Understanding NEC Article 370: Cablebus

Introduction

NEC Article 370 establishes guidelines for the safe use, installation, and construction of cablebus systems. A cablebus consists of a metal framework housing insulated conductors that are supported at controlled intervals. It is a versatile and efficient method for high-capacity electrical power distribution in industrial and utility settings, offering advantages in terms of flexibility, durability, and safety.

Scope

This article covers the installation requirements for cablebus systems and associated fittings. Cablebus is designed for systems handling high currents and voltages, offering a reliable solution for feeders, branch circuits, and service entrances.

Key Features of Cablebus

1. Construction:
   • Metal frameworks with insulating blocks support continuous insulated conductors.
   • A ventilated top cover encloses the conductors, allowing free air circulation to enhance ampacity.
2. Conductor Requirements:
   • Minimum conductor size is 1/0 AWG.
   • Conductors must have insulation rated at 75°C or higher.
3. Marking:
   • Systems must include nameplates at termination points, specifying voltage, ampacity, and conductor details.

Permitted and Prohibited Uses

Permitted Uses:

1. Voltage and Current Applications:
   • Suitable for all voltage and current levels for which the conductors are rated.
2. Indoor and Outdoor Installations:
   • May be installed in dry, damp, wet, or corrosive environments when identified for these conditions.
3. Wall and Floor Penetrations:
   • Can pass through partitions, walls, and floors when compliant with fire and vapor barrier requirements.

Prohibited Uses:

1. Hazardous Locations:
   • Restricted unless explicitly permitted by other NEC sections.
2. Hoistways:
   • Not allowed due to safety risks.

Installation Guidelines

1. Securing and Supporting:
   • Framework must be supported at intervals not exceeding 12 feet.
   • Conductors require support every 3 feet horizontally and 1.5 feet vertically.
2. Overcurrent Protection:
   • Must be installed per 240.4, with exceptions for certain high-voltage installations.
3. Conductor Ampacity:
   • Free air tables in 310.17 and 315.60(C) determine ampacity.
   • Terminations must account for equipment temperature limits to avoid overheating.
4. Grounding and Bonding:
   • Framework can serve as an equipment grounding conductor when bonded according to 250.118(A)(12).

Applications

1. Industrial Facilities:
   • Ideal for high-current distribution to heavy machinery.
2. Power Utilities:
   • Used in substations and power plants for efficient power transfer.
3. Renewable Energy Systems:
   • Facilitates high-voltage connections in solar or wind installations.

Compliance Tips

1. Adhere to Manufacturer Instructions:
   • Use specified connectors and follow installation guidelines for terminations.
2. Monitor Conductor Spacing:
   • Ensure proper spacing and support to maintain system integrity.
3. Inspect and Maintain:
   • Conduct periodic inspections to prevent physical damage or degradation.

Conclusion

NEC Article 370 ensures the safe and efficient installation of cablebus systems in demanding environments. By adhering to these guidelines, electricians and engineers can optimize the performance of high-capacity electrical systems while ensuring safety and compliance.