Instrument Earthing IEC Standards-Complete Guide for Industrial Systems
Instrument earthing is one of the most critical aspects of industrial electrical systems. Without proper earthing, sensitive instruments are exposed to noise, interference, and safety hazards. In industrial automation, control systems rely heavily on stable signals. If the grounding system is weak or poorly designed, measurement accuracy drops, interference increases, and even equipment failure can occur. This is where international standards like the IEC grounding standard come in.
Table of Contents
Table of Contents
IEC (International Electrotechnical Commission) has developed detailed guidelines that define how earthing should be designed, installed, and maintained. Following the instrument earthing IEC standard is not just about compliance. It is about ensuring long-term safety, system reliability, and consistent measurement performance. Industrial plants with critical process control systems benefit from these standards by minimizing downtime and avoiding costly equipment replacements.
Before exploring the technical details, it is important to understand why IEC standards matter. They provide globally recognized methods for designing earthing systems that protect both people and equipment. They also ensure that systems in different countries can follow a unified approach, which is crucial for global industries. Whether you work in oil and gas, power generation, manufacturing, or chemical processing, adhering to IEC earthing requirements is an investment in system integrity.
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Key Takeaways:
- IEC standards define how instrument earthing should be designed, tested, and maintained for industrial safety and performance.
- Proper earthing improves signal stability, reduces noise, and ensures compliance with EMC and safety regulations.
- IEC 60364, IEC 61010, IEC 61000, IEC 61557, and IEC 60079 are the main standards relevant to instrumentation grounding.
What is Instrument Earthing?
Instrument earthing is the process of connecting the non-current carrying parts of instrumentation equipment to the earth. This is done using conductors and grounding electrodes to create a low-resistance path for fault currents and unwanted electrical noise. From the IEC perspective, earthing is not just a protective measure; it is also a functional requirement for ensuring measurement accuracy and EMC (Electromagnetic Compatibility) compliance.
IEC 60364 earthing guidelines define how electrical systems, including instrumentation circuits, should be bonded and grounded to ensure safety and performance. In instrumentation systems, there are often separate grounding arrangements for protective earthing (safety) and functional earthing (signal reference). The IEC grounding standard emphasizes that both must be properly designed to prevent interference between power circuits and sensitive instrumentation.
Purpose & Benefits of Proper Earthing
Proper instrument earthing serves three main purposes: safety, noise reduction, and compliance. From a safety perspective, protective earthing ensures that exposed conductive parts remain at earth potential, reducing the risk of electric shock. From a noise perspective, a well-designed earthing system minimizes the effects of electromagnetic interference (EMI) and radio-frequency interference (RFI).
This is essential in process industries where sensors and control systems rely on accurate signal transmission. From a compliance perspective, IEC earthing requirements are part of global EMC regulations, meaning that your system must be grounded according to standards to meet certification and legal requirements. The benefits include increased equipment lifespan, reduced maintenance costs, fewer false alarms, and better process control accuracy.
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Relevant IEC Standards & Clauses
Several IEC standards cover earthing for instrumentation.
- IEC 60364 – Electrical installations of buildings. Part 5-54 deals with earthing arrangements, protective conductors, and equipotential bonding.
- IEC 61010 – Safety requirements for electrical equipment for measurement, control, and laboratory use.
- IEC 61000 – Electromagnetic compatibility requirements and testing.
- IEC 61557 – Testing, measuring, and monitoring of protective measures in low-voltage systems, including earth resistance testing.
- IEC 60079 – Electrical apparatus for explosive gas atmospheres, including grounding in hazardous areas.
These standards together form the complete framework for instrument earthing. Each provides specific technical details, from conductor sizing to permissible earth resistance values. Check our guide in detail on IEC earthing standard to know more about key clauses.
Types of Earthing in Instrumentation
IEC earthing requirements recognize different grounding strategies depending on the system’s needs. Single-point earthing connects all equipment grounds to a single location, ideal for reducing ground loops in sensitive measurement systems. Multi-point earthing bonds equipment at multiple points, useful for high-frequency noise control in large installations. Functional earthing provides a stable reference for instrument signals and is not primarily for safety.
Protective earthing ensures that conductive parts that might become energized are connected to earth to prevent shock hazards. The IEC grounding standard specifies when each type should be used, considering factors like cable length, system topology, and interference levels.
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Design Requirements per IEC
Designing an earthing system according to the instrument earthing IEC standard involves selecting the right conductor size, material, and layout. Copper is the most common material due to its low resistivity. IEC 60364 specifies minimum conductor sizes depending on mechanical strength and fault current levels. The layout must ensure the shortest possible path to earth to reduce impedance.
Separation between instrument earthing conductors and power earthing conductors is often required to prevent noise coupling. In hazardous areas, IEC 60079 specifies additional bonding and corrosion protection measures. Earth resistance should be low enough to safely dissipate fault currents—typically less than 1 ohm for sensitive instrumentation.
Installation Guidelines
IEC standards provide practical installation guidance to ensure compliance. Instrument earthing conductors should be run in dedicated conduits or trays separate from power cables. Bonding connections must be mechanically secure, corrosion-resistant, and accessible for inspection. Earthing pits should be located in areas where soil moisture is stable to maintain consistent earth resistance.
All metallic enclosures, cable shields, and racks should be bonded to the instrument earth. Shielded cables should be earthed at one end only in single-point systems to avoid ground loops. In multi-point systems, both ends may be earthed to improve high-frequency shielding.
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Testing & Maintenance per IEC 61557
IEC 61557 defines the methods for testing earthing systems. Earth resistance testing should be carried out during commissioning and periodically afterward. The fall-of-potential method is the most common. Insulation resistance testing ensures that earthing conductors are not degraded. Ground loop impedance testing can reveal hidden faults in bonding connections.
Regular inspection and cleaning of earth pits help maintain low resistance. Maintenance should also include checking for corrosion, loose connections, and accidental disconnections. All test results should be recorded and compared against IEC earthing requirements.
Why instrument earthing is Necessary?
Understanding the impact of electricity on the human body is critical for ensuring safety in electrical systems. The effects of electric current vary depending on its intensity and the path it takes through the body.
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Electricity and the Human Body
Human limbs possess a resistance of approximately 500 ohms, while the central torso offers a much lower resistance due to its high water content. When electricity penetrates the skin, it behaves somewhat like a Zener diode, with a reverse breakdown voltage typically ranging from 5 to 10 volts. This variation is influenced by individual skin characteristics and whether the skin is dry or greasy.
In the realm of electrical safety, health experts have established certain thresholds. A current as low as 1 milliampere (mA) is often cited as the threshold of sensation. At around 5 mA, an electric shock is described as “disturbing,” causing surprise in the recipient and even potential harm in certain circumstances. Currents in the range of 6-30 mA can lead to temporary paralysis, explaining why individuals often cannot release conductors during a shock.
More severe consequences occur with higher currents. In the range of 1 to 5 amperes (A), ventricular fibrillation can occur, leading to an inefficient pumping of blood by the heart. When a current of 10 A flows through the heart, it can lead to cardiac arrest.
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Dangerous Voltage Limit For The Human Body
In practical terms, the likelihood of high-current density flowing through the heart increases when the left hand and right foot serve as the connection points. Hand-to-hand connections can also be fatal.
When we consider the body’s resistance in an electrical circuit and aim to ensure safety, it’s generally recommended that a maximum voltage of approximately 24 volts should be encountered by humans. This is based on the worst-case scenario where a mild shock is permissible with a current of 4 mA.
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The preference for 24 V supplies for instrument systems is therefore understandable, as they allow working on low-voltage equipment without significant safety concerns. In practice, most people do not feel any sensation below about 40 V.
Although 110 V AC configured as 55-0-55 with the secondary center tapped to earth is common in the United States, it hasn’t been universally adopted due to the popularity of 220/240 V equipment elsewhere.
However, it’s crucial to note that even in low-voltage systems, heat generated at high currents can cause burns, so caution must always be exercised. To maintain safety under normal and fault conditions in a plant, the return path’s resistance should be low enough to prevent voltages exceeding 25 V peak.
IS (Instrument System) earth specification
As for Intrinsically Safe (IS) systems, standards like IEC 60079-14 require specific earth connections. The IS earth should be linked back to the earth reference using at least 4 mm2 copper cable with a resistance of less than 12 ohms. This earth should remain separate from other earth systems and must be identified as an IS earth.
A common practice in IS earth installation is using a pair of 10 mm2 cables, which have extremely low resistance over a 100 m run. While the method of identification isn’t standardized, one suggestion is to wrap the cable pair with turns of blue insulating tape every half meter for clarity.
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IS earth testing
Furthermore, testing IS Earth using twin parallel conductors is becoming the industry norm. By connecting the IS earth to the earth reference using two conductors, loop integrity can be easily checked by breaking one conductor and measuring or monitoring the loop resistance. This strategy also adds redundancy and lowers overall resistance, enhancing system integrity.
Connecting IS earth from different cabinets may involve looping through, but each interconnecting branch should be verified for integrity. The furthest branch must still meet the requirement of connecting back to the earth reference with a resistance of less than 1 ohm.
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500 V isolation test
For circuit isolation, the ability to withstand a 500 Vrms test for an IS circuit conductor has become internationally accepted as a fundamental requirement. IS circuit conductors in a cable must be isolated from Earth and other IS circuits to withstand this test for 1 minute.
In cases where this requirement cannot be met, certain countries’ codes of practice may require special approaches to address the issue. These approaches are detailed further in the application section, where accepted techniques for this scenario are discussed.
IEC 60079-0 Compliance: In environments where explosive gas atmospheres are a concern, adherence to IEC 60079-0 is imperative. This standard establishes general requirements for electrical apparatus and is crucial for instrument earthing in hazardous locations.
IEC 61010-1 and Safety: IEC 61010-1 addresses the safety of electrical equipment and covers grounding and insulation requirements for instruments. Compliance with this standard is crucial, particularly in laboratory, control, and measurement applications.
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IEC 60092-507 for Ships: When dealing with instrumentation on ships, following IEC 60092-507 is essential. This standard outlines electrical installation requirements, including proper earthing, to ensure safe maritime operations.
Low Voltage Equipment: IEC 60947-1 is indispensable for those working with low-voltage switchgear and control. It provides guidelines for the earthing and bonding of electrical equipment to ensure safe operation.
IEC 60364-4-41 and Electric Shock Protection: IEC 60364-4-41 focuses on protection against electric shock in low-voltage electrical installations. It underscores the significance of adequate earthing in safeguarding against electric shock.
Comprehensive Guidelines: These IEC standards offer comprehensive guidelines that encompass the selection of grounding materials, connections, and maintenance procedures.
Interference Mitigation: Proper instrument earthing following IEC standards reduces electromagnetic interference. This is crucial in applications where precise measurements and data integrity are paramount.
Grounding Systems: IEC standards specify the use of grounding systems, including grounding electrodes, conductors, and bonding methods, to establish a low-resistance path for fault currents.
Risk Mitigation: Compliance with IEC standards helps mitigate risks associated with electrical faults and lightning strikes by providing precise grounding techniques.
Ongoing Updates: It’s essential to recognize that IEC standards are subject to revisions and updates to align with technological advancements and evolving safety requirements. Staying informed about the latest revisions is crucial.
Common Mistakes and How to Avoid Them
Some of the most common mistakes in instrument earthing include mixing power and instrument earths without proper separation, failing to bond cable shields correctly, and using undersized conductors. Another mistake is not considering soil resistivity when designing earthing systems.
Ignoring maintenance can also lead to high resistance over time. To avoid these issues, always follow IEC grounding standard guidelines, use quality materials, and conduct regular testing. Proper documentation of the earthing layout and testing results is essential for ongoing compliance.
Conclusion
Following the instrument earthing IEC standard is not just a regulatory requirement—it is a critical part of industrial system design. By grounding instruments correctly, you protect equipment, improve measurement accuracy, and ensure safety for personnel. The IEC earthing requirements provide a complete framework, from design and installation to testing and maintenance.
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