NEC Article 240 outlines the requirements for overcurrent protection of electrical conductors and equipment. This ensures electrical systems are safeguarded against overcurrent conditions, preventing potential damage and hazards. Here is a comprehensive overview of NEC Article 240, covering sections 240.1 to 240.101:
240.1 Scope
This section establishes the scope of Article 240, including requirements for overcurrent protection devices such as fuses and circuit breakers, and their installation.
240.2 Definitions
Provides definitions for key terms used in Article 240 to ensure clarity and consistency. This includes terms like “overcurrent,” “overload,” “short circuit,” and “ground-fault.”
240.3 Other Articles for Specific-Purpose Overcurrent Protection
References other NEC articles that provide additional requirements for specific types of overcurrent protection, such as motor circuits (Article 430), transformers (Article 450), and hazardous locations (Article 500).
240.4 Protection of Conductors
- 240.4(A) Overcurrent Protection Devices: Specifies that conductors must be protected by overcurrent devices rated at or below their ampacity.
- 240.4(B) Devices Rated 800 Amperes or Less: Guidelines for protecting conductors with devices rated 800 amperes or less.
- 240.4(C) Devices Rated Over 800 Amperes: Guidelines for protecting conductors with devices rated over 800 amperes.
- 240.4(D) Small Conductors: Restrictions and conditions for small conductor protection.
240.5 Protection of Flexible Cords, Flexible Cables, and Fixture Wires
Specifies overcurrent protection requirements for flexible cords, flexible cables, and fixture wires to prevent damage and ensure safety.
240.6 Standard Ampere Ratings
Lists the standard ampere ratings for fuses and circuit breakers, ensuring they are properly matched to the conductor ampacity and load requirements.
240.7 Overcurrent Devices Rated Over 800 Amperes
Guidelines for selecting and installing overcurrent devices rated over 800 amperes.
240.8 Fuses or Circuit Breakers in Parallel
Prohibits the use of fuses or circuit breakers in parallel to protect the same conductor, ensuring overcurrent protection devices operate as intended.
240.9 Thermal Devices
Specifies that thermal devices used for overcurrent protection must comply with NEC requirements to ensure safety and reliability.
240.10 Supplementary Overcurrent Protection
Guidelines for using supplementary overcurrent protection devices that are not intended to provide primary protection for conductors.
240.12 Electrical System Coordination
Requires the coordination of overcurrent protection devices to ensure that only the device closest to the fault opens, minimizing the impact on the rest of the electrical system.
240.15 Ungrounded Conductors
Specifies the requirements for overcurrent protection of ungrounded conductors to prevent damage and ensure safety.
240.20 Grounded Conductors
Provides guidelines for overcurrent protection of grounded conductors, ensuring they are protected from overloads and short circuits.
240.21 Location in Circuit
Specifies location requirements for overcurrent protection devices within the circuit to ensure proper operation and protection:
- 240.21(A) Branch-Circuit Conductors: Location requirements for branch-circuit overcurrent protection.
- 240.21(B) Feeder Taps: Guidelines for overcurrent protection of feeder taps.
- 240.21(C) Transformer Secondary Conductors: Requirements for protecting transformer secondary conductors.
- 240.21(D) Service Conductors: Overcurrent protection requirements for service conductors.
240.22 Ground-Fault Protection of Equipment
Requires ground-fault protection for equipment to prevent damage from ground faults and ensure safety.
240.23 Change in Size of Ungrounded Conductor
Specifies requirements when there is a change in the size of an ungrounded conductor to ensure continued protection.
240.24 Location in or on Premises
Specifies installation requirements for overcurrent protection devices within a building or structure to ensure accessibility and safety.
240.33 Vertical Position
Requires overcurrent protection devices to be mounted in a vertical position unless they are designed and listed for horizontal mounting to ensure proper operation.
240.40 Disconnecting Means for Fuses
Specifies requirements for providing a disconnecting means for fuses to facilitate safe maintenance and replacement.
240.50 Classifications
Lists classifications for fuses and circuit breakers, providing guidelines for their proper selection and use.
240.51 Enclosures for Overcurrent Protection Devices
Specifies requirements for enclosures used to protect overcurrent protection devices, ensuring they are adequately protected from environmental factors.
240.52 Circuit Breakers with Integral Ground-Fault Protection
Guidelines for using circuit breakers that include integral ground-fault protection to enhance safety.
240.60 Nonrenewable Fuses
Outlines requirements for nonrenewable fuses, ensuring they provide adequate protection and are properly installed.
240.61 Use of Nonrenewable Fuses in Overcurrent Protection
Specifies conditions under which nonrenewable fuses can be used in overcurrent protection.
240.62 Use of Renewable Fuses
Guidelines for using renewable fuses in overcurrent protection applications.
240.63 Cartridge Fuses
Specifies requirements for cartridge fuses, ensuring they are used correctly and provide adequate protection.
240.64 Fuseholders
Specifies requirements for fuseholders to ensure compatibility with the fuses used and adequate protection.
240.65 Semiconductor Fuses
Guidelines for using semiconductor fuses, which are designed to protect semiconductor devices from overcurrent conditions.
240.66 Current-Limiting Fuses
Provides guidelines for using current-limiting fuses, designed to interrupt short circuits quickly and limit the energy let through to protected conductors and equipment.
240.80 Circuit Breaker as Overcurrent Protection Device
Specifies requirements for using circuit breakers as overcurrent protection devices, ensuring they are properly rated and installed.
240.81 Indicating
Requires circuit breakers to include an indicator to show whether the circuit is open or closed, facilitating safe operation and maintenance.
240.83 Marking
Requires circuit breakers to be clearly marked with their rating and other important information to ensure proper identification and use.
240.85 Applications
Provides guidelines for the appropriate applications of circuit breakers to ensure they are used correctly and provide adequate protection.
240.87 Arc Energy Reduction
Specifies requirements for reducing arc energy in circuits protected by circuit breakers to enhance safety and prevent damage from arc flash events.
240.88 Series Rated Combination Systems
Provides guidelines for the use of series-rated combination systems to ensure coordination and protection of the electrical system.
240.90 General
Outlines general requirements for overcurrent protection devices to ensure they provide adequate protection and operate reliably.
240.91 Location
Specifies location requirements for overcurrent protection devices within a circuit to ensure proper protection and safety.
240.92 Service Conductors
Provides guidelines for overcurrent protection of service conductors to ensure they are protected from overcurrent conditions.
240.93 Marking of Overcurrent Protection Devices
Requires overcurrent protection devices to be clearly marked with their rating and other important information to ensure proper identification and use.
240.94 Performance Testing
Specifies requirements for performance testing of overcurrent protection devices to ensure they operate reliably and provide adequate protection.
240.95 Ground-Fault Protection of Equipment
Requires ground-fault protection for equipment to prevent damage from ground faults and enhance safety.
240.100 Special Equipment for Hazardous Locations
Specifies additional requirements for overcurrent protection devices used in hazardous locations to ensure safety and compliance with relevant codes.
240.101 Protection of Conductors
Provides specific guidelines for protecting conductors in various installations, ensuring they are adequately safeguarded against overcurrent conditions.
Conclusion
NEC Article 240 provides detailed guidelines for installing and using overcurrent protection devices, ensuring electrical systems are protected from overcurrent conditions. These requirements prevent damage, overheating, and potential fire hazards, maintaining the integrity and safety of electrical installations.
For detailed information and further context, referring to the NEC Handbook and other resources provided by the NFPA is highly recommended.