Understanding NEC Article 386: Surface Metal Raceways

Introduction

NEC Article 386 outlines the requirements for the installation and use of surface metal raceways, which are rigid enclosures designed to house and protect electrical conductors. These raceways are used in environments where a sleek and accessible wiring solution is needed, such as commercial buildings, offices, and workshops.

Scope

This article applies to the use, installation, and construction specifications for surface metal raceways and their fittings. These raceways offer a versatile solution for managing wiring on building surfaces, providing mechanical protection and ease of access for modifications.

Key Features of Surface Metal Raceways

1. Material and Design:
   • Constructed from metal to provide mechanical strength and environmental resistance.
   • Available in various sizes to accommodate different conductor capacities.
2. Accessibility:
   • Equipped with removable covers for easy access to conductors and fittings.
3. Versatility:
   • Can be installed in dry locations and used in specific hazardous or raised floor applications when permitted.

Permitted and Prohibited Uses

Permitted Uses:

1. Dry Locations:
   • Ideal for areas free from moisture.
2. Hazardous Locations:
   • Allowed in Class I, Division 2 hazardous areas per 501.10(B)(3).
3. Raised Floors:
   • Permitted under raised floors in compliance with 645.5(E)(2).
4. Wall and Floor Extensions:
   • Can pass through dry walls or floors if unbroken and accessible on both sides.

Prohibited Uses:

1. Physical Damage:
   • Not suitable in areas prone to severe physical damage unless specially approved.
2. High Voltage:
   • Prohibited for voltages exceeding 300 volts unless the metal thickness is at least 1.02 mm (0.040 in.).
3. Corrosive Environments:
   • Not permitted in areas with corrosive vapors.
4. Hoistways and Concealed Locations:
   • Prohibited unless explicitly permitted by NEC.

Installation Guidelines

1. Conductor Size and Capacity:
   • Conductors must not exceed the size for which the raceway is designed.
   • The total conductor cross-sectional area must not exceed 20% of the raceway’s interior cross-sectional area.
2. Securing and Supporting:
   • Raceways must be supported as per the manufacturer’s instructions, with secure attachments to prevent movement or damage.
3. Splices and Taps:
   • Splices and taps are allowed only in raceways with accessible removable covers. These must not occupy more than 75% of the raceway’s cross-sectional area at the splice or tap point.
4. Grounding:
   • The raceway must include provisions for connecting an equipment grounding conductor, especially when transitioning between different wiring methods.
5. Marking and Identification:
   • Each section must be clearly marked for identification and compliance with 110.21(A).
6. Combination Raceways:
   • When used for multiple systems (e.g., signaling and power), compartments must be clearly separated and identified by color coding, imprinting, or stamping.

Applications

1. Commercial Wiring:
   • Provides a clean, professional solution for managing wiring in offices and retail spaces.
2. Workshops and Laboratories:
   • Offers durable and accessible wiring pathways for tools and equipment.
3. Hazardous Environments:
   • When listed, can be safely used in specific hazardous locations.

Compliance Tips

1. Select Proper Raceways:
   • Ensure the raceway is listed and suitable for the intended location and application.
2. Maintain Accessibility:
   • All conductors, splices, and taps must remain accessible for maintenance and inspection.
3. Monitor Conductor Fill:
   • Avoid overfilling to maintain safety and compliance with NEC guidelines.

Conclusion

NEC Article 386 provides essential guidelines for the safe and effective use of surface metal raceways. By adhering to these rules, electricians and engineers can ensure reliable, compliant, and professional electrical installations.