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Do-It-Yourself Weekend Project #107
"How to Install Outdoor Wiring"

Tool and Material Checklist

Cable (wire) for exterior use (check codes), Outdoor switches, Outdoor receptacles, LB fittings, Box extenders, GFI, Tiling spade, Electric drill, Masonry bits, Lighting devices, Lineman pliers, Wire strippers, Wire nuts, Electrician's tape

Exterior wiring is different than interior wiring because water and extreme dampness are involved. Outdoor wiring projects are not difficult for a do-it-yourselfer, but, for safety reasons, outdoor wiring codes must be followed. Outdoor wiring projects fall into two general categories: functional and decorative. Functional lighting illuminates high-use areas such as steps, stairs, gates, walkways, and outdoor grills. Decorative lighting adds dimension and mood to exterior space such as highlighting tress and shrubs with light. Functional lighting can also be decorative.

Local Codes First, contact the municipal building inspector to determine the requirements for outdoor wiring, if the home center or building material outlet where you do business doesn't know.

Sometimes these retailers service many different communities with many code variations, and, therefore, may not know specific codes in your specific neighborhood. In some areas, only a professional electrician can make the final electrical hookup. In other areas, the work must be inspected before it can be put into operation.

Find out if local code permits the use of Type UF cable, or if it specifies Type TW wire and conduit. Generally, local codes require that outdoor wiring be protected by conduit in an instance in which outdoor wiring is installed above ground. If wiring will be buried, most codes allow Type UF cable. However, some require that Type TW wire and conduit be used.

The National Electrical Code now requires No. 12 gauge wire for all residential electrical wiring.

Ground Fault Interruptors

Ground fault interruptors (GFI) are now required by the National Electrical Code (NEC) in all outdoor areas.

A GFI is an electronic device that supplements conventional circuit breakers or fuses. The device electronically compares amperage flowing through the hot wire to amperage flowing through the neutral wire. If the circuit is not leaking current, amperages will be equal. But if there is a difference of as little as 1/200 of an ampere, the GFI detects the loss of current and automatically cuts off power within 1/40 of a second. This can save your life.

Types of Cable

Type UF is covered by heavy plastic sheathing. The cable is designed for placement in the ground without being encased in protective metal conduit.

Type TW wire has a thin thermoplastic insulation that provides the wire with some measure of moisture resistance. However, for maximum protection, the wire has to be encased in conduit.

Outdoor Switches

Heavy cast metal is used for switch boxes that will be mounted outdoors. Cover plates for the boxes are made from the same material and are outfitted with weatherproof gaskets.

Outdoor Light Fixtures

These boxes possess the same characteristics as boxes for outdoor receptacles. To inhibit moisture, there is a gasket made of the same material as the gasket in an outdoor receptacle installation. This seals the joint between the fixture box and the fixture box cover plate. (Also be sure to use weatherproof bulbs. They resist shattering when the temperature drops.)

Connectors and Fittings

LB fittings are right angle connectors that are used with conduit to bring cable through the wall of a house. The connectors are fitted with thick gaskets and metal cover plates so that they are impervious to moisture.

Box extenders are used when tapping an existing outdoor receptacle or fixture junction box for power. The extenders may be outfitted with a nipple and 90-degree elbow so that wires may be brought from the fixture, through conduit, to the point where power is wanted.


Three kinds of conduit are made for outdoor use. Rigid aluminum and rigid steel conduit provide equivalent protection to the wires that go through them. Rigid aluminum is easier to work with, but if it is going to be buried in concrete, first coat it with bituminous paint to prevent the conduit from corroding. Rigid plastic conduit is made from either polyvinyl chloride (PVC) which is normally used above ground, or high-density polyethylene, which is suitable for underground. If PVC is going to be exposed to direct sunlight, cover it with two coats of latex paint to prevent deterioration.

Although each type of conduit is available in a variety of diameters, conduit that is 3/4-inch in diameter will usually suffice around the house. This is wide enough to accept one AWG No. 12/3 UF cable or nine individual AWG No. 12 wires. AWG: American Wire Gauge, an industry standard.

Each type of conduit is available in a variety of fittings, including elbows, offsets, bushings, couplings, and connectors. If offsets and elbows don't provide the necessary turns in rigid metal or EMT conduit, you will need a hickey, a bending tool. A hickey sometimes can be rented. If not, the cost is not prohibitive, usually under $10.

Power from the Basement

Follow these guidelines for bringing electricity from a basement to the outside of a house. CAUTION: Turn off the power, if it is on the working circuit, at the main electrical box before starting any electrical work. Do not work with the power on.

1. Pick a reference point on an exterior wall that is identifiable on both the inside and outside of the house.

2. Inside the basement, measure from the reference point to a spot on a wall through which electricity can be brought. The spot should be at least 3 inches from a joist, sill plate or floor. The space is needed for the thickness of a junction box.

3. Outside the house, measure from the reference point to the power exit. Be sure the spot does not fall on a joint between bricks or blocks. The spot has to have a firm base for a LB fitting.

4. Outside, drill a 1/8-inch hole through the wall to verify that the path is clear. Blocks below the top row usually have hollow centers and are easier to drill.

5. Cut the opening for the extender, using a star drill and baby sledge hammer or an electric drill and masonry bit. Wear safety glasses and gloves when working with concrete.

6. Inside, open one end of the knockout holes from the back of a junction box, and then mount the box so the knockout hole coincides with the hole in the wall. Fasten the box to the wall with lead or fiber screw anchors and flat head screws driven into the anchors.

7. Outside, dig a trench for the cable.

8. Onto an LB fitting, screw a nipple long enough to extend from inside the junction box through the hole in the wall to the outside.

9 Outside, attach conduit to the LB fitting and run the conduit down the side of the house to the trench. Use conduit straps or hangers to hold the conduit.

10. Seal the joint around the LB fitting with a quality caulking compound such as silicone.

11. Inside, secure the nipple to the junction box with a connector. Install a plastic bushing over the connector to protect the wires or cable.

12. Pull the cable through the conduit and make the necessary connections to receptacles and switches.

Power from the Attic

These fittings are required to bring power from an attic to the outside: an outdoor outlet box, nipple, 90-degree corner elbow, conduit long enough to extend down the side of the house to the cable trench. Follow these guidelines:

1. Turn off the power on the circuit you will be connecting to the outdoor cable.

2. Position the assembly against the overhang (soffit) so the box and nipple are against the soffit and the conduit is against the siding. Try to run the conduit next to a downspout to hide it.

3. Mark the soffit where the cable from the power source in the attic will pass through the soffit into the outdoor outlet box. Drill a hole in the soffit for the cable. Drill pilot holes to accept No. 8 wood screws to hold the outlet to the soffit.

4. Run the cable from the power source in the attic out the hole in the soffit. Fasten the cable to the box with a 2-part cable connector and then screw the box to the soffit.

5 With conduit straps, strap the nipple and conduit into place and run the conduit down the siding to the trench that you will dig.

6. Once the cable has been laid to the new junction box, hook up the wiring to the existing power feed wire of an existing switch or outlet.

The Trench

When laying out a path for the trench from the house, try to make the path straight. If you can't, make the bends gradual curves, not sharp turns.

1. Outline both sides of the trench with stakes and string. The trench should be 4 inches wide.

2. Cut along the string outline to a depth of 3 to 4 inches. Use flat tiling space. Dig out the sod and lay it on plastic sheeting. keep it damp until the sod is relaid. Don't soak it; just sprinkle it with water.

3. Dig the trench. If you are using EMT conduit or UF cable, the trench should be 12 inches deep. Rigid metal or plastic conduit requires a 6-inch depth. Check the local utilities for a buried pipe/wire site plan before you start digging. If you have lots of trenching to do, rent a power trenching tool or call in a pro for the job.

Free-Standing Receptacles

An outdoor receptacle should be at least 12 inches above the ground level and must be securely anchored underground. Do this by laying the cable or conduit either through the center opening of a concrete block or through a coffee can in which you place concrete to stabilize it as a unit.


By National Electrical Code, all splices must be made inside an outlet, junction or switch box. The splices must be made with Wire Nuts. It also is suggested that the nuts are wrapped lightly with electrician's tape for added safety and neatness. Connections to terminals are made with wire ends looped in the direction the terminal turns, clockwise. This way, the wire is tightened under the terminal screw.

Strip about 3/4-inch of insulation from the wire. Use wire strippers for this, putting the wire in slot #12 of the stripper handle and rotating it 360 degrees. If cable, strip the outer insulation from it about 6 inches so the wires may be positioned easily. Lay the cable on a flat solid surface and use a pocketknife or a utility knife (or cable stripper) to remove the outer insulation. Be careful not to cut the insulation on the wires inside of the cable insulation. Easy does it.

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