Define the environment before choosing the equipment

Hello everyone. Even when a device has the right electrical ratings, temperature, humidity, dust, corrosion and vibration can determine its reliability in service. IEC 60721 is a series of IEC standards that classifies the environmental conditions encountered by electrical and electronic products. It gives manufacturers, designers and users a shared technical language for describing those conditions.

This approach helps when selecting PLCs and accessories, HMI operator panels, variable frequency drives and power supplies. A statement such as “complies with IEC 60721” needs further detail: the relevant part, edition, classes and additional manufacturer limits should be specified together.

How the series is organised

IEC 60721-1 defines environmental parameters and their severity levels. The IEC 60721-2 family addresses conditions occurring in nature; for example, IEC 60721-2-1 classifies outdoor climates in terms of temperature and humidity. These data provide background information when determining the environment a product will actually experience.

IEC 60721-3 application classes group conditions according to the situation in which a product is used. IEC 60721-3-1 covers storage, IEC 60721-3-2 covers transportation and handling, IEC 60721-3-3 covers stationary use at weatherprotected locations, and IEC 60721-3-4 covers stationary use at locations without weather protection. IEC 60721-3-7 addresses portable and non-stationary use. More than one part may apply during a product’s life cycle.

A weatherprotected location does not necessarily have controlled temperature and humidity. A production area sheltered from rain can still experience temperature changes, moisture, process contaminants and mechanical stresses. Conditions outside an enclosure can also differ from those around its components; IEC 60721-3-9 addresses microclimates inside products.

What a class code tells you

Codes such as 3K22 identify particular environmental classes in technical documentation. Within IEC 60721-3-3, for example, K identifies climatic conditions, M identifies mechanical conditions, and S identifies mechanically active substances such as dust and sand. A climatic class does not also establish resistance to vibration or contaminants; the relevant groups must be assessed separately.

Do not treat the number at the end of a code as a general quality score. Whether one class fully encompasses another depends on the tables and explanations in the applicable edition. Read the class code alongside the stated limits for temperature, relative humidity, condensation, pressure and installation.

Assess temperature and humidity together

The room temperature measured beside a cabinet may differ from the temperature at a drive’s cooling air inlet. Equipment losses, installation clearances, airflow and clogged filters can change local conditions. Alongside the permitted operating range, check the manufacturer’s derating requirements, mounting orientation and altitude limits.

Relative humidity measured by a humidity sensor must be interpreted together with temperature. When cold equipment enters a warm, humid area, condensation can form if its surface temperature remains below the dew point. A “non-condensing” requirement means that the stated humidity range does not guarantee safe conditions through every temperature transition.

The difference between a temperature sensor and a thermostat matters when separating measurement from switching. Suitable temperature controllers and humidity-controlled enclosure heating can help reduce condensation, depending on the design. Solutions such as PID humidity control should be assessed against the measured variable and the available dehumidification or humidification equipment; PID is not required in every cabinet.

Dust, chemical exposure and vibration

For dust, conductivity and interaction with moisture matter as well as the amount present. Salt-laden air or process gases can corrode connections and circuit boards. Protective board coatings can help in specified conditions, but they do not replace suitable enclosures, clean air, filter maintenance or compliance with the manufacturer’s environmental limits.

Continuous vibration and individual shocks require separate mechanical assessment. The mounting surface, fasteners and cable support can affect exposure. A shock rating stated for equipment in its shipping packaging does not establish the same resistance while it operates on a machine.

Environmental classes and IP ratings

An IP protection rating under IEC 60529 describes enclosure protection against access to hazardous parts, solid foreign objects and water ingress. IEC 60721 classifies environmental conditions. Consequently, an IP rating does not fully describe resistance to temperature, condensation, corrosion or vibration.

For example, an IP20 device may be intended for installation inside a suitable cabinet. Enclosure ratings such as IP65 and IP66 do not establish suitability for every climate or chemical environment. Internal heat accumulation and condensation risks still need to be assessed and controlled.

From environmental classification to testing

IEC 60721 classifies the environment; IEC 60068 environmental testing standards define test methods. Among the relevant correlation documents, IEC TS 60721-4-3:2023 relates classes for stationary use at weatherprotected locations to IEC 60068-2 tests. Check that the editions used for classification and test guidance are compatible.

A verification plan should specify test severity, duration, number of cycles, mounting arrangement, whether the equipment is powered, and acceptance criteria. When choosing a laboratory, examine its ISO/IEC 17025 scope and competence for the relevant tests. Assigning an environmental class does not itself demonstrate a successful test or a particular service life.

Preparing a practical specification

Consider a drive cabinet for a site near the coast. Separate storage and shipping conditions from the operating environment. Record internal and external temperatures, humidity, condensation risks, salt and process exposure, altitude and vibration. Select the relevant environmental classes, then compare them with the manufacturer’s product data. Drive-specific product requirements in the IEC 61800 series also need separate consideration.

The purchasing specification should bring together the standard part and edition, environmental classes, additional numerical limits, protective measures and required verification records. Plan maintenance for filters, seals, fans and humidity controls after commissioning. This connects environmental classification with equipment selection and the conditions maintained during operation.

Related topics

To develop the environmental specification further, explore the guide to applying environmental classes, IP protection explanations and environmental testing section.