Understanding NEC Article 604: Manufactured Wiring Systems
NEC Article 604 provides standards for manufactured wiring systems, which are preassembled, factory-manufactured subassemblies used in field-installed electrical circuits. These systems streamline installation and improve safety, making them a preferred choice for accessible and dry locations, as well as specific applications like air-handling spaces.
Scope of Article 604
This article applies to:
- Branch circuits, remote-control circuits, signaling circuits, and communication circuits.
- Preassembled wiring systems used in accessible spaces or where listed for ducts, plenums, or air-handling areas.
Key Definitions:
- Manufactured Wiring System: A factory-assembled system of conductors and connectors intended for specific wiring methods.
Key Requirements for Manufactured Wiring Systems
- Listing Requirements
- All manufactured wiring systems and components must be listed.
- Reference Standard: ANSI/UL 183, Standard for Manufactured Wiring Systems.
- Installation
- Systems must be secured and supported according to the specific cable or conduit article from NEC Chapter 3.
- Installation in ducts, plenums, or air-handling spaces is permitted if listed for such applications.
Uses Permitted and Not Permitted
- Permitted Uses
- In accessible and dry locations.
- In ducts, plenums, and other air-handling spaces if listed for such use.
- Assemblies can extend into hollow walls for termination at switches or outlets.
- Not Permitted
- Where restricted by the applicable article in NEC Chapter 3 for the wiring method used.
Construction Standards
- Cable, Conduit, and Tubing Types
- Cable: Type AC or MC, with 8–12 AWG conductors, or smaller conductors (18 AWG minimum) for luminaires or specific circuits.
- Conduit and Tubing: Includes flexible metal conduit (FMC), liquidtight flexible metal/nonmetallic conduit (LFMC/LFNC), or EMT with 8–12 AWG conductors.
- Flexible Cord: Must be visible, hard-usage, and no longer than 6 feet for specific transitions.
- Busways
- Plug-in busways are permitted, rated up to 600 volts, and must include an equipment ground.
- Prewired Raceway
- Surface-mounted raceways must be listed for the application, with conductors rated for 600 volts and 20 amperes.
Marking and Connectors
- Marking
- Each section of the system must indicate the type of cable, flexible cord, or conduit used.
- Connectors
- Must be uniquely polarized and locking type to prevent accidental contact with live parts.
- Connectors and receptacles must be part of a listed assembly for the specific system.
Applications
NEC Article 604 is essential for systems in:
- Commercial Buildings: Modular setups for lighting and receptacles.
- Industrial Facilities: Prewired assemblies for machinery and controls.
- Air-Handling Spaces: Wiring within ducts and plenums where listed.
Conclusion
NEC Article 604 ensures safety and efficiency in the installation of manufactured wiring systems. By adhering to construction standards, listing requirements, and specific wiring methods, these systems provide reliable and streamlined electrical solutions.
