Specifying IECEx Encoders for Hazardous Areas: Zones 1/21 vs. Zones 2/22

Short on Time? Send any questions through our contact page here, or call us directly on 1300 236 467

Understanding the Two Zone Groups

• Zones 1 & 21 (Normal Operation Risk): Explosive gas or combustible dust clouds are likely to occur during normal operations. Encoders here typically use flameproof (Ex db) and dust-ignition-proof (Ex tb) enclosures. Rather than merely preventing sparks, these heavy-walled housings act as pressure vessels. Precision-machined metal flamepaths along the shaft and joints cool escaping gases if an internal explosion occurs, preventing ignition of the surrounding atmosphere.
• Zones 2 & 22 (Abnormal/Fault Risk): Explosive atmospheres are not expected during normal operation and only occur briefly during an abnormal fault. Encoders here rely on non-sparking (Ex nA/Ex ec) electronics and dust-protected (Ex tc) enclosures, allowing for lighter, more compact housings.

Physical Composition & Material Standards

• Metallic housings and shafts: Zone 1/21 encoders generally use thick-walled 316L stainless steel, cast iron, or low-magnesium aluminium. In the case of underground coal mining (Group I), where the use of light metals is strictly prohibited to prevent thermite sparking, stainless steel is the only viable option. Zone 2/22 units are more likely to be anodised aluminium, coated steel or 303/316 stainless steel.
• Dynamic shaft seals: the rotating shaft is the natural path for leakage. Zone 21 requires IP6X (totally dust-tight) and Zone 22 requires IP54 or IP6X (again depending on whether the dust is conductive). The high-grade FKM (Viton) or PTFE shaft seals must pass thermal endurance ageing before ingress testing.
• Anti-static surfaces: the external paint and non-metallic parts must either have a coating thickness limited to less than 0.2mm (for Group IIC gases) or have a surface resistance of less than $10^9\ \Omega$ to prevent the generation of electrostatic brush discharges.

Permitted Encoder Technologies

• Magnetic encoders are the preferred choice in tough environments because they don't have the fragile glass discs that other encoder types do. Multi-turn energy-harvesting designs also eliminate the need for a backup battery inside hazardous areas.
• Optical encoders: Permitted when contained within a certified flameproof or non-sparking housing, for extremely high-resolution motion control.

Cabling & Communication Protocols

• Direct vs. Indirect Entry

  • Flameproof (Ex db) encoders require certified Ex d barrier glands (compound-filled) or factory-potted cables to maintain pressure containment. Zone 2/22 models use certified Ex e/Ex t glands that maintain IP ratings and cable pull-out resistance.

• Shielding & Earthing

  • Industrial Ethernet and fieldbus cables require continuous metallic shielding and proper equipotential bonding at the encoder housing to prevent stray currents and electromagnetic interference.

PCA IECEX Encoder Range

Need Help? Call Today!

Image