The National Electrical Code (NEC) includes many specific requirements for outdoor circuits and equipment. The primary safety concerns outdoors are moisture and corrosion, physical damage, and issues related to underground burial. With most residential outdoor wiring projects, the relevant code requirements pertain to installing outdoor receptacles and fixtures and running wiring above and below ground.
Where requirements call for "listed" equipment, products must be listed for the application by an approved testing agency, such as UL (formerly Underwriters Laboratories).
- GFCI (ground-fault circuit-interrupter) protection is required for all outdoor receptacles. Specific exceptions may be made for snow-melting or deicing equipment. GFCI protection can include GFCI receptacles or GFCI circuit breakers.
- Homes must have at least one outdoor receptacle at the front and rear of the house. They must be readily accessible from the ground and no more than 6 1/2 feet above grade.
- Attached decks and balconies with interior access (door to indoors) must have a receptacle no more than 6 1/2 feet above the deck or balcony walking surface. As a general recommendation, houses also should have a receptacle at each side of a deck or balcony, accessible from the ground.
- Receptacles in damp locations (under protective covers, such as a porch roof) must be weather-resistant and have a weatherproof (sometimes called weathertight) cover.
- Receptacles in wet locations (exposed to weather) must be weather-resistant and have a weatherproof "in-use" cover. This cover provides weather protection even when cords are plugged into the receptacle.
- Light fixtures in wet/exposed areas must be listed for wet locations.
- Light fixtures in damp areas (protected by an overhanging eave or roof) must be listed for damp locations.
- Surface-mounted electrical boxes for fixtures must be raintight/weatherproof.
- Exterior light fixtures do not require GFCI protection.
- Low-voltage lighting systems must be listed as an entire system or assembled from listed components.
- Transformers for low-voltage lighting must be accessible.
- Exposed or buried wiring/cable must be listed for its application. Type UF cable is the most commonly used nonmetallic cable for residential outdoor wiring runs.
- UF cable can be direct-buried (without conduit) with a minimum of 24" of cover.
- Wiring buried inside rigid metal (RMC) or intermediate metal (IMC) conduit must have at least 6" of cover; wiring in PVC conduit must have at least 18" of cover.
- Backfill surrounding conduit or cables must be smooth granular material without rocks.
- Low-voltage (no more than 30 volts) wiring must be buried at least 6" deep.
- Buried wiring runs that transition above ground must be protected in conduit from the required cover depth or 18" (whichever is less) to its termination point above ground or at least 8 feet above grade.
Call Before You Dig
This is not an NEC requirement, but it could save your life and/or considerable trouble with your service providers.
Call 8-1-1, the national "Call Before You Dig" hotline, at least three days before you plan to dig anywhere on your property. The hotline personnel will notify all utility providers in your area. Those with lines running through your property will send out a representative to mark their line(s) on the ground. You can use power equipment to dig no closer than 24" to marked lines; use a hand shovel when digging within 24" of either side of a marked line.