Understanding NEC Article 545: Manufactured Buildings and Relocatable Structures
NEC Article 545 provides electrical requirements for manufactured buildings and relocatable structures, focusing on the safe connection, wiring, and grounding of these facilities. These structures are commonly used as temporary offices, classrooms, or modular buildings.
Scope of Article 545
This article applies to:
- Manufactured Buildings: Factory-built structures transported to a site and installed on a permanent foundation.
- Relocatable Structures: Movable units designed for temporary use and connected to electrical supplies at various locations.
Exclusions:
- Manufactured homes, which are governed by Article 550.
Key Definitions:
- Manufactured Building: Not built on a chassis; designed for permanent installation.
- Relocatable Structure: Temporary, often modular, structures.
Key Requirements for Manufactured Buildings
- Wiring Methods
- All NEC-compliant wiring methods, including metal raceways and cables, are permitted.
- Closed construction allows cables to be secured only at cabinets, boxes, or fittings for conductors 10 AWG or smaller.
- Service Conductors and Equipment
- Service-entrance conductors must be installed after on-site erection unless the point of attachment is pre-determined.
- Service equipment must comply with Article 230 requirements.
- Grounding and Bonding
- Prewired panels must provide bonding for all exposed metal parts that could become energized, per Article 250.
- Grounding electrode conductors must connect the service to the grounding electrode.
- Component Interconnections
- Factory-fitted connectors used for module interconnections must withstand vibration and comply with applicable standards.
Key Requirements for Relocatable Structures
- Power Supply
- Structures must be powered by feeders, with conductors including an equipment grounding conductor.
- Multiple interconnected units may each have separate panelboards supplied by separate feeders.
- Disconnecting Means
- Each relocatable structure must have a readily accessible disconnecting means, such as a breaker or switch.
- Ground-Fault Circuit-Interrupters (GFCI)
- GFCI protection is mandatory for all receptacle outlets in compartments accessible from outside the structure.
- Bonding of Metal Parts
- All non-current-carrying metal parts likely to become energized must be bonded to the panelboard grounding terminal or enclosure.
- Intersystem Bonding
- A single communication system bonding termination can be used if all interconnected structures share a grounding conductor.
Applications
NEC Article 545 is crucial for:
- Modular Classrooms: Temporary or semi-permanent school facilities.
- Temporary Offices: On-site trailers for construction projects.
- Portable Buildings: Event structures or emergency shelters.
Conclusion
NEC Article 545 ensures the safety of electrical systems in manufactured buildings and relocatable structures through specific requirements for wiring, grounding, and equipment protection. By addressing the unique needs of these structures, the article supports their safe and reliable operation.
