Lecture on NEC Code: Grounding and Bonding

Introduction to NEC Code and Article 250

• NEC Code: National Electrical Code governs electrical installations.
• Article 250: Focuses on grounding and bonding.
• Common confusion and debates among engineers and electricians.

Grounding and Bonding in Practice

• Importance of grounding and bonding for transformers, bonding XO, and service points.
• There’s often confusion about where and when to ground and bond.
• Importance of practical application and hands-on experience.

Purpose of Grounding and Bonding

• Effective Ground Fault Path: Ensures a low impedance path to open protective devices during faults.
• Reducing Touch/Step Potentials: Keeps all electrical components at the same potential to prevent shock.

Grounding Transformers

• Single Phase Example: X2 leg connected to ground for safety and NEC requirements.
• Importance of single-point grounding to avoid circulating currents.

Definitions from the NEC

• Ground: The earth, a point of reference for grounding.
• Grounding Electrode: Object making electrical connection to earth (e.g., ground rod, structural steel).
• Grounding Electrode System: All grounding electrodes connected together.
• Grounding Conductor: Connects system neutral to grounding electrode.

Bonding and Jumpers

• Bonding: Ensures electrical continuity and conductivity.
• Bonding Jumpers: Conductor connections ensuring required electrical conductivity.
• Service Equipment: Where utility meets power distribution system.
  • Main Bonding Jumper: Connects grounded conductor and equipment grounding.

Transformers and Separately Derived Systems

• Separately Derived Systems: No direct connection to other electrical sources except by grounding.
• Delta Y Grounded Transformer: Establishes a new, isolated power source.
• Importance of Transfer Switch Type: Switching neutral requires four-pole transfer switch if bonded.

System Grounding Types

• Solidly Grounded Systems: Direct earth connection.
• Impedance/Resistive Grounded Systems: Ground connection through impedance.

Objectionable Currents

• Current on grounding path without a fault is objectionable and not permitted by NEC.
• Example: Motion sensor switches using ground for power.

Service Entrance vs Separately Derived Systems

• Service Entrance: Equipment fed from utility source, requires specific grounding.
• Separately Derived System: New source, often from transformers, requires new grounding scheme.

Power Quality Considerations

• Importance of Proper Grounding: For safety and equipment longevity.
• Isolated Grounds and Single Point Grounding: Must be managed to avoid electrical noise and NEC violations.

Transfer Switch Systems

• Only one neutral-to-ground connection should exist.
• Example system with generator and transfer switch.
• Importance of proper grounding and bonding to avoid circulating currents and ensure safety.