Outdoor Rough Wiring

Setting up Boxes

The weatherproof metal boxes used outdoors are made of a lightweight metal alloy rather than the thermoplastic or metal used in interior switch boxes. Outdoor boxes have wiring en try holes tapped for a common conduit size, usually % inch, in both ends and the back. Conduit threads to the box, as do cable connectors. Unused openings are closed with plugs furnished with each box. Boxes are sometimes supported by the rigid metal conduits threaded into them, or they’re mounted with screws on a firm surface.

Ordinary switches and receptacles are used outdoors. They are protected from weather by the integrity of the box in which they are mounted and by the design of the gasketed covers used with them. Outdoor- receptacle covers commonly have a pair of spring-loaded gasketed doors that close over receptacle openings when not in use. GFCI covers have a single door. The switch cover usually has a small shaft passing through it. A fork-shaped de vice that slips over the switch handle is connected to the shaft on the inside of the cover, and an operating lever is attached to the shaft on the outside. This design prevents water from entering the box through the cover opening.

Plastic outdoor conduit systems use PVC boxes and gasketed covers.

Generally, boxes should be mounted on rigid surfaces rather than depending only on conduit for support. This protects both the boxes and the conduit from damage. It’s also much easier to mount the boxes this way. The NEC allows conduit-only support of boxes that contain receptacles or switches only when two or more conduits are threaded into the box and the box is no more than 18 inches above the ground. Consider using pres sure-treated 4 by 4s to support your boxes. They can be set to any height.

Underground feeder (UF) cable should be the first choice for in-the-ground wiring. It’s approved for direct burial in the earth and in most cases requires mechanical protection only where it enters or leaves the ground. Both PVC and rigid metal conduit provide that protection. A bushing is required on the end of the conduit that's in the ground. If for some reason you choose, or are required to use, conduit in the ground, consider PVC first. It’s fast and easy to install, and installation doesn’t require special tools. PVC conduit and fittings also cost far less than rigid-metal-conduit systems.

Burial and Overhead Rules

A number of NEC rules govern the installation of underground wiring. Cables for 15-amp and 20-amp 120-volt branch circuits can be buried in a 12-inch-deep trench if the circuit has GFCI protection. Landscape lighting that operates at no more than 30 volts requires a trench just 6 inches deep when wired with Type UF or other identified cable. Rigid metal conduit also requires a 6-inch-deep trench.

Deeper trenches are required for larger branch circuits and feeders unless rigid metal conduit is used. A 60- amp feeder to a garage, for example, would require a 24- inch burial depth for direct- burial cables or conductors, and an 18-inch-deep trench if PVC conduit was being used. Where trenching is impossible—in solid rock, for example—rigid metal conduit or PVC conduit can be run across the rock surface if covered with 2 inches of concrete. Remember that wherever cables emerge from the ground, they must be protected from the bottom of the trench to a point 8 feet above grade, and that a bushing must be on the end of the protective conduit that's in the ground. Use rigid or Schedule 80 PVC for this protection.

Always leave some slack in the cable that's being put in the trench, and leave a small S in the cable at the point where the cable enters the protective conduit.

Taking electrical wiring outdoors allows the installation of lighting, receptacles for powered equipment, and pool and spa systems. Outdoor materials must be protected from weather foot traffic, and digging.

62 Outdoor Electrical Plan

Power source

63 Extending Cable or Conduit Underground:

Sheet plastic holds the dirt from the ditch; 3”-thick sod laid on sheet plastic

Sharpened iron pipe driven under the walk makes a hole for the conduit

Posts support conduit and boxes

The first section of conduit, from ti - - wired and assembled. The cable is section prior to assembly.

to the li by t h the pieces of the second

Outdoor Fixtures Middle-of-the-Run

Ready-mixed concrete

Ready-mixed concrete secures post

Trenches are usually back- filled with the material that was excavated. If that material is ordinary dirt or sand, there is no risk in simply laying cable in the trench and backfilling without providing extraordinary protection for the cable. However, protection is required where the presence of sharp rocks in the trench bottom and the backfill material may damage the cable. A bed and cover of sand, or running boards, will provide adequate protection. Also, if the trench passes through a garden or other area where future may occur, it's smart to co the cable with boards before backfilling. The inspector will want to see the trench before it's backfilled.

Outdoor light fixture; Outdoor Wiring Fixtures; Outdoor receptacle box and cover; Wood-post; End-of-the-Run; Bent conduit

For overhead services or feeders run overhead from the house to a detached building, such as a garage or workshop, service conductors must be run 10 feet above the yard and 15 feet above residential drive ways. Branch circuits and feed- era run overhead must be 10 feet above the ground and 12 feet above the driveway. Wires passing over roofs that can be walked on easily must pass at least 8 feet above the roof; other roofs require just 3 feet of clearance. Open conductors should not pass closer than 3 feet, measured horizontally, to windows and doors. If ever you add an open porch or deck to the house, these required clearances should be maintained.

Trenching Tricks

Trenching is usually done with a shovel, but when the trench is long or the ground is hard, think about renting a trencher. Route the trench well around large trees and other obstacles. More often than not, a trench must pass under a sidewalk or driveway at some point. Even when it's possible to dig under the pavement, it's usually unwise to do so. A good alternative is to drive a pipe through the ground at this point.

The pipe should not be too big; usually ¾-inch rigid conduit is large enough for No. 14 or. No. 12 two-conductor cable. It should be about one-and-a- half times the width of the pavement you are passing under. Drive the pipe with a 3- pound engineer’s hammer. The short handle and good balance of this tool make it easy to use when you are kneeling next to the trench. It’s also advisable to have a 14-inch pipe wrench on hand for rotating and extracting the pipe from the hole.

If you run into problems because of the width of the walk or difficulty with the soil, drive the pipe until it bogs down. Then, using a water hose and pistol-grip nozzle, make the tightest possible connection between the nozzle and pipe, and fully turn on the water briefly. Drive some more, then alternate between driving and water blasting until the pipe goes through. Don’t use any more water than necessary; too much could cause serious undermining.

Wiring Pools and Spas

Without adequate safeguards, water and electricity can be a lethal combination. That is why the NEC rules for wiring swimming pools, the equipment used with them, and the areas immediately adjacent to them are numerous and complex. To detail the rules here would be beyond the scope of this book. Here is a brief re view of the most important points, which may be enough to convince you that you probably should hire a licensed electrician to do the job. Your pool installer can recommend an electrician who is well versed in wiring swimming pools.

All metal parts within or attached to the pool and within the area 5 feet from the pool walls, measured horizontally for a distance of 12 feet above the pool, must be bonded to a common bonding grid. Metal piping, pump motors, metal- sheathed cable and raceways, and all electrical equipment associated with the pool water- circulation system must also connect to this grid.

In addition to this bonding, the electrical equipment in and near the pool, and any pool-associated motors, must be connected to an equipment grounding conductor. Pump motors that are clearly marked “double insulation” are exempt from this regulation.

65 Taking a Circuit Outside: Outdoor receptacle

Ground fault circuit interrupter (GFCI) protection must be provided for all branch circuits used in or near the pool.

Lights and switches can't be installed within 5 feet of the pool, and receptacles must be at least 10 feet away. However, one receptacle must be installed within 20 feet of the pool. There can be no underground wiring within 5 feet of the edge of the pool, and a pool can't be installed beneath an over head service. If you want to do the job yourself, professional pool installers should be able to help you with local regulations and practices. Make copies of Parts A and B of Article 680 from a library copy of the Code to study at home. Work with your local inspector; if the job isn’t going well, the worst thing that can happen is the inspector will recommend you hire a contractor to finish the job.

Minimum Cover* Requirements, 0 to 600 Volts, Nominal, Burial in Inches

Type of Wiring Method or Circuit

Direct Burial Cables or Conductors; Rigid Metal Conduit or Intermediate Metal Conduit; Rigid Nonmetallic Conduit Approved for Direct-Burial without Concrete Encasement or Other Approved Raceways;

Location of Wiring Method or Circuit

All locations not specified below

In trench below 2”-thick concrete or equivalent

Under a building

Under minimum of 4”-thick concrete exterior slab with no vehicular traffic and the slab extending not less than 6”beyond the underground installation

Under streets, highways, roads, alleys, driveways, and parking lots

One- and two-family dwelling driveways and parking areas, and used for no other purpose

In solid rock where covered by minimum of 2” concrete extending down to rock

* Cover is defined as the shortest distance measured between a point on the top surface of any direct-buried conductor, cable, conduit, or other raceway and the top surface of finished grade, concrete, or similar cover.

Note 1. For SI Units: one inch = 25.4 millimeters

Note 2 Raceways approved for burial only where concrete encased shall require concrete envelope not less than 2” thick

Note 3 Lesser depths shall be permitted where cables and conductors rise for terminations or splices or where access is otherwise required

Note 4 Where one of the conduit types listed in columns 1-3 is combined with one of the circuit types in columns 4 and 5 the shallower depth of burial shall be permitted.

Reprinted with permission from NFPA 70-1990 the National Electrical Code copyright. National Fire Protection Association Quincy MA 02269. This reprinted material isn't the complete and official position of the National Fire Protection Association on the referenced subject which is represented only by the standard in its entirety.

66 Low-Voltage Outdoor Lighting Systems

For inexpensive, easy-to-install lighting in a variety of forms for gardens, along walks, on decks, and so forth, low-voltage outdoor lighting kits are a sensible choice. The heart of the system is the power supply, which plugs into a 120-volt receptacle and supplies a safe low voltage, usually 12 volts, to power the lights. Some power supplies feature an electric eye that turns the lights on at dusk and off again at dawn. Installation is easy because the cable used in the system doesn’t have to be run in a trench, although it can be, and the fixtures are mounted on stakes that simply push into the ground.

Connections at the fixtures are made by pins that pierce the cable insulation when the cable is positioned between the fixture head and stake and the two parts are forced into their final location and pinned there. When assembling the system from components, be certain the intended power supply is large enough. Add up the lamp wattages, then choose a power supply that offers at least 25 percent more wattage.

Don’t use extension cords for permanent installations. It’s much better to install 120-volt receptacles in areas where the lighting system is planned to be established.