Electrical Box Basics All Homeowners Should Know

May 2024 · 2 minute read

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Family Handyman

New work: 3 types do it all

If you have the walls opened up for remodeling or putting on an addition, these three boxes cover about 99 percent of your needs.

  • 22-CU.-IN. 4-IN. ROUND BOX for ceiling light fixtures, smoke alarms, carbon monoxide detectors and wall sconce light fixtures.
  • 22-CU.-IN. SINGLE-GANG BOX for a typical outlet or switch.
  • 32-CU.-IN. DOUBLE-GANG BOX for two light switches together in the same box, or two duplex receptacle outlets.

    • The purpose of electrical boxes

    Wiring connections—where wires join an outlet, switch or other wires—must be inside an electrical box. Here’s why: Connections are the weak link in an electrical system. If they get damaged, loosened or pulled apart, you’re left without power, or worse, with a fire. Electrical boxes are simply meant to protect vulnerable connections.

    Next, read: The 8 Most Common National Electric Code Violations DIYers Make.

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    Family Handyman

    Box material

    Indoor nonmetallic boxes are typically plastic or fiberglass. Cheap PVC boxes like the one shown at far right work fine, but they can move or distort in wood framing as the studs dry. I prefer to spend the extra 20¢ per box on heavy-duty thermoset plastic or fiberglass boxes. Unlike PVC boxes, they’re super strong and maintain their shape.

    Box Size

    Wires, receptacles and switches need adequate space. Crowded boxes can damage wires, resulting in a fire or shock hazard. You can use the chart below to calculate the required box size. Add up the numbers for the correspond- ing components in the box to find how many cubic inches you’ll need. In most cases, I skip the math and just buy the largest volume box available in the style I need. I’ve never been frustrated by having a box that was too large.

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