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An Ex-suitable cable system is more than a cable
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Ex cable systems2026-08-086 min

An Ex-suitable cable system is more than a cable

In hazardous areas people often refer to an "Ex cable". It sounds logical: if the motor, terminal box and cable gland are Ex-certified, surely the cable itself must also be an ATEX cable.

Technically and legally, the answer is more nuanced. A power, control or instrumentation cable is usually a passive part of the installation, not a stand-alone item of Ex equipment with its own type of protection such as Ex d, Ex e, Ex i or Ex t. A commercial description such as "ATEX cable" does not prove that the cable can be used in every explosive-atmosphere installation without further assessment.

That does not make the cable less important. On the contrary, it is part of the overall protection concept. A wrongly selected cable can undermine the safe installation of otherwise correctly certified Ex equipment.

The cable must match the type of protection

The assessment starts with the connected Ex equipment and the installation context. Zone, Equipment Protection Level, gas or dust group, temperature class, type of protection and any special conditions in the certificate determine the requirements for the cable and cable entry. The real operating conditions then have to be considered: load current, short-circuit duty, ambient temperature, grouping, solar radiation, process heat, dust deposits, chemical exposure, vibration, movement, tensile load and mechanical damage.

The weakest limit in the system is decisive. If the equipment and cable gland can tolerate a higher temperature than the cable sheath, the sheath becomes the limiting factor. If oils, hydrocarbons, ammonia, solvents or cleaning agents attack the sheath, electrical insulation, dimensional stability, clamping and sealing can all be affected.

Explosion protection and ordinary electrical design cannot be separated. An undersized conductor, overloaded cable or poor termination can cause unacceptable temperatures even when the individual components carry Ex markings.

For Ex d, the outside is not enough

For flameproof equipment, the internal cable construction matters. A cable may look round, robust and sealed from the outside while having voids between the cores. Those voids may support gas migration and affect the behaviour of pressure and hot combustion products during an internal ignition.

For an Ex d application, the cable construction, cable gland, enclosure, gas group, certificate conditions and installation method must be considered together. Relevant factors include compactness, filling material, hygroscopic behaviour, sheath quality and whether a compression gland is sufficient or a compound-filled barrier gland is required.

The statement that Ex d always requires a barrier gland is too absolute. The opposite assumption, that every Ex d gland can be used with every cable, is equally wrong. The selection must be justified by manufacturer data, cable specification, certificate conditions and the applicable installation standard.

In intrinsic safety, the cable becomes part of the electrical system

In an intrinsically safe circuit, the cable is more than a mechanical connection. It adds capacitance and inductance to the circuit and therefore affects the available energy.

The system verification must show that the internal capacitance of the field device plus the cable capacitance does not exceed the permitted external capacitance of the associated apparatus: Ci + Cc <= Co. The same applies to inductance: Li + Lc <= Lo. The inductance-to-resistance ratio may also be limiting.

Permitted cable length is therefore not arbitrary. The lowest limit from capacitance, inductance or L/R ratio governs the design. A light-blue sheath does not make a circuit intrinsically safe; it mainly supports identification. Safety comes from entity parameters, cable data, segregation from non-intrinsically safe circuits, screening, earthing and system documentation.

The real cable diameter matters

For a cable gland, the nominal cable size is not enough. The actual outside diameter, roundness and sheath condition matter. A cable that is too small may not seal or grip properly. A cable that is too large may damage or distort the seal. An oval, ribbed or locally damaged sheath may fall outside the certified range of the gland.

Minimum bend radius also matters. A bend that is too tight can damage the cable internally, affect roundness or transfer mechanical stress to the gland. On vibrating machines, mobile equipment and dynamically loaded cables, a standard fixed-installation cable is not automatically suitable.

The verification file must provide the evidence

For the EU market, ATEX Directive 2014/34/EU governs equipment and protective systems placed on the market for use in potentially explosive atmospheres. Installation design and inspection are normally assessed through the relevant EN/IEC 60079 standards and national workplace-safety requirements.

For Great Britain, the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 2016 apply to products placed on the GB market. UKCA and CE marking rules must be considered in line with current UK government guidance. For Northern Ireland, the separate NI regime and EU/CE context remain relevant.

For a traceable Ex assessment, recording only a cable type and conductor size is not enough. The file should show why the cable is electrically, thermally, chemically and mechanically suitable. For Ex d, cable construction and gland selection must be justified. For intrinsically safe systems, capacitance, inductance, L/R ratio and maximum cable length must be documented.

This becomes critical during inspection and modification. A replacement cable may have the same conductor size but a different diameter, sheath material or internal construction. Electrically it may look equivalent; from an explosion-safety perspective it may need a different assessment.

Not the label, but the justification

The right question is not whether a "real Ex cable" can be bought. The right question is whether the selected cable is demonstrably suitable for the equipment, type of protection, environment and installation method.

A professional Ex installation is not created by placing individually marked components next to each other. It is created by designing and maintaining the interaction between cable, gland, enclosure, termination, earthing, mechanical protection, inspection and management of change.

Sources

Tags

#ATEX #UKCA #CE marking #IEC60079 #HazardousAreas #ExplosionSafety #CableSelection #Exd #IntrinsicSafety #DSEAR #AssetIntegrity #Inspection