NEC Article 250 covers the general requirements for grounding and bonding of electrical installations. Grounding and bonding are critical for the safe operation of electrical systems, preventing electrical shock, fires, and ensuring the proper operation of overcurrent protection devices. Here is a comprehensive overview of NEC Article 250, covering sections 250.1 to 250.197:

250.1 Scope

This section establishes the scope of Article 250, which includes requirements for grounding and bonding electrical systems, circuits, and equipment.

250.2 Definitions

Provides definitions for key terms used in Article 250 to ensure clarity and consistency. This includes terms like “grounding conductor,” “bonding conductor,” “ground-fault,” and “bonding jumper.”

250.4 General Requirements for Grounding and Bonding

Outlines the general principles for grounding and bonding, ensuring that electrical systems are safely grounded and bonded:

• 250.4(A) Grounding of Electrical Systems: Specifies requirements for grounding electrical systems to the earth.
• 250.4(B) Bonding of Electrical Systems: Details the requirements for bonding electrical systems to ensure electrical continuity and safety.

250.6 Objectionable Current over Grounding Conductors

Specifies measures to prevent objectionable current from flowing over grounding conductors, ensuring system safety and functionality.

250.8 Connection of Grounding and Bonding Equipment

Provides guidelines for the proper connection of grounding and bonding equipment to ensure secure and reliable connections:

• 250.8(A) Permitted Methods: Lists acceptable methods for connecting grounding and bonding equipment.
• 250.8(B) Methods Not Permitted: Specifies methods that are not allowed for making these connections.

250.10 Protection of Ground Clamps and Fittings

Requires that ground clamps and fittings be protected from physical damage to ensure they remain effective and safe.

250.12 Clean Surfaces

Specifies that contact surfaces for grounding connections must be clean and free from paint, enamel, or other non-conductive coatings to ensure a good electrical connection.

250.20 Alternating-Current Systems to Be Grounded

Details the types of alternating-current (AC) systems that must be grounded, including:

• 250.20(A) AC Systems of 50 Volts to 1000 Volts: Systems that must be grounded under certain conditions.
• 250.20(B) AC Systems of More Than 1000 Volts: Specifies grounding requirements for high-voltage AC systems.

250.21 Alternating-Current Systems Not Required to Be Grounded

Lists the types of AC systems that are not required to be grounded and the conditions under which they may operate.

250.22 Circuits Not to Be Grounded

Specifies circuits that should not be grounded to prevent interference with the intended operation of the system.

250.24 Grounding Service-Supplied Alternating-Current Systems

Provides detailed requirements for grounding service-supplied AC systems to ensure safety and compliance:

• 250.24(A) System Grounding Connections: Specifies the connections needed for system grounding.
• 250.24(B) Grounding Electrode Conductor: Requirements for the grounding electrode conductor used to connect the system to the grounding electrode.

250.28 Main Bonding Jumper and System Bonding Jumper

Specifies the requirements for the main bonding jumper and system bonding jumper, ensuring proper connection and system integrity.

250.30 Grounding Separately Derived Alternating-Current Systems

Details the grounding requirements for separately derived AC systems, such as transformers and generators, to ensure they are safely grounded and bonded.

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s)

Provides guidelines for grounding and bonding buildings or structures that are supplied by feeders or branch circuits from another building or structure.

250.34 Portable and Vehicle-Mounted Generators

Specifies grounding requirements for portable and vehicle-mounted generators to ensure safety and compliance.

250.50 Grounding Electrode System

Requires that a grounding electrode system be established for each building or structure to ensure proper grounding:

• 250.50(A) General: Lists acceptable grounding electrodes that can be used.
• 250.50(B) Electrodes: Provides guidelines for installing and connecting grounding electrodes.

250.52 Grounding Electrodes

Details the types of grounding electrodes that are permitted, such as metal underground water pipes, metal frame of the building, concrete-encased electrodes, and ground rings.

250.53 Grounding Electrode System Installation

Provides guidelines for the proper installation of grounding electrodes to ensure they are effective and safe.

250.56 Resistance of Rod, Pipe, and Plate Electrodes

Specifies the maximum resistance allowed for rod, pipe, and plate electrodes to ensure they provide adequate grounding.

250.64 Grounding Electrode Conductor Installation

Details the installation requirements for grounding electrode conductors, ensuring they are properly installed and protected:

• 250.64(A) General: Specifies installation requirements for grounding electrode conductors.
• 250.64(B) Sizing: Guidelines for sizing grounding electrode conductors.
• 250.64(C) Continuous: Requires that grounding electrode conductors be installed in one continuous length without splice or joint unless irreducible and securely joined.

250.66 Size of Alternating-Current Grounding Electrode Conductor

Provides guidelines for determining the size of the grounding electrode conductor for AC systems to ensure they are adequately sized for the intended load.

250.90 Bonding

Specifies the general requirements for bonding, ensuring that all conductive materials are effectively bonded to create an electrically continuous path.

250.92 Bonding of Services

Details the bonding requirements for electrical services to ensure they are properly bonded to the grounding system.

250.94 Bonding for Other Systems

Provides guidelines for bonding other systems, such as communications systems, to the electrical grounding system to prevent potential hazards.

250.96 Bonding Other Enclosures

Specifies the requirements for bonding other enclosures, such as raceways and cable trays, to the grounding system.

250.102 Bonding Jumpers

Provides detailed guidelines for installing bonding jumpers, ensuring they are properly sized and installed to maintain system integrity.

250.104 Bonding of Piping Systems and Exposed Structural Steel

Requires the bonding of piping systems and exposed structural steel to the grounding system to prevent potential hazards and ensure electrical continuity.

250.110 Equipment Fastened in Place or Connected by Permanent Wiring Methods (Fixed) – Grounding

Specifies the grounding requirements for fixed equipment to ensure safety and compliance.

250.112 Specific Equipment Fastened in Place or Connected by Permanent Wiring Methods

Details the grounding requirements for specific types of equipment, ensuring they are properly grounded for safety.

250.114 Equipment Connected by Cord and Plug

Specifies the grounding requirements for equipment connected by cord and plug to ensure they are properly grounded and safe to use.

250.119 Identification of Equipment Grounding Conductors

Requires that equipment grounding conductors be clearly identified by color or marking to ensure they are easily distinguishable from other conductors.

250.120 Equipment Grounding Conductor Installation

Provides guidelines for installing equipment grounding conductors, ensuring they are properly connected and protected.

250.122 Size of Equipment Grounding Conductors

Specifies the requirements for sizing equipment grounding conductors to ensure they are adequate for the intended load.

250.126 Identification of Wiring System Components Grounded to an Effective Ground-Fault Current Path

Requires clear identification of components that are grounded to an effective ground-fault current path to ensure proper maintenance and troubleshooting.

250.130 Equipment Grounding Conductor Connections

Details the requirements for connecting equipment grounding conductors to the grounding system to ensure effective grounding.

250.136 Equipment Grounding Conductor Connections at the Source of a Separately Derived System

Specifies the requirements for connecting equipment grounding conductors at the source of a separately derived system, such as a transformer or generator.

250.140 Frames of Ranges and Clothes Dryers

Provides guidelines for grounding the frames of electric ranges and clothes dryers to ensure safety.

250.148 Continuity and Attachment of Equipment Grounding Conductors to Boxes

Specifies the requirements for maintaining the continuity of equipment grounding conductors and their attachment to electrical boxes.

250.170 to 250.195 Reserved

These sections are reserved for future use and currently do not contain any specific requirements.

250.196 Effective Date

Specifies the effective date for the requirements outlined in Article 250, ensuring compliance with the latest standards.

250.197 Reference Standards

Provides a list of reference standards used in Article 250, ensuring consistency and compliance with industry practices.

Conclusion

NEC Article 250 provides comprehensive guidelines for grounding and bonding electrical systems, ensuring safety and compliance. These requirements help prevent electrical shock, fires, and ensure the proper operation of overcurrent protection devices by providing a reliable path to ground.

For detailed information and further context, referring to the NEC Handbook and other resources provided by the NFPA is highly recommended.