NEC 240.4-d

Small Conductor Protection - 240.4(D) Requirements

Complete code requirements, compliance guidance, and professional analysis

Code Requirements Summary

NEC 240.4(D) provides specific overcurrent protection requirements for small conductors (14, 12, and 10 AWG), establishing maximum overcurrent device ratings that may be smaller than the conductor's ampacity to ensure adequate protection.

Professional Requirements

  • Protect 14 AWG copper conductors with maximum 15-ampere overcurrent devices
  • Protect 12 AWG copper conductors with maximum 20-ampere overcurrent devices
  • Protect 10 AWG copper conductors with maximum 30-ampere overcurrent devices
  • Apply aluminum conductor protection rules when using aluminum conductors
  • Consider conductor ampacity limitations in addition to 240.4(D) requirements
  • Ensure overcurrent device ratings comply with both conductor protection and load requirements

Technical Explanation

NEC 240.4(D) recognizes that small conductors need special protection beyond their normal ampacity ratings. While 14 AWG copper has an ampacity of 20 amperes in many applications, 240.4(D) limits overcurrent protection to 15 amperes to provide additional safety margin. This accounts for factors like conductor heating, insulation degradation, and connection integrity at smaller wire sizes. The rule ensures that small conductors, which are more vulnerable to damage from overcurrent conditions, receive appropriate protection.

Industry Applications

Residential branch circuit design and overcurrent device selection
Commercial lighting circuit protection and conductor sizing
Small motor circuit protection and conductor selection
Control circuit design and overcurrent protection
Electrical panel specification and breaker sizing
Code compliance verification for small conductor installations

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Professional Resources

NEC 2023 State Adoption Status

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Related Code Requirements

NEC 240.4->
NEC 240.6->
NEC 310.15(B)(16)->

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