Earthing in Hazardous Areas – IEC 60079 Guidelines
Earthing is one of the most critical safety practices in industrial environments. In hazardous areas, where explosive gases, vapors, or dust may be present, earthing becomes even more essential. The primary purpose of earthing in such locations is to prevent electrical sparks or static discharges that can ignite explosive atmospheres. The IEC 60079 standard provides comprehensive guidance on how to design, implement, and maintain earthing systems in these areas.
Table of Contents
Table of Contents
In industries like oil and gas, petrochemical plants, refineries, and chemical processing facilities, hazardous atmospheres are common. Improper grounding can lead to catastrophic explosions, equipment loss, and even fatalities. This is why understanding hazardous area earthing IEC requirements is not optional—it is mandatory for compliance and safety.
IEC 60079 sets the benchmark for protection methods in explosive environments. It covers everything from equipment selection to grounding strategies. Whether you are an electrical engineer, safety officer, or maintenance professional, mastering these guidelines will help you build a safer workplace.
Key Takeaways
- Hazardous area earthing IEC guidelines aim to eliminate ignition sources by controlling static and fault currents.
- IEC 60079 focuses on bonding, earthing, and material selection for explosive atmospheres.
- Proper design reduces risks of arc flashes, static discharges, and voltage potentials in hazardous zones.
- Bonding and earthing are not the same—bonding equalizes potential, while earthing connects to the ground.
- Using conductive materials and regular inspection ensures long-term compliance and safety.
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IEC 60079 Scope & Definitions
The IEC 60079 standard is a global benchmark for electrical installations in explosive atmospheres. It defines requirements for equipment and protective systems in hazardous locations.
A hazardous area is any location where flammable gases, vapors, or combustible dust can form an explosive mixture with air.
Hazardous Area Classifications
Hazardous areas are categorized based on the frequency and duration of the explosive atmosphere:
- Zone 0: Continuous presence of explosive gas (e.g., inside process vessels)
- Zone 1: Likely presence during normal operation (e.g., near pump seals)
- Zone 2: Presence only under abnormal conditions (e.g., around storage tanks)
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For dust:
- Zone 20: Explosive dust present continuously
- Zone 21: Present during normal operations
- Zone 22: Occurs rarely and for short duration
IEC 60079 also defines terms like equipotential bonding, earthing system, and static electricity control.
Earthing Requirements for Explosive Atmospheres
Purpose of Earthing in Hazardous Areas
The main goal of earthing in hazardous locations is to:
- Prevent ignition due to electrical faults or static discharge.
- Ensure that exposed conductive parts remain at earth potential.
- Provide a path for fault currents to flow safely to ground.
If equipment in hazardous zones is not properly grounded, even small potential differences can lead to sparks. These sparks can ignite flammable gases or dust clouds, causing an explosion.
IEC 60079 Earthing Principles
IEC 60079 recommends that:
- All metallic non-current-carrying parts must be connected to the earthing system.
- Earthing conductors should have low impedance and mechanical strength.
- Continuity of bonding should be verified regularly.
- Earthing points should be clearly marked and accessible for testing.
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Below is a comparison table of IEC 60079 earthing requirements for different hazardous zones:
| Zone | Earthing Requirement | Remarks |
|---|---|---|
| Zone 0 | Permanent bonding and low-resistance earthing | Equipment inside must be intrinsically safe |
| Zone 1 | Bond all conductive parts to earth | Redundant bonding recommended |
| Zone 2 | Bonding required but less stringent | Visual inspection often acceptable |
| Dust Zones | Conductive flooring and bonding to prevent static | Similar to gas zones |
Bonding & Static Control per IEC
Bonding and earthing are often confused, but IEC 60079 makes a clear distinction:
- Earthing: Connecting equipment to the earth to dissipate fault currents.
- Bonding: Connecting different conductive parts to ensure they have the same potential.
Why Static Control Matters
Static electricity is a hidden ignition source in hazardous areas. Activities like pouring liquids, transferring powders, or moving belts can generate static charges. IEC 60079 specifies measures to control static, such as:
- Bonding all metallic objects involved in transfer processes.
- Using anti-static hoses and conductive flooring.
- Keeping surface resistivity within safe limits (usually <10^8 ohms).
Example from IEC 60079: When filling a tank with flammable liquid, both the filling nozzle and tank must be bonded together before the transfer begins. This prevents a potential difference that could cause a spark.
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Special Materials & Methods
Material selection plays a major role in hazardous area earthing. IEC 60079 suggests the following:
- Use corrosion-resistant metals for earthing conductors (copper or galvanized steel).
- Avoid aluminum in wet or corrosive areas unless properly protected.
- Use non-sparking tools for installation and maintenance.
Earthing Conductor Sizing
The conductor size depends on the prospective fault current and mechanical strength required. As a rule:
- Minimum cross-sectional area for copper: 16 mm²
- For steel: 25 mm²
Table: Recommended Earthing Conductor Size
| Material | Minimum Size |
|---|---|
| Copper | 16 mm² |
| Aluminum | 25 mm² |
| Steel | 25 mm² |
Methods of Earthing
IEC 60079 permits different earthing methods:
- Direct Earth Connection: Each equipment connected individually.
- Ring Earth System: Common in refineries, providing redundancy.
- Grid Earthing: For large facilities with multiple hazardous zones.
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Inspection & Maintenance
Earthing in hazardous areas is not a one-time activity. IEC recommends:
- Visual inspection during every maintenance cycle.
- Resistance testing annually.
- Immediate correction of any broken bonding or corroded connections.
Connection to Instrument Earthing
Instrument grounding in hazardous zones follows similar safety principles. For detailed guidance, refer to instrument earthing IEC standard which provides insight on controlling interference and maintaining safety for sensitive devices.
Practical Design Considerations
- Use short and straight earthing conductors to reduce impedance.
- Avoid sharp bends as they increase inductance.
- Ensure all mechanical joints are secure and corrosion-free.
- Keep separate earthing systems for power and instrumentation where possible.
Conclusion
Hazardous area earthing IEC guidelines under IEC 60079 ensure that equipment and structures in explosive atmospheres remain safe. Earthing and bonding protect against static buildup and fault currents, reducing the risk of ignition. Choosing the right materials, following proper installation methods, and conducting regular inspections are essential steps for compliance and safety.
By applying these standards, industries can prevent accidents, protect assets, and safeguard lives. Always consult IEC 60079 and related standards when designing or maintaining hazardous area installations.
What is the NEC code for earthing?
The NEC code for earthing (grounding) is primarily covered under Article 250, which provides requirements for grounding and bonding of electrical systems for safety and fault protection.
What are the hazards of earthing?
Improper earthing can lead to electric shock, fire hazards, equipment damage, and overvoltage risks due to ineffective fault current dissipation.
What is the NFPA code for grounding?
The NFPA code for grounding is included in NFPA 70 (National Electrical Code), mainly in Article 250, specifying grounding and bonding standards for electrical installations.
What are the rules of earthing?
Key rules include connecting all exposed conductive parts to earth, maintaining low resistance paths, proper conductor sizing, and ensuring compliance with local standards like NEC or IEC.
What is article 250 of the NEC grounding?
Article 250 of the NEC outlines grounding and bonding requirements for electrical systems, covering conductor sizing, electrode systems, fault path integrity, and protection against voltage surges.
What are the basic earthing requirements?
Basic requirements include using an approved earth electrode, maintaining earth resistance within standard limits (e.g., ≤25 ohms for NEC), proper conductor sizing, and continuous grounding path integrity.
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