💧 Test Cab — damp heat, steady state — PN-EN IEC 60068-2-78

Electronics and EMC PN-EN 60068-2-78

Overview

A NOTE AT THE OUTSET, BECAUSE IT CONCERNS EVERY ACCREDITATION SCOPE WITH THIS STANDARD: ON 9 SEPTEMBER 2026 THE EDITION CHANGED AND THE DESIGNATION CHANGED. The edition PN-EN 60068-2-78:2013-11 was withdrawn on that day and replaced by PN-EN IEC 60068-2-78:2026-09 (English-language version), implementing EN IEC 60068-2-78:2025 and IEC 60068-2-78:2025 as identical. The IEC element was added to the new designation — the number "PN-EN 60068-2-78" without this element now points to the withdrawn edition. A laboratory that has in its accreditation scope a line with "PN-EN 60068-2-78:2013-11" therefore cites a standard withdrawn thirteen days before this entry was drawn up (state on 22-09-2026). This does not mean that the test has ceased to be valid — it means that at the next update of the scope the number and date must be corrected, TOGETHER with the IEC element.

WHAT WE DO NOT KNOW ABOUT THE NEW EDITION AND DO NOT PRETEND TO KNOW. The content of the method described below comes from the IEC 60068-2-78:2012 edition — the one implemented by the withdrawn PN-EN 60068-2-78:2013-11. We did not have the text of the 2025 edition. Whether the severity table, the durations or the chamber requirements have changed in it, we have not checked, and we assume nothing either way. Everything below should be read as a description of the 2012 edition.

SCOPE AND OBJECT, QUOTED FROM THE TEXT OF THE 2012 EDITION (clause 1): "This part of IEC 60068 establishes a test method for determining the ability of components or equipment to withstand transportation, storage and use under conditions of high humidity. The object of this standard is to investigate the effect of high humidity at constant temperature WITHOUT CONDENSATION on a specimen over a prescribed period." WITHOUT CONDENSATION — THAT IS THE WHOLE DIFFERENCE FROM THE NEIGHBOURING TEST. CYCLIC damp heat (Test Db according to PN-EN 60068-2-30; the current edition PN-EN IEC 60068-2-30:2026-09 exists in the PKN catalogue ONLY IN THE ENGLISH-LANGUAGE VERSION — a Polish-language version exists only for the 2008 edition, which has been withdrawn; reading of 22.09.2026) consists of a temperature change chosen so that water CONDENSES on the specimen; STEADY-STATE damp heat examines the effect of the absorption and diffusion of moisture at a temperature kept constant, and condensation is avoided. That is why Test Cab does not and cannot have a "cycle": any sentence that attributes a 12 + 12 h cycle to it is misleading — that is a parameter of the cyclic test.

THE SEVERITY IS CHOSEN FROM A SHORT MENU — AND HERE TOO THE PRODUCT SPECIFICATION DECIDES. Clause 4.2 of the 2012 edition says: "The test severity is defined by a combination of temperature, relative humidity (RH) and total test duration. UNLESS OTHERWISE SPECIFIED IN THE RELEVANT SPECIFICATION, temperature and RH severities may be selected from the following" — after which Table 1 gives four pairs: 30 ± 2 °C at 93 ± 3 % RH, 30 ± 2 °C at 85 ± 3 % RH, 40 ± 2 °C at 93 ± 3 % RH and 40 ± 2 °C at 85 ± 3 % RH. Recommended durations: 12 h, 16 h, 24 h and 2, 4, 10, 21 or 56 days. IN THE WHOLE STANDARD (11 pages of the 2012 edition) the phrase "the relevant specification" occurs 15 times. Just as with Test Fc: the standard gives the way of conducting the test and a set of values to choose from, and the product document chooses from them and adds the assessment criterion.

WHY A TEMPERATURE TOLERANCE OF ±2 K DOES NOT MEAN THAT TEMPERATURES IN THE CHAMBER MAY DRIFT APART AT WILL. The standard explains this in clause 4.2, and it is something easily overlooked: "The total temperature tolerance of ±2 K is intended to take account of absolute errors in the measurement, slow changes of temperature and temperature variations of the working space. However, in order to maintain the RH within the required tolerances, it is necessary to keep the temperature DIFFERENCE BETWEEN ANY TWO POINTS in the working space at any moment within narrower limits. The required humidity conditions will not be achieved if such temperature differences exceed 1 K." The standard adds that maintaining the humidity may require short-term fluctuations to be limited to ±0.5 K. That is: ±2 K describes uncertainty and slow changes, while the simultaneous DIFFERENCE between two points of the working space must not exceed 1 K — because relative humidity depends on the local temperature, and temperatures drifting apart make the humidity drift apart.

WHAT THE STANDARD REQUIRES OF THE CHAMBER ITSELF (clause 4.1) — these requirements decide on the reliability of the result more than the severity figures: condensed water is drained from the chamber and not reused unless it has been purified; condensate from the walls and ceiling must not drip onto the specimen; the water maintaining the humidity has an electrical conductivity not greater than 20 µS/cm; the specimen must not be exposed to radiant heat from the chamber's conditioning equipment; injected moisture is supplied away from the specimen and not directly onto it; the volume of the chamber is at least FIVE TIMES the total volume of the specimens tested. The chamber is to be built and verified in accordance with IEC 60068-3-6.

Method principle

The specimen is placed in a climatic chamber and kept for a specified time in air at a constant, elevated temperature and high relative humidity, without allowing water to condense on the specimen. The effects of the absorption and diffusion of moisture and water vapour are assessed — by visual inspection and electrical and mechanical checks before the test, possibly during it, and after recovery to standard conditions.

Applications

• Electronic components and subassemblies — assessment of the effects of long-term humidity: water absorption by insulating materials, decrease of insulation resistance, contact corrosion
• Equipment intended for transport and storage in a humid climate
• Equipment of alarm and fire protection systems — product standards of the EN 54 series cite this test as part of the test programme
• Railway equipment and mobile machinery
• Heat-dissipating products — the standard applies to both heat-dissipating and non-heat-dissipating specimens
• Large and small equipment — the scope covers both components and large equipment

Key parameters

Standard

Standard number

PN-EN IEC 60068-2-78:2026-09 (wersja angielska; wprowadza EN IEC 60068-2-78:2025 [IDT], IEC 60068-2-78:2025 [IDT])

Title (PL)

Badania środowiskowe — Część 2-78: Próby — Próba Cab: Wilgotne gorąco stałe

Title (EN)

Environmental testing — Part 2-78: Tests — Test Cab: Damp heat, steady state

Step-by-step procedure

1. Establishing the severity and conditions from the product specification

   The temperature, relative humidity and duration are read, as well as the state of the specimen (powered or not, packaged or not), the type of specimen (heat-dissipating or not), the recovery conditions and the extent of the measurements.

2. Preconditioning (if required)

   The standard provides for it only when the product specification demands it.

3. Initial measurements

   The specimen is inspected visually and checked electrically and mechanically to the extent required by the specification.

4. Introducing the specimen into the chamber

   The specimen is introduced unpacked, switched off and ready for operation — or otherwise, if the specification so states. Introduction into a chamber already brought to the test conditions is permissible only when the specification allows it, and always without allowing condensation; for small specimens this is achieved by preheating them to the chamber temperature.

5. Bringing up the temperature, then the humidity

   First the specified temperature is established — by controlling the temperature of the specimen or by waiting until the specimen reaches it — and only then is the humidity brought up. The order matters here: the reverse leads to water condensing on the cooler specimen.

6. Reaching the specified humidity

   The humidity is brought to the specified value within not more than 2 hours.

7. Exposure

   The specimen is kept under the specified conditions for the time given in the specification. THE TIME IS COUNTED FROM THE MOMENT THE SPECIFIED CONDITIONS ARE REACHED — not from the introduction of the specimen into the chamber. The specification also determines whether and when the specimen is to operate.

8. Intermediate measurements (if required)

   They are made at the moments indicated by the specification, and the specimen must NOT be removed from the chamber for this purpose.

9. Recovery to standard conditions

   After exposure and before the final measurements, a recovery procedure is applied. Its method and time are prescribed by the product specification; the recovery conditions themselves are described in IEC 60068-1.

10. Final measurements

    The visual inspection and the electrical and mechanical checks are repeated to the extent required by the specification.

11. Report

    The standard lists the content of the report, including: the type of test (Cab), the edition of the standard, a description of the specimen, identification of the chamber, uncertainties of the measuring system, calibration data, the REQUIRED severities (from the specification) and the conditions ACTUALLY achieved. The distinction between "required" and "actual" is explicit in the standard, and the report is to give both.

Required equipment and apparatus

Reagents, media and consumables

Health and safety (OHS)

• The chamber remains heated and humid throughout the test, which is counted in days — opening it during the test disturbs the conditions and risks steam burns
• Condensate in the chamber and in the drainage system promotes the growth of microorganisms — the water must not be recirculated without purification
• Specimens powered during the test are live in a high-humidity atmosphere — risk of electric shock and short circuits through surface moisture
• After the end of the test, the specimen may have reduced insulation resistance until recovery is complete — carry out electrical measurements on this assumption
• Heat-dissipating products change the conditions around them — determine the arrangement of sensors and the clearances before the test, not during it

Frequently asked questions