GDJS Series Programmable Constant Humidity and Temperature Test Chamber is the primary ITM-LAB platform for IEC 60068-2-78 testing.
ITM-LAB GDJS Temperature & Humidity Test Chamber
The GDJS series is currently offered with multiple temperature configurations extending from −40°C or −70°C to +150°C, a stated humidity range of 20% to 98% RH, and capacities from 100 L to 1000 L. ITM-LAB also explicitly lists IEC 60068-2-78 among the supported IEC 60068 methods for the series.
The capacity decision should come after understanding the DUT.
For compact electronic components or assemblies, a smaller chamber may provide sufficient working space.
Multiple PCB assemblies, automotive modules or larger test batches may require more working volume.
Large assemblies or multi-DUT loading may require a larger configuration.
But physical fit is only the first check.
There still needs to be appropriate space around the specimens for airflow and environmental control.
Before selecting a GDJS configuration, define:
DUT dimensions and quantity
Required temperature and RH
Exposure duration
Powered or unpowered condition
Estimated heat dissipation
Fixture arrangement
Cable routing
Required monitoring points
Then verify that the required Test Cab condition falls inside the applicable temperature/RH operating envelope for the selected chamber configuration.
This is more reliable than choosing a chamber simply because:
“The DUT fits inside.”
IEC 60068-2-78 Test Chamber Selection Roadmap
Example: Testing an Automotive Electronic Control Module
Consider an ECU scheduled for steady damp heat qualification.
A weak test plan might read:
“Put four ECUs in the humidity chamber and run the standard condition.”
That sentence leaves several unanswered questions.
How are the units spaced?
Are they energized?
How much heat do they generate?
Which electrical functions are checked before exposure?
Which measurements are repeated afterward?
What constitutes failure?
A better test plan starts with the DUT.
The laboratory records the ECU dimensions, mass, connector arrangement and operating state.
Baseline communication and electrical performance are measured.
The modules are installed with sufficient clearance for air circulation.
The required Test Cab severity and exposure duration are programmed according to the applicable qualification requirement.
Environmental data is recorded during exposure.
After the specified recovery, the same electrical and functional checks are repeated.
Now the test answers a meaningful question:
Did prolonged non-condensing damp heat exposure change the ECU's electrical or functional performance?
That tells an engineer far more than:
“Humidity test completed.”
What Should Be Recorded in the Test Report?
IEC identifies standardized test-report requirements as one of the areas revised in the 2025 edition.
The exact report should follow the applicable standard and product specification, but a useful laboratory record should connect the environment with the specimen.
Depending on the test program, relevant information may include the standard and edition, specimen identification, severity, preconditioning, exposure duration, specimen arrangement, operating state, environmental records, recovery procedure, required measurements, observed changes and final acceptance result.
The key point is traceability.
If another engineer reviews the report six months later, they should be able to understand not only what the chamber did, but also what the DUT experienced and how PASS or FAIL was determined.
FAQ
- What is IEC 60068-2-78?
IEC 60068-2-78 specifies Test Cab: Damp heat, steady state, a method for evaluating components or equipment under prolonged high humidity at constant temperature without condensation. The current edition is IEC 60068-2-78:2025, Edition 3.0.
- Does IEC 60068-2-78 require condensation?
No. Test Cab is intended to investigate high humidity at constant temperature without condensation on the specimen. Moisture-related degradation can still occur even when no visible droplets are present.
- What is the difference between IEC 60068-2-78 and IEC 60068-2-30?
IEC 60068-2-78 is a steady-state damp heat test, while IEC 60068-2-30 is a cyclic damp heat test. Test Cab focuses on prolonged non-condensing humidity exposure; Test Db introduces cyclic temperature changes and associated specimen thermal effects.
- What products can be tested to IEC 60068-2-78?
The method can be applied to components and larger equipment, including heat-dissipating and non-heat-dissipating specimens. Typical applications include PCBs, connectors, automotive electronics, sensors, power electronics, telecom equipment and industrial controllers.
- Which ITM-LAB chamber can be used for IEC 60068-2-78?
The GDJS Series Programmable Constant Humidity and Temperature Test Chamber is the primary ITM-LAB solution for Test Cab applications requiring controlled temperature and humidity. The final configuration should be selected according to the required temperature/RH condition, DUT dimensions, specimen quantity, operating state and heat load.
Conclusion
IEC 60068-2-78 can be easy to underestimate because the chamber condition looks simple.
There is no rapid temperature change.
There is no intentional condensation.
There may be no dramatic visible failure.
But that is exactly why the test is useful.
A product can look dry while moisture gradually affects its insulation, contacts, coatings, interfaces or electrical performance.
A good Test Cab plan therefore does not begin with:
“Which humidity chamber should we buy?”
It begins with:
What moisture-related change are we trying to reveal, under which defined steady-state condition, and how will we know whether the DUT passed?
Once those questions are answered, chamber selection becomes much more straightforward.
For IEC 60068-2-78 applications, a suitable GDJS configuration should be selected around the actual DUT dimensions, quantity, required temperature/RH condition, exposure duration, operating state and heat load—not simply around nominal chamber capacity.
Explore ITM-LAB Environmental Test Chambers
If you are configuring a chamber for Test Cab, provide the DUT size, quantity, required temperature/RH, exposure duration, operating state and estimated heat load. These details make it possible to evaluate whether a standard GDJS configuration is suitable or whether the working space or thermal load requires a different solution.
