What Is NEC Article 310?

NEC Article 310 covers the general requirements for conductors rated 2000 volts or less, including their types, insulation, construction, installation methods, and allowable uses. It applies to general building wiring as well as feeders, branch circuits, and conductors used in specialized applications referenced in other NEC sections.

Scope and Purpose

The article ensures that conductors are properly sized, insulated, and installed to prevent overheating, mechanical damage, or premature failure. It addresses conductor ampacity, temperature ratings, environmental conditions, and mechanical protection, helping installers choose the right conductor type for the intended location—whether dry, damp, wet, or corrosive environments.

Key Requirements

• Lists approved conductor types such as THHN, THWN, XHHW, RHH, USE, each with defined voltage, temperature, and environmental ratings.
• Specifies insulation materials and construction requirements for different applications.
• Requires compliance with ampacity tables (e.g., NEC Table 310.15(B)(16)) considering conductor size, insulation, ambient temperature, and number of conductors in a raceway or cable.
• Outlines installation methods, including in raceways, cable trays, direct burial, and concealed or exposed runs.
• Includes marking, identification, and color-coding rules for grounded, ungrounded, and equipment grounding conductors.
• Provides adjustments for ampacity when conductors are bundled or exposed to higher ambient temperatures.

Conclusion

NEC Article 310 is the primary reference for selecting and installing conductors in most electrical systems. For the wire and cable industry, it defines the parameters for conductor types, insulation ratings, and installation practices, ensuring that wiring meets both performance needs and NEC safety requirements.