Understanding NEC Article 336: Power and Control Tray Cable (Type TC)

Introduction

NEC Article 336 governs the use, installation, and construction of Power and Control Tray Cable (Type TC). Designed for power, lighting, control, and signal circuits, Type TC cable offers flexibility and durability for industrial and commercial applications. It supports a range of configurations, including installations in cable trays, raceways, and direct burial, making it a versatile choice for modern wiring needs.

Scope

This article covers Type TC cable’s permissible uses, construction standards, and installation practices. It applies to tray cables used in industrial, commercial, and specific residential settings.

Key Features of Type TC Cable

1. Voltage and Current Ratings:
   • Supports circuits up to 600 volts.
   • Conductor sizes range from 18 AWG to 1000 kcmil for copper, nickel-coated copper, and aluminum.
2. Construction:
   • Nonmetallic, flame-retardant outer jacket.
   • May include metallic shielding or armor for added protection.
3. Marking:
   • Cables are marked “Type TC” and may include additional labels such as “TC-ER” for exposed runs and “TC-ER-HL” for hazardous locations.

Permitted and Prohibited Uses

Permitted Uses:

1. For power, lighting, control, and signal circuits.
2. In cable trays and raceways.
3. Direct burial when identified for the purpose.
4. Exposed runs (TC-ER) when protected against physical damage.
5. In outdoor installations supported by messenger wires.
6. For Class 1 and non-power-limited fire alarm circuits.
7. For hazardous locations when marked TC-ER-HL.

Prohibited Uses:

1. Where exposed to physical damage without protection.
2. In outdoor installations where not identified as sunlight resistant.
3. Outside of raceways or cable trays unless specifically permitted by other provisions.

Installation Requirements

1. Bending Radius:
   • Minimum radius depends on cable diameter:
     • 4 times the diameter for cables ≤ 1 inch.
     • 5-6 times the diameter for larger cables.
   • Metallic-shielded cables require a radius of at least 12 times the diameter.
2. Securing and Supporting:
   • Cables must be secured at intervals not exceeding 6 feet.
   • Exposed runs require mechanical protection like struts or channels.
3. Grounding:
   • Grounding conductors must be included within the cable or clearly identified during installation.

Applications

1. Industrial Systems:
   • Used for power distribution, control systems, and instrumentation in factories and plants.
2. Commercial Buildings:
   • Supports lighting and HVAC systems.
3. Hazardous Locations:
   • TC-ER-HL cables ensure safety in environments with flammable gases or dust.
4. Residential:
   • Limited to use in one- and two-family dwellings for branch circuits and feeders (TC-ER-JP).

Best Practices

1. Inspect Regularly:
   • Check installations for wear, damage, and compliance with NEC standards.
2. Use Approved Materials:
   • Ensure all cables and fittings are listed for their intended use.
3. Follow Local Codes:
   • Comply with additional requirements specific to the installation site.

Conclusion

NEC Article 336 provides clear guidelines for safely installing and using Type TC cables. By following these standards, electricians can ensure the longevity, reliability, and safety of electrical systems. Whether used in industrial, commercial, or specific residential applications, Type TC cable offers a robust solution for diverse wiring needs.