When designing rigid metal conduit (RMC) installations, selecting appropriate connectors and couplings is critical for code compliance, safety, and long-term performance. This guide breaks down the differences, applications, and selection criteria for threaded versus threadless fittings.

Understanding Rigid Conduit Fittings

Rigid conduit connectors and couplings join sections of galvanized steel or aluminum conduit or terminate runs into enclosures/panels. They serve three core functions:

1. Maintaining electrical continuity
2. Providing mechanical support
3. Protecting conductors from damage

Two primary types exist:

• Threaded Fittings: Require pre-cut threads on conduit ends
• Threadless Fittings: Secure to smooth conduit via set screws or compression mechanisms

Threaded Connectors & Couplings: The Industrial Standard

Applications

• Mandatory in NEC Class I Division 1 hazardous locations (flammable vapors/combustible dust)
• Heavy industrial facilities, chemical plants, and oil refineries
• Environments requiring extreme physical impact resistance

Key Advantages

• Superior vibration resistance
• Uncompromised grounding integrity
• Meets strict NEC 501.10(A)(1) hazardous area requirements

Technical Specifications

• Sizes: 1/2" to 6" (common: 1/2"–2")
• Installation Requirements:
  • Conduit threading equipment
  • Thread sealant for wet/corrosive environments

Threadless Fittings: Efficiency-Focused Solutions

Variants

• Set-Screw Type: Fast installation via clamping screws
• Compression Type: Watertight seal using compression ring + nut

Ideal Use Cases

• Commercial buildings, parking garages, data centers
• Surface-mounted exposed conduit runs
• Dry/damp locations (compression type for wet areas)

Performance Benefits

• 60% faster installation vs. threaded systems
• Clean aesthetics for architecturally exposed areas
• UL-listed wet location ratings (compression type)

Technical Notes

• Sizes: 1/2" to 4" (common: 1/2"–2")
• Restrictions: Set-screw types prohibited in wet locations

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