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The zones of the plant, the groups and the temperature classes of Gases

Wednesday, 31 March 2021

by Andrea Battauz, R&D Project Engineer di Cortem Group

1. Introduction
Among the various areas of application of the ATEX directive, the most widespread is the one concerning surface systems with the risk of the presence of an explosive atmosphere due to a mixture of air and flammable substances in the form of GAS or vapor. [1]
In this sector, installers and designers often ask themselves questions relating to the choice of the right electrical appliances to be installed on the plant site.
This choice depends on a series of parameters, among these we will deepen the probability that an explosive atmosphere can form (concept of zone) and the type of substances involved in this formation (concepts of GAS group and temperature class).


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1. Preface: the selection of the cable gland
In the plant concept it has always been of primary importance the physical separation between safe area and classified area. This concept was applied in the electric energy transport systems by means of cables buried in sand bed and then derived to the user (an electric motor or a junction box or an end user) with the use of a conduit tube suitable for the insertion of electrical cables (Freez-Moon) free from internal ridges and terminated on the end user through a physical separation made with explosion-proof sealing device (for example a sealing fitting).
With the advent of the IEC/EN 61241-0 and IEC/EN 60079-0 standards, as well as the IEC/EN 60079-1 standard, changed the concept of cable entry in electrical and electronic equipment suitable for areas with danger of explosion, allowing to have the cable entry with appropriate sealing cable gland.


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I should make a change to an already installed switchboard by adding new equipment inside that must interact with the production process, cable glands with relative holes and threads on one of the walls of the enclosure and two operators on the cover (button + indicator light), then drill and fillet the lid. How should I proceed for this change?

All the equipment and products placed on the market and installed have their own plate with a specific serial number, which refers to the construction project, and the reference to the certification.

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As required by IEC 60079-0 standard, each Ex product put on the market has its own identification plate with some information. Some data are required by the European Community directives, others are the consequence of the application of technical standards, specific for every equipment. 
Let's now look at the contents of a typical certificate plate for a product with Full Compliance certification, which must always be present on the equipment.
As we can see, we can find several fields on it with specific functions. Depending on the product and certification obtained, there are one or more types of certificates such as ATEX certification issued in the Community (EN) and IECEx certification (IEC) or other certification based on the country of destination of the product.
Let's look at the function of each field (reference) below.

Questions and Answers

Thursday, 27 February 2020

What is meant by maximum surface temperature and what can be the maximum surface temperature allowed for the correct operation of the equipment in presence of GAS, without causing an explosion just because the temperature is exceeded?

By surface temperature is meant the temperature detectable on the external surface of the equipment, a value that the system designer must carefully consider when choosing the temperature class. The maximum surface temperature of an equipment must never reach, even in fault conditions, the ignition temperature of the substance present in the dangerous atmosphere.


This value is normally reported on the certificate plate, where the temperature class "T ..." is reported for gases, while the temperature T ...° C is reported for dusts. 


For areas with the presence of gas, the equipment or materials are divided into temperature classes such as: 


Questions and answers

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