How to wire a plastic junction box

Written by chris deziel Google
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How to wire a plastic junction box
Plastic junction boxes do not need to be grounded. (electrical box image by jimcox40 from

Whenever wires have to be joined together in home circuitry, you need a junction box. In very old homes, you might find capped-off wires behind the walls, but these are a fire hazard and are no longer allowed by the National Electrical Code. In some cases a receptacle or switch box may serve as a junction point, but if neither is available where the wires need to be joined, you have to install a junction box.

Skill level:
Moderately Easy

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Things you need

  • Plastic junction box
  • J-box cover
  • Hammer
  • Screwdriver
  • Utility knife
  • Pliers
  • Wire splicer
  • Twist-on wire connectors

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  1. 1

    Make sure the power is off before you begin.

  2. 2

    Nail the junction box into an available stud or rafter. J-boxes come with preset nails so you can easily to this.

  3. 3

    Feed the wires through the self-clamping openings in the back of the box. Feed through enough wire so you have about 8 inches to work with.

  4. 4

    Remove about 6 inches of sheathing from both wires by cutting around the circumference with a utility knife, being careful not to cut into the insulation on the wires inside.

  5. 5

    Strip about 1/2-inch of insulation from all black and white wires with the splicing tool.

  6. 6

    Hold the white wires together so the ends are parallel and twist them together clockwise with pliers. When they are securely joined, screw on a wire cap. Repeat with the black wires.

  7. 7

    Twist the ground wires together. You do not need to cap these.

  8. 8

    Screw the cover on with the screws provided.

Tips and warnings

  • Twist-on wire connectors come in many different sizes. Be sure you are using the correct size for the gauge of wire you are joining.
  • Although you can connect more than two wires in a j-box, there is a limit to how many wires the box is supposed to hold. Check your local codes.
  • Never cut into wires or splice them until you are sure the power is off. If you are not sure, use a voltage tester.

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