Metal vs PVC Electrical Boxes: Which Should You Use?

Choosing between metal and PVC (plastic) electrical boxes depends on your installation requirements, code requirements, and environmental conditions. Here's a comprehensive comparison.

Metal Electrical Boxes

Types of Metal Boxes

• Steel: Most common, galvanized for corrosion resistance
• Aluminum: Lightweight, good for outdoor use
• Cast iron/aluminum: Weatherproof applications

Advantages

• ✅ Provides excellent ground path (when properly bonded)
• ✅ Fire resistant
• ✅ Strong and durable
• ✅ Required for certain wiring methods (MC cable, EMT)
• ✅ Better EMI shielding
• ✅ Can be used in exposed locations

Disadvantages

• ❌ More expensive than PVC
• ❌ Can rust in wet locations (if not rated)
• ❌ Heavier and harder to work with
• ❌ Requires bonding for grounding
• ❌ Sharp edges can damage wire insulation

PVC (Plastic) Electrical Boxes

Types of PVC Boxes

• Standard PVC: General indoor use
• Old work (cut-in): Remodel applications
• Weatherproof PVC: Outdoor rated

Advantages

• ✅ Less expensive than metal
• ✅ Non-conductive (no bonding required)
• ✅ Won't rust or corrode
• ✅ Lightweight and easy to install
• ✅ No sharp edges
• ✅ Good for damp locations

Disadvantages

• ❌ Not fire resistant (can melt)
• ❌ Not as strong as metal
• ❌ Cannot be used with metal-clad cables (without adapter)
• ❌ Can crack in cold temperatures
• ❌ May not be allowed in commercial/industrial

Code Requirements

When Metal Boxes Are Required

• Metal conduit systems (EMT, IMC, RMC)
• MC cable installations (typically)
• Some commercial and industrial applications
• Where AHJ specifically requires

When PVC Boxes Are Acceptable

• NM cable (Romex) in residential
• UF cable installations
• PVC conduit systems
• Most residential applications

Box Fill Considerations

Both metal and PVC boxes follow the same NEC 314.16 fill requirements. The box type doesn't change your calculation—only the volume matters.

Making Your Choice

Choose Metal When:

• Using metal conduit or MC cable
• Fire resistance is a concern
• In exposed or accessible locations
• Commercial or industrial settings
• AHJ requires it

Choose PVC When:

• Using NM cable in residential
• Budget is a concern
• Working in damp or corrosive environments
• Doing remodel work (cut-in boxes)
• PVC conduit system

Related Resources

• All Box Types & Specifications
• Junction Box Sizing Guide
• Box Fill for Remodel Work

Calculate Fill for Any Box

Regardless of metal or PVC, use our box fill calculator to ensure your box meets NEC 314.16 requirements.