Understanding NEC Article 335: Instrumentation Tray Cable (Type ITC)

Introduction

NEC Article 335 establishes the rules for the use, installation, and construction of Instrumentation Tray Cable (Type ITC). This cable type is specifically designed for instrumentation and control circuits operating at 150 volts or less and 5 amperes or less. With its enhanced mechanical and electrical properties, Type ITC is ideal for industrial environments where reliable, low-power signaling is critical.

Scope

This article covers the installation and construction of Type ITC cables for instrumentation and control circuits. It allows for alternate wiring methods in industrial establishments, provided that maintenance and supervision are performed by qualified personnel.

Key Features of Type ITC Cable

1. Voltage and Current Ratings:
   • Operates at a maximum of 150 volts.
   • Limited to 5 amperes for 20 AWG and larger conductors; 3 amperes for 22 AWG.
2. Conductor Specifications:
   • Conductors range from 22 AWG to 12 AWG and are made of copper or thermocouple alloy.
   • Insulated conductors are rated for 300 volts.
3. Construction:
   • Resistant to fire propagation and designed with sunlight- and moisture-resistant jackets.
   • May include smooth metallic sheath, corrugated metallic sheath, or interlocking tape armor.
4. Marking:
   • Marked according to NEC 310.8(A)(2)-(5) with voltage ratings omitted.

Permitted and Prohibited Uses

Permitted Uses:

1. Installed in cable trays, raceways, or as aerial cable on a messenger.
2. Directly buried, if identified for the application.
3. Used under raised floors in industrial process control and IT equipment rooms.
4. In hazardous locations as permitted under NEC Articles 501.10, 502.10, 503.10, 504.20, 504.30, 504.80, and 505.15.
5. Installed without metallic sheaths or armor in areas where the cable meets the crush and impact requirements of Type MC cable and is identified as ITC-ER.

Prohibited Uses:

1. Circuits exceeding 150 volts or 5 amperes.
2. Installed with power, lighting, or non-power-limited circuits unless separated by insulating barriers.
3. Exposed installations not meeting impact resistance requirements.

Installation Requirements

1. Securing and Supporting:
   • Cables must be secured every 6 feet and mechanically supported when transitioning between cable trays or utilization equipment.
2. Bending:
   • Bends must be made carefully to avoid damaging the cable, adhering to the manufacturer’s guidelines.
3. Fire Resistance:
   • Type ITC cable must pass flame tests such as UL 1685-2010 or CSA C22.2 No. 0.3-M-2001 for fire propagation and smoke release.
4. Metallic Armor and Sheaths:
   • Optional metallic coverings provide additional mechanical and environmental protection. Continuous support is required for armored cables.

Applications

1. Industrial Instrumentation:
   • Used for process control systems, signal transmission, and monitoring in industrial facilities.
2. Hazardous Locations:
   • Suitable for installations in environments with flammable gases, vapors, or dust when properly armored or protected.
3. Data Centers and IT Rooms:
   • Installed under raised floors to support sensitive equipment.

Compliance and Best Practices

1. Follow Voltage and Current Limits:
   • Ensure all circuits remain within the 150-volt and 5-ampere limits to comply with NEC requirements.
2. Use Approved Materials:
   • Install only cables and fittings listed for Type ITC applications.
3. Routine Inspections:
   • Inspect for physical damage, proper support, and compliance with environmental conditions.

Conclusion

NEC Article 335 provides clear guidelines for the use and installation of Instrumentation Tray Cable (Type ITC). By adhering to these rules, electricians and engineers can ensure safe and reliable operation of control and instrumentation circuits in industrial environments.