Understanding NEC Article 366: Auxiliary Gutters

Introduction

NEC Article 366 provides guidelines for the use, installation, and construction of auxiliary gutters, which supplement wiring spaces in electrical enclosures or equipment. Auxiliary gutters are distinct from raceways like wireways and are used to provide additional space for wiring bending and deflection. This article ensures that these components are safely integrated into electrical systems while maintaining compliance with NEC standards.

Scope

This article applies to both metallic and nonmetallic auxiliary gutters, covering their permitted applications, restrictions, and construction requirements. Auxiliary gutters are used in various installations where additional wiring space is needed, such as for panelboards or terminal connections.

Key Features of Auxiliary Gutters

1. Material:
   • Available in sheet metal and nonmetallic forms, depending on application and environmental requirements.
   • Must meet construction standards for corrosion resistance and durability.
2. Purpose:
   • Provides extra space for conductors, enabling easier bending and termination.
   • Accommodates both bare and insulated busbars in certain installations.
3. Marking:
   • Nonmetallic gutters must be marked for sunlight resistance, wet locations, and insulation temperature ratings.

Permitted and Prohibited Uses

Permitted Uses:

1. Indoor and Outdoor Installations:
   • Sheet metal gutters are suitable for both indoor and outdoor environments.
   • Nonmetallic gutters are allowed outdoors if listed for sunlight resistance and wet locations.
2. Conductor Grouping:
   • Permitted to group feeders, branch circuits, and service conductors.
3. Extended Runs:
   • Allowed to extend up to 30 feet from equipment, with exceptions for elevator systems.

Prohibited Uses:

1. Equipment Housing:
   • Cannot enclose switches, overcurrent devices, or similar equipment.
2. Hazardous Locations:
   • Not suitable for hazardous or corrosive environments unless specifically listed.

Installation Guidelines

1. Securing and Supporting:
   • Sheet metal gutters must be secured every 5 feet.
   • Nonmetallic gutters require supports every 3 feet and at terminations.
2. Conductor Limits:
   • The sum of conductor cross-sectional areas cannot exceed 20% of the gutter’s interior cross-section.
3. Splices and Taps:
   • Allowed within gutters if accessible and not filling more than 75% of the space.
4. Grounding:
   • Metallic gutters must be bonded to equipment grounding conductors or jumpers.
5. Expansion Fittings:
   • Required when length changes exceed 0.25 inches due to temperature variations.

Applications

1. Supplementing Panelboards:
   • Auxiliary gutters are often used to extend wiring spaces for large panelboards.
2. Multi-Conductor Terminations:
   • Ideal for systems requiring numerous conductor terminations in compact spaces.
3. Commercial Buildings:
   • Widely used in buildings to organize and protect complex wiring systems.

Compliance Tips

1. Use Listed Products:
   • Ensure gutters and fittings are listed for the specific environment and application.
2. Monitor Fill Levels:
   • Adhere to the 20% fill limitation to avoid overheating and ensure safe operation.
3. Regular Inspections:
   • Periodically inspect gutters for damage, corrosion, or non-compliance issues.

Conclusion

NEC Article 366 offers essential standards for the effective use of auxiliary gutters in electrical systems. By providing additional space for wiring, these components help maintain safety, organization, and efficiency. Electricians and engineers can rely on these guidelines to ensure compliance and optimal system performance.