Install Outdoor Electric Wiring

Methods to get power from inside your home to another point outside (ie: pole mounted lantern), or other point that requires passing through the outside (ie: to a stand alone garage).

Steps

  1. Determine which method is the most desirable: direct burial of cable under soil, PVC electrical pipe (PVC) buried under soil with conductors installed in pipe, or aerial method. Each has its own benefits and detractors. Please read the entire article to help you decide which method will work best for you.
  2. Direct burial of type "UF" cable under soil is probably the most common and least expensive method. It provides for hot(s), neutral and ground conductors all inside a durable, sunlight and moisture resistant encasement or "jacket". UF type cable looks very similar to "NM" (Romex) cable, but differs in that the individual conductors are "flooded" with the jacket material found on NM cable. Thus, there is no thin, outer jacket to remove like NM cable, but rather the conductors and their insulation must be removed from the "jacket"(learning to do this may take a little time - practice with left over cable before attempting on installed cable). Direct burial cable requires at least an {{safesubst:#invoke:convert|convert}} deep trench in earth between the origin and termination of the lateral run. Most trenches should be dug to a depth that is below the frost line. Check with your inspector in your area to determine the minimum depth required.
  3. After ensuring the minimum depth along the entire length, lay type "UF" cable in the trench. Place smooth rocks on top of the cable to keep any high spots down.
  4. UF cable must be supported every {{safesubst:#invoke:convert|convert}}; just like NM cable. It does not need to be supported in the trench. This cable must be supported when run over concrete. This can be accomplished by securing wood (pressure treated if exposed to outdoors) to concrete and then securing the cable to the wood. If the cable may be subjected to physical damage, it should be "sleeved" in "Schedule 80" PVC pipe and terminated with proper pipe fittings (couplings, "LB" fittings, clips, expansion joints, etc).
  5. Do NOT backfill the trench until the electrical inspector or "authority having jurisdiction" (AHJ) has checked the work.
  6. PVC pipe method allows for adding circuits at will without the labor or expense of excavating again. By installing pipe a size or two larger than required for the current project, or providing a 2nd pipe at the same time, there will be enough room to pull in additional conductors later. Speed future installations by always leaving an extra "pull wire" or string for use to connect either a rope or directly to a new cable when the time comes to expand the number of circuits. Multiple pipes must provided for other services - low voltage and signal services such as: communication (telephone or network), cable TV, satellite television, intercom, etc. services are not permitted in pipes that contain power. These cables must either be installed in a separate pipe or buried directly within a cable labeled as suitable for direct burial in earth. It should be obvious that there is a great deal of flexibility offered by the (multiple) pipe method.
  7. A trench {{safesubst:#invoke:convert|convert}} deep minimum will be required for the pipe. Use "Schedule 40" for the portion under soil, and "Schedule 80" for those portions of the pipe run above ground. Layout the pipe run adjacent to the trench. Make sure you have a "snake" or fish tape long enough to go from end to end. Glue the pipe together with approved fittings and adhesives. Place the pipe into the trench.
  8. Secure the pipe where it rises above ground at {{safesubst:#invoke:convert|convert}} intervals with approved supports for the pipe.
  9. Do NOT backfill the trench until the wiring inspector has checked your work.
  10. A PVC "expansion joint" is often required between the point the pipe emerges from the ground and penetrates a wall or enters an enclosure mounted on the wall. Expansion joints allow for changes in grade that usually result from frost heaves, and must be employed where required. Check your local code for this requirement. Expansion joints are available at most home centers that sell PVC electrical pipe.
  11. Push the "fish tape" or "snake" in one end of the pipe until it exits the opposite end. Protect any existing wires from damage from the snake by placing cardboard or other insulator between the snake and wires at the opening of the pipe. Steel snakes will conduct electricity if allowed to rub through insulation of an energized wire, so shut off power if possible before installing the snake or pulling wire.
  12. Hook the conductors to the snake and tape together. Have a helper "feed" and guide the wires as you withdraw the snake from the pipe. Do not pull fast or hard, slow and steady tension is the key. Do not allow the new wires to constantly rub existing wires in the same place as they are pulled into the pipe, as doing so they may wear away insulation and expose harmful voltages present on the conductor(s) when energized.
  13. Aerial installations should only be done for short lateral runs, and where they may be installed so that traffic (vehicle or pedestrian) below will not create a hazard by contact. Additional clearance requirements must be observed when passing over roofs or near windows and doors.
  14. Type UF cable is suitable for an aerial run when used with approved strain relief fittings because Type UF cable is rated as / and accepted to be sunlight & moisture resistant. The strain relief and support fittings should be secured to the building framing members, not just to plywood sheathing of the structures. These fittings are seldom found in home centers, but are available at most full-line electrical distributors. This wiring method should be used only if the other two are not suitable. Keep in mind that these cables will stretch a bit when under high electric load or in direct sunlight. They will also be strained under the weight of snow and ice build up, and could break mid-span or rip from supports.

Tips

  • UF cable is most often NOT allowed to serve a pool pump and filter assembly. Check with your inspector. The PVC pipe method is however, suitable for pool pumps.
  • Circuits for use in garages and outdoors will most likely require Ground Fault protection.
  • UF cable generally is rated like its NM counterpart. 12-2 is a white and black insulated #12 wire and an uninsulated bare wire. 12-2 UF is suitable for connection to a 20 amp circuit.
  • PVC pipe is NOT a conductor. Remember to pull an insulated ground wire with EACH circuit. Most typical residential services are 240 volts, a ground is required for any single 120 volt circuit and each 240 volt circuit. Ground wire must be green (or taped / painted green at any place it is accessible) and be the same size and conductor material as the hot wire (but does not need to exceed #6 for copper).
  • Use electrical pipe and fittings only. Plumbing pipe and fittings of any kind (including black iron, copper, ABS and PVC) is NOT permitted for electrical installations.
  • Schedule 40 and Schedule 80 PVC have the same outside diameter, and use the same fittings. The difference between the two types (there are additional schedules, too), is their density. The Schedule 40 PVC has much less resistance to breakage from impacts, etc. than Schedule 80.

Warnings

  • Ask your inspector what depths are required for trenches in your area.
  • Show your inspector plans for aerial spans. Include drawings that show locations of windows, roofs and heights above grade.
  • Apply for a permit!
  • Swimming pools (and the like) have special considerations and as a result not covered in this wiki.

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