A Practical Guide to Safe and Effective Grounding in Industrial Electrical and Automation Systems

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Grounding is a cornerstone of safety and performance in industrial electrical and electronic systems. Not only does it protect personnel by ensuring safe voltage levels on exposed metal surfaces, but it also safeguards sensitive electronic equipment from electrical disturbances like transients and surges. This guide covers everything you need to know about safe grounding in industrial plants, including key threats, terminologies, and grounding systems.

Why Grounding Is Essential

Grounding is vital for two primary reasons:

1. Personal Safety: Proper grounding ensures faults are quickly cleared by circuit breakers or fuses, reducing the risk of electric shocks and fires.
2. Equipment Protection: Electronic devices, especially solid-state components, are highly sensitive to transient electrical disturbances. A robust grounding system prevents damage from lightning, switching transients, static electricity, and other electrical anomalies.

Key Threats to Safe Grounding

1. Lightning: Direct strikes, overhead discharges, or nearby strikes induce dangerous currents and voltages in industrial systems.
2. Switching Transients: Surge events caused by capacitor switching, fault clearing, or network operations can impact equipment performance.
3. Static Electricity: Rotating machinery and electrostatic charges on shafts can result in damaging discharges if grounding is inadequate.
4. Electrical Fast Transients: Nearby arcing contacts or collapsing magnetic fields in coils cause voltage spikes that disrupt sensitive equipment.

Essential Grounding Terminologies

Understanding key grounding terms is vital to designing and maintaining an effective grounding system:

1. Ground (Earth)

The reference point in an electrical circuit for measuring voltages, providing a common return path for currents, or creating a direct connection to the Earth. Grounding ensures all voltages and currents remain stable and safe.

2. Ground Bus

A heavy copper bar where grounding wires terminate. The ground bus is connected to the plant's 0V reference point and routes grounding conductors to different subsystems.

3. Dirty Ground

Ground buses that handle high electrical currents from heavy machinery, like those in motor control centers (MCCs). These grounds can experience surges from motor startups, switching operations, and fault conditions.

4. Clean Ground

Ground buses isolated from heavy electrical loads. Clean grounds are used for sensitive electronics, ensuring they remain free from electrical noise and interference.

5. I.S. Ground (Intrinsic Safe Ground)

A single-point ground used for systems interfacing with hazardous areas. This grounding system minimizes the risk of sparking or overheating in explosive environments.

6. N-E Ground (Neutral-to-Earth Ground)

The point where the transformer neutral is connected to the plant’s 0V ground grid. This is the primary ground connection for the facility's electrical supply.

7. MCC Ground (Motor Control Center Ground)

The ground bus in MCCs handles high voltages and currents. It is subject to voltage spikes from motor startups and relay operations.

8. Instrument System Ground

A ground bus for instrumentation requiring clean and stable grounding, typically connected to the 0V plant ground via a dedicated conductor.

9. Lighting CC (Control Center)

A ground bus used for lighting systems, separately connected to the plant’s 0V ground reference.

10. PLC System Ground

A dedicated ground bus for Programmable Logic Controllers (PLCs) and similar devices, often linked to clean instrumentation buses for reliability.

11. SE Bar (Structural Earth Bar)

The bonding system that connects the building's structural frame directly to the 0V ground point.

Types of Grounding in Industrial Plants

Industrial plants typically use three primary types of grounding systems:

1. Dirty Grounds: Dirty ground inside a facility are typically 120VAC, 220VAC or 480VAC power grounds that are associated with high-current loads, such as MCCs. These grounds handle electrical noise, spikes, and surges.
2. Clean Grounds: Clean grounds are the DC grounds usually 24V DC reserved for instrumentation, metering/control systems, and communication networks to ensure stable and noise-free operation.
3. Structural Grounds: The interconnected ground system that ties the plant structure to the 0V reference point, creating a unified grounding system for safety and lightning protection.

Star Point Grounding: The Ideal Approach

A star point grounding system connects all subsystems—instrumentation, control systems, communication networks, and AC power—to a single grounding point. This prevents ground loops and ensures consistent voltage references across the facility. Key considerations for star point grounding include:

• Short and Direct Connections: Minimize conductor length to reduce resistance and voltage potential differences.
• Single Ground Path Per Subsystem: Avoid multiple ground paths to prevent errors caused by differing resistances.
• Periodic Inspection: Regularly check for corrosion, loose connections, and wear to maintain grounding integrity.

Safe grounding is essential for protecting personnel and equipment in industrial plants. By understanding grounding threats, using proper terminology, and implementing a star point grounding system, you can create a safe, efficient, and reliable grounding network. Maintaining separate dirty and clean grounds, along with a robust structural grounding system, ensures smooth operation of electrical and electronic systems. 

Understanding Grounding and Bonding: A Practical Guide for Safe Electrical Installations

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Proper grounding and bonding are fundamental to the safety and functionality of any electrical system. Whether you’re a homeowner, an electrician, or an engineer, understanding the principles of grounding and bonding can help ensure that electrical systems are not only efficient but also safe from potential hazards like electrical shocks and fires.

In the US, grounding and bonding are regulated by the National Electrical Code (NEC), while in the UK and Europe, they are guided by standards issued by the International Electrotechnical Commission (IEC) and national regulations such as BS 7671 (IET Wiring Regulations). This post will explore key concepts of grounding and bonding, explain why they are essential, and provide actionable tips for proper implementation.

What is Grounding (Earthing)?

In North America, grounding refers to connecting electrical systems to the earth. In the UK and Europe, the equivalent term is earthing. Earthing or grounding provides a safe path for fault currents to dissipate, preventing electrical shocks and fires.

Purpose of Grounding (Earthing)

1. Safety: Grounding/earthing prevents electrical shock hazards by directing excess current safely into        the ground.

2. Equipment Protection: Proper grounding safeguards appliances and systems from damage due to          overvoltage, lightning strikes, or faults.

3. Voltage Stabilization: It helps maintain consistent voltage levels across an electrical system by               providing a common reference point.

Types of Earthing Systems in Europe and North America

In Europe (IEC 60364 and BS 7671) we have:

1. TN System: The neutral is directly connected to earth, and exposed conductive parts are connected         to the neutral.

2. TT System: The exposed conductive parts are connected to earth electrodes that are independent of        the supply system.

3. IT System: The neutral is either not connected to earth or connected through a high impedance.

In the US (NEC): Grounding systems typically involve grounding the neutral conductor at the service entrance, with specific rules on grounding electrodes and grounding electrode conductors.

What is Bonding?

Bonding is the practice of connecting all metallic, conductive parts of an electrical system to ensure they have the same electrical potential. This minimizes the risk of electric shock by preventing voltage differences.

Purpose of Bonding

1. Shock Prevention: By equalizing the potential between conductive parts, bonding reduces the                likelihood of electric shocks.

2. Fire Prevention: Proper bonding minimizes the risk of arcing and fire due to potential differences.

3. Compliance with Standards: Both the NEC and IEC/BS 7671 require proper bonding to ensure            electrical safety.

Key Differences Between Grounding (Earthing) and Bonding

	Grounding (Earthing)	Bonding
Purpose	Provides a path to earth for fault current	Equalizes potential between conductive parts
Main Function	Safety during faults and surges	Prevents voltage differences
Connection	To the earth	Between conductive parts

Steps for Proper Grounding (Earthing) and Bonding

1. Install Grounding/Earthing Electrodes

Grounding/earthing electrodes, such as ground rods or plates, should be installed to provide a low-          resistance path to earth.

2. Connect the Grounding Electrode Conductor (GEC)

In North America, the GEC connects the service panel’s ground bus to the grounding electrode, as per NEC requirements. In Europe, the earthing conductor connects the distribution board’s earth bar to the earthing electrode, following IEC/BS 7671 guidelines.

3. Bond Metal Components

Bond all metallic components, such as water pipes, gas lines, and structural steel, to the ground/earth bar to equalize potential.

4. Use Approved Clamps and Connectors

Always use NEC- or IEC-compliant clamps and connectors for grounding and bonding connections. Loose or improper connections can cause dangerous faults.

5. Test the Grounding/Earthing System

Once installed, test the system to ensure it has a low resistance path to ground. Use a ground resistance tester for accurate results.

Common Mistakes to Avoid

1. Skipping Bonding of Metal Parts

Failing to bond all conductive parts can result in dangerous voltage differences and increase the risk of electric shock and fire.

2. Improper Sizing of Grounding/Earthing Conductors

Using undersized conductors can lead to overheating and system failure. Always follow NEC or IEC/BS 7671 guidelines for conductor sizing.

3. Not Testing the Grounding/Earthing System

Failure to test the system can result in undetected faults. Regular testing ensures that the system remains effective.

Compliance with Electrical Standards

NEC, IEC 60364, and BS 7671 Requirements

Both NEC and IEC/BS 7671 provide detailed guidelines on grounding (earthing) and bonding. Key sections include:

• NEC Article 250: Covers grounding and bonding requirements for electrical installations in North America.
• IEC Section 411: Covers protective earthing and automatic disconnection of supply.
• BS 7671 Section 542: Details earthing arrangements and earthing conductors.
• BS 7671 Section 543: Specifies protective bonding conductors.

Local Regulations

Always check local regulations, as they may have additional requirements specific to your region.

Understanding and properly implementing grounding (earthing) and bonding is essential for creating safe and reliable electrical systems. By following best practices and adhering to NEC, IEC, and BS 7671 standards, you can minimize the risk of electrical hazards and ensure long-term system performance.

If you’re unsure about any aspect of grounding or bonding, consult a licensed electrician or refer to the relevant national electrical code.

How a Residual Current Device (RCD) Works

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RCD means Residual Current Device. They are so called because they work based on the residual current in a circuit. The RCD is an electrical safety device specifically designed to immediately switch the electrical current flow when current "leaking" to earth is detected at a level harmful to a person using electrical equipment. An RCD offers a high level of personal protection from electric shock.

RCDs also help to reduce the risk of fire by detecting electrical leakage to earth in electrical wiring and accessories. RCDs are designed to operate within 10 to 50 milliseconds and to disconnect the electricity supply when they sense harmful leakage, typically 30mA

RCD Operating Principle

In absence of an earth fault,

Types of Earthing Systems Used in Electrical Installations

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The international standard IEC60364, part 4, and Reference 10 uses a set of diagrams to explain the five basic methods of earthing and providing the neutral of an electrical installation where it is required. The five methods are abbreviated TNC, TNS, TNCS, TT and IT.

The first letter denotes the source of power from a star-connected winding. T denotes that the star point of the source is solidly connected to earth, which is usually at a location very near to the winding.
I denote that the star point and the winding are isolated from earth. The star point is usually connected to an inductive impedance or resistance. Capacitive impedance is never used.

The second letter denotes the consumer. The consuming equipment needs

How to Measure Soil Resistivity

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Wenner’s four-electrode method is popularly used to measure soil resistivity. In this method Four electrodes are driven into the earth along a straight line at equal intervals, S. The depth of the electrodes in the ground is always of the order of 10 to 15 cm. The earth megger is placed on a steady and approximately level base. The four electrodes are connected to the earth megger terminal as shown below:

Soil Resistivity Values for Different Types of Soil

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One key determinant of a good earthing installation is the soil resistivity of the soil where the earth electrode is installed. If you are involved  in earthing buildings and electrical installations, here is a list of the typical soil resistivity values for different types of soil that you might encounter:

How to Use Earthing Rods for Earthing Improvement

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Vertically driven conductors called Earthing Rods are commonly used in earthing existing buildings and for improving or reducing electrical resistance of existing earth electrodes. See common terms used in earthing to gain understanding of earthing rod and earth electrode.

Characteristics of Earthing Rods
The rods used for earthing buildings may be:
(a) Copper or more commonly Copper clad steel. Copper clad steel are generally 1 or 2 meters long and provided with screwed ends and sockets in order to reach
considerable depths, if

Common Terms Used in Earthing/Grounding of Installations- Standard Practice

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Earthing or Grounding of electrical installation is a common practice. However, some common terms used in the practice could sometimes be tricky. Here, we have attempted to provide explanations for some of the more common terms used when earthing or grounding an installation. These terms are the ones used in the various national and international standards:

Earthing an Electrical Installation

To understand some of these terms, the schematic above will be very helpful:

Earthing Protection systems 1: common terms used

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Exposed conductive part

Any accessible metal parts of electrical equipment item other than the live parts
and which can accidentally become live.

Electrical fault

Accidental connection between two points at different potentials, such as
insulation fault.

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Fault voltage

Voltage, in case of an insulation fault, across an exposed conductive part and
an earthing reference.

Direct contact

Contact of persons with the normally live parts of electrical equipment

Non direct contact

Contact of persons with exposed conductive parts accidentally live due to an
insulation fault.

Double insulation

Insulation including both:
• Basic insulation required for protection against direct contact, and
• Supplementary insulation required for protection against indirect contact in case   of a fault of the basic insulation.