Plastic junction boxes can indeed be installed in attics, as both plastic and metal boxes are acceptable for use in these spaces. According to electrical experts, the key considerations when installing junction boxes in attics are ensuring they are accessible, properly mounted, and covered, rather than the material they are made from.
Metal vs Plastic Box Durability
Metal junction boxes are generally more durable than plastic ones, offering superior resistance to physical damage and environmental stresses. Metal boxes can withstand crushing impacts, extreme temperatures, and open flames without warping or melting. They are virtually impossible to bend, twist, or crush compared to plastic boxes. However, plastic junction boxes have their own durability advantages, including resistance to corrosion and moisture, making them suitable for damp environments. While both types can be appropriate depending on the application, metal boxes are typically preferred for harsh conditions or where maximum protection is required.
- Metal advantages: Fire-resistant, impact-resistant, crush-proof
- Plastic advantages: Corrosion-resistant, moisture-resistant, lightweight
- Choice depends on specific installation requirements and environmental factors
Grounding Requirements for Metal Boxes
Metal electrical boxes require proper grounding to ensure safety and comply with electrical codes. The National Electrical Code (NEC) mandates that all metal boxes and enclosures must be grounded or bonded. When using metal-sheathed cable or metal conduit, the metal box must be grounded through contact with the metal sheathing to complete the grounding circuit.
For installations using non-metallic (NM) cable in metal boxes:
- The bare copper or green grounding wire from the NM cable must be connected to the metal box using a grounding screw.
- All equipment grounding conductors of circuits spliced within the box must be connected to the metal box to ensure proper grounding for the largest potential fault.
- Grounding pigtails to both the box and the receptacle are typically required, though some argue that connecting only to a commercial-grade receptacle may be sufficient in certain cases.
It’s important to note that while plastic boxes do not require grounding themselves, they must still accommodate the proper connection of grounding conductors for the devices they contain.
Code Compliance for Attic Installations
Electrical junction boxes installed in attics must comply with specific National Electrical Code (NEC) requirements to ensure safety and accessibility. Key code compliance points for attic installations include:
- Junction boxes must be permanently accessible without removing any part of the building structure. This means they cannot be concealed under insulation or drywall.
- Boxes should be securely mounted to framing members or supported by approved methods.
- A minimum working space of 30 inches wide by 36 inches deep must be maintained in front of and around electrical equipment for safe operation and maintenance.
- Metal junction boxes must be properly grounded, while plastic boxes do not require grounding themselves but must accommodate grounding for devices.
- Wiring entering the box must be protected from abrasion and secured within 12 inches of the box.
It’s important to note that local codes may have additional requirements beyond the NEC. Always consult with a licensed electrician or local building department to ensure full compliance with all applicable codes for attic junction box installations.