How to Install an Exterior Junction Box With a Switch


The most troublesome part about installing an exterior electrical box is getting the cables to it, and if you're wiring a switch, you'll need at least two. Unless they are coming through the siding, you have to run them in conduit, and if the box is in the garden or on a fence, you may have to run them underground. None of that is difficult to do; it just means more work. Mounting the box itself is a simple task. Exterior boxes are waterproof and attach to siding, poles and fences with screws.

Things You'll Need

  • Screwdriver
  • Hammer
  • Pliers
  • Two conduit fittings and wire clamps
  • Adjustable pliers
  • Torpedo level
  • 1-inch wood screws
  • Drill
  • 1/2-inch drill bit
  • Conduit
  • Utility knife
  • Wire stripper
  • Wire cap
  • Knock out holes in the box for the electrical cables you need. If the cables are coming through the wall, knock out a hole in the back, using a screwdriver, hammer and pliers. If the cables are coming from outside, you'll need holes in the sides, top or bottom, depending on the wiring configuration.

  • Screw a conduit fitting and a wire clamp to each of the holes you knock out in the top, bottom or sides. Tighten the fittings with adjustable pliers.

  • Position the box, level it with a torpedo level and screw it to the siding, a post, a fence or some other solid substrate. Use 1-inch wood screws if no screws are supplied with the box. If the wires are coming through the siding, drill a 1/2-inch hole for them before setting the box, and position the box so that the hole in the back aligns with the hole in the wall.

  • Feed the two electrical cables you will attach to the switch to the box -- being sure that neither of them is live. Run them inside conduit or behind walls as needed. If you're using conduit, connect it to the fittings on the box with appropriate connectors.

  • Pull the cables out of the front of the box, giving yourself about 6 inches of slack with which to work, and strip off the plastic coatings with a utility knife. Separate the wires and strip the end of each insulated wire with a knife or a wire stripper.

  • Connect one of the black wires to one of the switch terminals and the other black wire to the other terminal. The wires and terminals are interchangeable. Tighten the terminal screws with a screwdriver.

  • Twist the two white wires together with pliers and screw on a wire cap. Twist the two ground wires together and attach one of them to the green ground screw on the switch.

  • Install the cover on the box. Most models have a rubber gasket that goes onto the box before you screw on the cover plate. The cover plate may have a hinged, spring-loaded weatherproof cover. If so, and cover swings vertically, install the plate so that the hinge is at the top.

Tips & Warnings

  • If you install the box on the siding, and the wire comes from inside the house, seal the box against rain by spreading silicone caulk between the back of the box and the siding.
  • If you're working with a circuit wire that is connected to the panel, turn off the breaker controlling it before doing any wiring, or you could be shocked.

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