Understanding NEC Article 338: Service-Entrance Cable (Types SE and USE)

Introduction

NEC Article 338 governs the use, installation, and construction specifications for Service-Entrance (SE) and Underground Service-Entrance (USE) cables. These cables are crucial for safely delivering electricity to residential, commercial, and industrial facilities. Type SE cable is designed for aboveground use, while Type USE is optimized for underground installations, including direct burial.

Scope

This article applies to service-entrance cables used for connecting utility power to service equipment. It includes general installation rules, permitted and prohibited uses, and construction requirements.

Key Features of SE and USE Cables

1. Conductor Specifications:
   • Type SE: Includes conductors like RHW, RHW-2, XHHW, XHHW-2, THWN, and THWN-2.
   • Type USE: Equivalent to RHW or XHHW; USE-2 offers higher temperature ratings.
2. Voltage Ratings:
   • Rated for systems up to 600 volts.
3. Marking:
   • Identifies cable type, temperature ratings, and intended use.
4. Temperature Ratings:
   • SE: 75°C (if unmarked) or 90°C (if marked).
   • USE-2: Rated 90°C for wet or dry locations.

Permitted and Prohibited Uses

Permitted Uses:

1. Type SE Cable:
   • For aboveground service-entrance conductors.
   • Branch circuits and feeders in dry locations.
2. Type USE Cable:
   • For underground installations, including direct burial.
   • As service-entrance wiring when terminating in outdoor enclosures.

Prohibited Uses:

1. Type SE Cable:
   • Underground installations without additional protection.
   • Locations prone to physical damage without mechanical protection.
2. Type USE Cable:
   • Interior wiring.
   • Aboveground installations unless properly terminated and protected.

Installation Guidelines

1. Bending Radius:
   • Minimum radius of five times the cable diameter for curved installations.
2. Interior Installations (Type SE):
   • Ampacity adjustments for cables in contact with insulation must follow Table 310.15(C)(1).
3. Exterior Installations:
   • SE cables must be supported and comply with Article 225 for outdoor wiring.
4. Direct Burial (Type USE):
   • Must meet specific depth requirements and use cabled assemblies for multiple conductors.

Construction Requirements

1. Assemblies:
   • USE cables can be twisted (cabled) for direct burial applications.
   • SE cables require flame-retardant coverings for safety.
2. Grounding Conductors:
   • Bare or covered grounding conductors are allowed within Type SE cables.
3. Marking:
   • Cables must indicate temperature ratings and conductor sizes.

Applications

1. Residential Wiring:
   • SE cable is commonly used for aboveground service-entrance connections in homes.
2. Utility Connections:
   • USE cable facilitates underground service-entrance wiring for residential and commercial buildings.
3. Rural and Agricultural Facilities:
   • Provides durable solutions for remote power installations.

Compliance and Safety Tips

1. Protect from Damage:
   • Ensure cables are shielded from physical impacts and environmental factors.
2. Follow Temperature Limits:
   • Adhere to conductor and cable temperature ratings during installation.
3. Inspect Regularly:
   • Check for wear, insulation damage, or non-compliance with NEC standards.

Conclusion

NEC Article 338 provides critical guidelines for the safe and effective use of service-entrance cables. By adhering to these standards, electricians can ensure reliable power delivery and compliance with safety requirements. Whether used for aboveground or underground applications, SE and USE cables are indispensable in modern electrical systems.