Grounding requirement for installation

Electrical Installations: A Comprehensive Guide

In electrical installations, grounding (also referred to as earthing) is a critical aspect that ensures the safety and functionality of equipment while preventing electrical hazards. Proper grounding protects both the equipment and personnel from electrical faults, such as current leaks or surges.

To ensure safety and compliance, grounding must adhere to current best practices (CBA) and guidelines from reputable standards like IEEE, NEC, or NFPA 99. Always consult your local electrical codes and standards for specifics.

This post provides a detailed guide to grounding requirements for electrical installations, offering practical insights from industry experience.

Why is Proper Grounding Essential?

1. Protect Equipment and Personnel: Good grounding ensures safe dissipation of fault currents and prevents hazardous situations like electric shocks.
2. Stabilize Voltage: Proper grounding stabilizes voltage levels during normal operations and surges.
3. Facilitate Safety Devices: Enables effective operation of safety devices like residual current devices (RCDs) or ground fault circuit interrupters (GFCIs).

Key Grounding Requirements

1. Grounding for 24 VDC Systems:
   • Ground the negative terminal of the power supply unless using an internally grounded power supply or a floating system (subject to Electrical Engineer approval).
2. Control Transformer Grounding:
   • Ground the common (neutral) terminal of the control transformer secondary to the control panel or enclosure.
3. Dedicated Ground for Instrumentation:
   • No separate earth stakes are needed for instrumentation/computer systems. A dedicated earth wire connected to the power supply earth can be used for “clean” grounding as required by vendors.
4. Grounding Electrical Components:
   • Ground all devices, machinery, metal enclosures, doors, support structures, and steel frameworks to a common earth ground point.
5. Cable Grounding:
   • All ground wires must run inside conduits or be integral to the cable.
6. Minimum Ground Conductor Size:
   • Provide a minimum 1.25 mm² (or #14 AWG) grounding conductor for each cable, either as a separate conductor or integral to the cable, installed in conduits or trunk systems.
7. Verification of Impedance:
   • Use an impedance measuring device to ensure that the resistance between touchable grounded points and the main ground is less than 0.1 ohms. Perform this test by injecting 10 amps into the circuit from a safe electrical low voltage (SELV) source.
8. Bolted Ground Connections:
   • Use compression-type ring lugs with non-corrosive hardware and lock washers. Conduits or wireways should never replace a dedicated ground connection.

Primary PE Ground Connections: Key Practices

• Use of Star Washers:
  • Apply toothed star washers for safety bonding under ring lugs or similar devices. Ensure ring lugs are double crimped for reliability.
• Fasteners and Termination:
  • Use locking fasteners, preferably with integral washers, to secure connections. Only one ground wire is permitted per grounding terminal.
• Material and Coating:
  • Use steel star washers. Non-conductive coatings (e.g., paint or anodizing) must be removed around the star washer area to ensure conductivity.
• Conductor Sizing:
  • The primary PE ground wire must be the same size or larger than the voltage-carrying wires. Branch circuits can use reduced wire sizes if capable of handling maximum fault current.
• Daisy-Chaining and Labeling:
  • PE ground wires may be daisy-chained, but the primary ground connection should have a single dedicated conductor to the main chassis or sub-panel. All main incoming ground connections must be labeled with the PE ground symbol.

Conclusion

Proper grounding is a cornerstone of any electrical installation, ensuring safety, equipment longevity, and compliance with standards. By following the outlined grounding requirements and best practices, you can achieve a safe and reliable electrical system.

For specialized scenarios or further details, always consult your local electrical guidelines and engage certified electrical professionals.