What cables to use in Ex zones

In these parts of the world, particularly in the European Union where the ATEX directive is applied, cables used in explosion-hazard zones are the same as those used in industrial installations. Therefore, contrary to popular belief, these cables do not have ATEX certification. However, the EN 60079-14 standard contains general requirements for their selection and use in explosion-hazard zones.  

ATEX cable requirements

According to the standard EN 60079-14 Explosive Atmospheres; Part 14: Electrical installations design, selection, and assembly, cables intended for use in explosion-hazard zones should meet the following conditions:

• In explosion-hazard zones, cables and wires are used in the same configuration as in industrial installations – except for intrinsically safe circuits,
• Separate cables should be run to individual devices,
• It is prohibited to use different voltages in the same cable,
• The cable design should prevent the migration of gases or vapors along the cable between conductors,
• Cables for intrinsically safe circuits should be shielded,
• Cables should be protected against mechanical damage, corrosion, UV radiation, and chemical factors.

NOTE 1: To eliminate the risk of excessive cable heating, which could be an ignition source, they must be used correctly.

NOTE 2: According to the ATEX USER directive, whether cables can be used in a specific hazardous area is ultimately confirmed by the Explosion Protection Document.

Why cables and wires for Ex zones do not require ATEX certification

Under the ATEX directive, properly used cables do not have their own sources of ignition and do not meet the definition of equipment, and therefore are not subject to conformity assessment under the ATEX directive. For this reason, so-called type examination certificates, commonly referred to as ATEX certificates, are not issued for them.

NOTE 3: This article refers to the requirements of the ATEX directive, which in turn refers to standards developed by IEC (International Electrotechnical Commission). In other parts of the world, there are different, often more stringent, requirements. This situation occurs, for example, in North America (where standards issued by the National Electrical Code – NEC are based) and Canada (where standards issued by the Canadian Electrical Code – CEC are based).

NOTE 4: The application of cables in explosion-hazard zones has also been discussed in other standards and documents issued by IEC, NEC, and CEC. Such a particular case is, for example, the recommendations for electrical installations at sea or on ships. These include documents such as:

• API RP14 (Recommended practice for the analysis, design, installation, and testing of basic surface safety systems for offshore production platforms),
• RP14FZ (Design and installation of electrical systems for fixed and floating offshore petroleum facilities for unclassified locations and class I, zone 0, zone 1, and zone 2).

Cable glands for Ex zones

The situation is entirely different in the case of cable glands used in explosion-hazard zones, which are used to introduce these cables into enclosures. In their case, an ATEX certificate is required, due to the fact that they influence the type of protection applied to the enclosure in which they are installed (e.g., Exd, Exe, or Ext).

The table below provides information on selecting the type of gland depending on the type of enclosure with which it is to be used.

X indicates permitted use.

Examples of cables for lighting installations in Ex zones

PUR cables are halogen-free, flame-resistant, and offer enhanced mechanical, chemical, and UV resistance – making them suitable for harsh environments. They can operate at temperatures ranging from -40°C to +125°C (however, always refer to the technical specifications provided by the manufacturer).

SY cable with a PVC outer sheath and braid. The braided armor, sometimes also referred to as a steel braid or mechanical protection, is particularly important for temporary applications where there is a higher risk of being crushed, stepped on, or run over. With a maximum ambient temperature of +70°C, this cable can be used in most industrial applications. However, it is less suitable for environments with low temperatures below +5°C, as the cable may become brittle.

H07RN-F cable is another option, often used in temporary lighting equipment in hazardous zones in Europe. It is a heavy-duty power cable with a durable rubber sheath, designed to be flexible and resistant to chemical, mechanical, and thermal stresses. It has a temperature range of -30°C to +60°C for fixed installations (up to +85°C for protected fixed installations) and from -15°C to +60°C when bent.