Grounding & Bonding

Understanding the basics:

Key Definitions:

Grounding:
Connection to earth:
- Establishes reference to earth potential
- Lightning and surge dissipation
- Stabilizes voltage
- System grounding at source

Bonding:
Connection between conductive parts:
- Ensures same potential
- Provides fault current path
- Prevents shock from faults
- Equipment grounding conductor

Ground vs. Neutral:
- Neutral: Current-carrying conductor
- Ground: Safety conductor (no normal current)
- Connected at service entrance only
- Separate downstream

Why Grounding Matters:

Safety:
- Fault current operates protection
- Prevents shock from faulted equipment
- Limits touch voltage during faults
- Required by code (NEC Article 250)

Equipment Protection:
- Surge and lightning protection
- Static discharge control
- Noise reference for electronics
- EMI/RFI grounding

System Types:

Solidly Grounded:
- Neutral connected directly to ground
- Most common system
- Low voltage during ground faults
- Clear fault indication

Ungrounded:
- No intentional ground connection
- First ground fault doesn't trip
- Ground fault detection needed
- Legacy systems

High-Resistance Grounded:
- Limits ground fault current
- Production continues during fault
- Requires ground fault monitoring
- Good for continuous process

Impedance Grounded:
- Between solid and high-resistance
- Limits fault current
- Protects generators
- Special applications

Keeping equipment safe:

Equipment Grounding Conductor (EGC):

Purpose:
- Bond equipment to ground
- Carry fault current
- Operate overcurrent protection
- Maintain low impedance path

EGC Types:
- Copper wire (green or bare)
- Conduit (rigid, IMC, EMT)
- Cable armor (MC, AC)
- Wire in conduit (required for some)

Sizing:
- Based on overcurrent device rating
- NEC Table 250.122
- Increase for voltage drop on long runs
- Never smaller than required

Installation Requirements:
- Continuous from equipment to source
- Low impedance connections
- No fuses or disconnects in ground path
- Verify with continuity test

Bonding Equipment:

Bonding Methods:
- Bonding bushings at boxes
- Grounding locknuts
- Jumper wires around flexible sections
- Ground lugs and clamps

Bonding Conductors:
- Sized per NEC 250.102
- Based on service conductor size
- Maintain low impedance
- Copper preferred for connections

Common Bonding Needs:
- Metal raceways
- Equipment enclosures
- Structural steel
- Metal piping
- Fencing around equipment

VFD Grounding:

Special considerations:
- High-frequency currents
- Shielded motor cables
- 360-degree shield termination
- Dedicated ground conductor
- Minimize loop area

Implementing complete grounding systems:

Grounding Electrodes:

Types:
- Ground rods (copper-clad steel)
- Ufer ground (concrete-encased)
- Ground ring
- Metal underground water pipe
- Building steel

Requirements:
- 25 ohms or less (or two electrodes)
- Electrode bonded to system
- Protected from damage
- Accessible for testing

Installation:
- Minimum 8 ft depth for rods
- Proper soil contact
- Bonding of multiple electrodes
- Exothermic welds for connections

Grounding Electrode Conductor (GEC):

• Connects service to electrode
• Sized per NEC 250.66
• Continuous or spliced per code
• Protected from physical damage
• Copper or aluminum

Separately Derived Systems:

Definition:
Power source with no direct connection to supply (transformers, generators):
- Needs own grounding electrode conductor
- Bond neutral to ground at source
- Common in industrial systems

Transformer Grounding:
- Ground neutral at transformer
- Bond to building electrode system
- Or install separate electrode
- Coordinate with system type

Power Quality Grounding:

Isolated Ground:
- Orange receptacles
- Insulated ground conductor
- Reduces noise for electronics
- Still bonded at panel

Ground Grid:
- Low-impedance ground plane
- Computer rooms, control areas
- Equipment on same reference
- Bonded to building ground

Testing and career applications:

Testing Methods:

Ground Resistance:
- Fall-of-potential method
- Three-point testing
- Clamp-on ground testers
- Document results

Typical Values:
- Commercial: 25 ohms or less
- Industrial: 5-10 ohms
- Sensitive equipment: 1-5 ohms
- Telecom: <5 ohms

Continuity Testing:
- EGC continuity
- Bonding verification
- Low-ohm measurement
- Document all connections

Visual Inspection:
- Connection integrity
- Corrosion
- Proper installation
- Labeling

Common Problems:

Poor Connections:
- Loose lugs
- Corrosion
- Improper terminations
- Broken conductors

Missing Grounds:
- Unbonded equipment
- Broken conduit runs
- Removed ground wires
- Modifications without grounding

Ground Loops:
- Multiple ground paths
- Interference in signals
- Especially with communication cables
- Single-point ground for sensitive systems

Career Opportunities:

Electrician:
All electricians must understand grounding:
- Installation
- Troubleshooting
- Code compliance
- $55,000-$85,000

Electrical Engineer:
Grounding system design:
- Calculations
- Ground studies
- Power quality
- $75,000-$115,000

Ground System Specialist:
Testing and consulting:
- Ground resistance testing
- System evaluation
- Lightning protection
- $65,000-$95,000

Skills Development:

Fundamentals:
- NEC Article 250
- Theory of grounding
- Testing methods
- Safety principles

Advanced:
- Ground studies
- Power quality analysis
- Lightning protection
- Sensitive equipment grounding

Certifications:
- Electrical license
- Lightning protection certification
- Specialized testing credentials

Grounding knowledge is essential for all electrical professionals.