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:
- Personal Safety: Proper grounding ensures faults are quickly cleared by circuit
breakers or fuses, reducing the risk of electric shocks and fires.
- 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
- Lightning: Direct strikes, overhead discharges, or nearby strikes induce
dangerous currents and voltages in industrial systems.
- Switching Transients: Surge events caused by capacitor switching, fault clearing, or
network operations can impact equipment performance.
- Static Electricity: Rotating machinery and electrostatic charges on shafts can result
in damaging discharges if grounding is inadequate.
- 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:
- 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.
- 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.
- 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.
