Understanding NEC Article 320: Armored Cable Type AC

Introduction

NEC Article 320 provides comprehensive guidelines for the installation, use, and construction of armored cable (Type AC). Type AC cable is a widely used wiring method in residential, commercial, and industrial settings due to its flexibility, durability, and protective features. This article addresses critical aspects such as permitted uses, construction specifications, installation requirements, and safety considerations for Type AC cable, ensuring that installations meet safety and compliance standards.

Scope and Purpose

Article 320 covers the use, installation, and construction of Type AC cable, focusing on systems operating at 600 volts or less. It distinguishes Type AC cable from similar wiring methods, such as metal-clad (MC) cable, based on specific construction features and applications.

Key features of Type AC cable include:

• An outer metal armor for mechanical protection.
• A 16 AWG aluminum bonding strip for grounding.
• Insulated conductors with paper wrapping for added insulation and protection.

Permitted and Prohibited Uses

Uses Permitted:

Type AC cable may be used for:

1. Feeder and Branch Circuits: In both exposed and concealed installations.
2. Dry Locations: Ideal for environments free from moisture.
3. Cable Trays: Approved for use in cable tray systems.
4. Plaster or Masonry Walls: Embedded in plaster finishes on brick or masonry in dry locations.
5. Air Voids in Masonry: Allowed in air voids of masonry blocks or tile walls, provided these walls are not subject to excessive moisture.

Uses Not Permitted:

Type AC cable is prohibited in:

1. Damp or Wet Locations: The cable’s design is unsuitable for moisture-prone environments.
2. Exposed to Corrosive Conditions: Avoid use in areas with significant chemical or environmental corrosion risks.
3. Physical Damage: Must not be installed where mechanical damage is likely.
4. Masonry in Wet Locations: Cannot be embedded in plaster finishes on masonry subject to dampness.

Installation Requirements

1. Securing and Supporting:
   • Cables must be secured within 12 inches of junction boxes, cabinets, or fittings.
   • Supports are required at intervals not exceeding 4.5 feet.
   • Inaccessible spaces, such as attics, may have modified support requirements.
2. Bending Radius:
   • Bends in Type AC cable must maintain a minimum radius of five times the cable diameter to prevent damage.
3. Exposed Work:
   • Exposed runs of cable must closely follow building surfaces and be supported by running boards or similar methods to prevent physical damage.
4. Grounding:
   • Type AC cable includes an aluminum or copper bonding strip in contact with the armor for grounding. This design enhances safety by providing a fault current path without requiring additional grounding wires.

Construction and Material Standards

1. Flexible Metal Tape Armor:
   • The outer armor provides mechanical protection and serves as an equipment grounding conductor (EGC).
2. Moisture and Fire Resistance:
   • Conductors are insulated with a fibrous covering for moisture and fire resistance.
3. Marking and Identification:
   • Cables must have visible markings along their length to identify the manufacturer and ensure traceability.

Applications

1. Residential Wiring:
   • Commonly used for branch circuits in homes, providing flexibility and durability for concealed installations.
2. Commercial Settings:
   • Suitable for dry environments like offices and retail spaces where mechanical protection is essential.
3. Industrial Applications:
   • Used in cable trays or protected runs for equipment requiring reliable power delivery.

Compliance and Safety Tips

1. Material Selection:
   • Use cables specifically marked and listed for the intended application to ensure safety and compliance.
2. Proper Sealing:
   • Seal openings where cables enter enclosures to prevent abrasion or damage to conductors.
3. Regular Inspections:
   • Periodically inspect cable runs for wear, damage, or exposure to unsuitable conditions.
4. Use Anti-Short Bushings:
   • Install bushings at cable terminations to prevent damage to insulation and reduce short-circuit risks.

Conclusion

NEC Article 320 provides essential guidelines for the safe and effective use of Type AC cable. By adhering to its requirements, electricians and engineers can ensure compliance with safety standards, enhance system reliability, and meet the specific demands of residential, commercial, and industrial installations.