How many wires can fit in an electrical box?

It depends on box volume and wire gauge. A standard single-gang plastic box (18 cu in) can typically hold up to 9 wire connections (14-gauge) per NEC box fill calculations.

When do I need a metal electrical box?

Metal boxes are required when using metal conduit, in commercial buildings, and in some jurisdictions for all applications. They must be grounded.

Electrical Junction Boxes

Electrical

Boxes

$0.50-$10 per box

Electrical Junction Boxes (2026)

Prepared by Lumberama's Building Materials Team

|Last updated May 15, 2026|Sources & methodology

Electrical junction boxes house wire connections, outlets, and switches while protecting them from damage and containing potential sparks. Available in single-gang and multi-gang plastic for residential use, and metal boxes for commercial applications. Every wire connection in your home must be made inside an approved box.

Key Features

UL listed for safety
Multiple size configurations
Integral nail or bracket mounting
Cubic-inch volume ratings
Knockouts for cable entry

Specifications

Materials: PVC plastic

galvanized steel | Sizes: Single-gang (18 cu in)

double-gang (32 cu in)

4-square (21 cu in) | Mounting: Nail-on

bracket

old-work clips | Depth: 2-3/4 to 3-1/2 inches

Applications

Outlet locations
Switch locations
Junction points
Ceiling fixtures
Outdoor installations

Installation Overview

For new construction, nail or screw boxes to studs at the correct height (outlets at 12 inches, switches at 48 inches). For remodels, use old-work boxes with swing clips that grip drywall. Ensure proper box fill calculations.

Pros & Cons

Pros

✓ Inexpensive
✓ Required by code for all connections
✓ Easy to install
✓ Wide variety of sizes and types

Cons

✗ Must calculate box fill correctly
✗ Plastic boxes cannot be used with metal conduit
✗ Old-work boxes less secure than new-work
✗ Boxes must remain accessible

Top Brands

Southwire

Eaton

Code Requirements

NEC Article 314 requires all wire connections be made inside approved boxes. Box fill calculations per NEC 314.16 must not be exceeded. Boxes must remain accessible.

Buying Tips

Buy boxes in bulk for new construction to save significantly. Use old-work boxes for remodels where you cannot access studs. Always check box fill calculations before purchasing.