Cables in Hazardous Areas
Cables in Hazardous Areas
Cables might seem like a minor detail compared to the equipment they connect, but in hazardous areas they require careful consideration. A cable that's perfectly suitable in a normal environment might be completely inappropriate where explosive atmospheres could exist. EN/IEC 60079-14 establishes the requirements for cable selection and installation in classified zones, and getting cables wrong can undermine the protection of every piece of equipment they connect.
How Cables Become Ignition Sources
Cables can create ignition-capable conditions in several ways. Damaged insulation can cause short circuits with electrical arcing—a powerful ignition source. Overloaded cables generate heat that could ignite a surrounding explosive atmosphere or degrade nearby equipment. Physical damage from mechanical impact, abrasion, or chemical attack can expose live conductors. Even cable glands—the fittings where cables enter enclosures—can compromise explosion protection if incorrectly selected or installed, creating a weak point in an otherwise sound protection concept.
Cable Selection
Cables for hazardous areas must be suitable for both the electrical load and the environmental conditions. Key selection factors include:
- Temperature rating: The cable must be rated above the maximum operating temperature considering both ambient conditions and self-heating from current flow
- Chemical resistance: The sheath material must resist whatever chemicals are present—oils, solvents, acids, or cleaning agents that could degrade insulation
- Mechanical protection: Armoured cables provide protection against physical damage; where armour isn't used, external mechanical protection (conduit, trunking) may be needed
- Fire performance: Flame-retardant cables prevent fire propagation along cable routes—an important consideration when cables run through multiple zones
Cable Installation
How cables are installed matters as much as which cables you choose. Routes should avoid areas where mechanical damage is likely—away from traffic routes, moving equipment, and areas where maintenance activities could disturb them. Where damage risk is unavoidable, cables need additional protection. Cables shouldn't be routed where they could be exposed to temperatures exceeding their rating, or where they might be immersed in chemicals they're not resistant to.
Proper support and fixing prevents cables sagging, rubbing, or being strained at termination points. Cable routes should be planned to maintain segregation between different circuit types—particularly keeping intrinsically safe circuits separate from power cables.
Intrinsically Safe Circuit Cables
Cables carrying intrinsically safe circuits have requirements beyond normal hazardous area cables. Because intrinsic safety depends on limiting the energy that can reach the hazardous area, the cable parameters—capacitance and inductance per unit length—are part of the safety calculation. Using the wrong cable can increase stored energy beyond safe limits, invalidating the entire intrinsic safety concept.
IS cables must be physically segregated from non-IS cables to prevent energy transfer between circuits. Blue sheath colouring is conventionally used to identify intrinsically safe cables, making segregation visually verifiable during inspection. Cable parameters must be documented and available for verification against the IS circuit safety calculations.
Cable Glands
The cable gland is where the cable meets the enclosure, and it's a critical point for maintaining explosion protection. For flameproof enclosures, the gland must be certified to the same standard and maintain the flamepath concept—an incorrect gland creates an unprotected path for hot gases. For increased safety equipment, the gland must maintain the required IP rating against moisture and contaminant ingress.
Gland selection must match the cable type (armoured or unarmoured), the cable outer diameter (glands have specific ranges—a gland too large for the cable won't seal properly), the environment (corrosion, chemicals, temperature), and the protection concept of the equipment it's fitted to. Unused cable entries in enclosures must be properly sealed with certified blanking elements—never with tape, rags, or improvised stoppers.
Inspection of Cables and Glands
During inspection, cables and glands receive specific attention. Inspectors look for physical damage to cable sheaths, correct gland selection and installation, proper sealing of unused entries, evidence of overheating or discolouration, and correct identification marking. For intrinsically safe circuits, segregation from other cables is verified. A single loose gland or damaged cable can compromise an entire installation's integrity—which is why proper documentation of cable specifications and gland types is essential for ongoing maintenance.
