The National Electrical Code (NEC) is a set of standards created by the National Fire Protection Association (NFPA) for safe electrical installation. These standards are designed to prevent electrical hazards, ensure all installations meet local building requirements, and are updated to reflect new findings and technologies. The NEC has also published a consolidated version of the code specific to residential wiring in one and two-family dwellings . For those planning to redo or install outdoor electrical wires in systems with a voltage over 120V, it is important to follow NEC guidelines in order to ensure a safe and proper electrical installation. Most outdoor low-voltage (120V or less) systems, such as low-voltage landscape lights, that are added to your existing system are not regulated by the code. Check with a local electrician to make sure your low-voltage system is not regulated by local codes. Additionally, the version of the code that different buildings follow may vary based on location. You should always consult a certified electrician based on your location to make sure you follow the specific guidelines for your particular area.
As specified in NEC 406.9(A), the NEC code for outdoor receptacles requires that all outdoor receptacles installed in a damp location must have a weatherproof enclosure for when the cover is closed. These locations include roofed porches and patios that are not exposed to extensive rain or water. Outlet box covers must be able to open at least 90 degrees on a hinge, and outdoor 125 and 250-volt non-locking receptacles must be listed as weather-resistant.
According to NEC 406.9(B), 125 and 250-volt outdoor receptacles in wet locations must have a weatherproof enclosure even when a plug is or is not inserted. Outlet box covers for wet locations must be listed as extra-duty and should also open at least 90 degrees when on a hinge. 125 and 250-volt, and 15 and 20 amperes non-locking receptacles must be listed as weather-resistant. All enclosures rated for wet locations can also be used for receptacles in damp locations.
The National Electrical Code requires outdoor receptacles to be installed at both the front and back of a single-family house no more than 6.5 feet above the ground in accordance with 210.52(E). For multi-family houses, each grade-level unit must have at least one receptacle installed no more than 6.5 feet above ground. All decks and balconies must have a receptacle installed less than 6.5 feet above the deck surface. Additionally, all 125 and 250-volt outdoor receptacles must also have ground-fault circuit interrupters as specified in NEC 210.8(A).
The NEC has many regulations for underground electrical conduits and wiring. Underground feeders and other high voltage direct bury cables must be buried at least 2 feet deep in a trench unless you are using a conduit, which varies in burial depth depending on the conduit type. Use waterproof boxes to protect connectors and splices in direct bury cables. Low voltage (12-24 volt) wires are prohibited from being placed in the same conduit as 120/240-volt circuits, but they can be laid in the same trench as long as they are in separate conduits. All direct bury conductors must be listed for direct burial use. In order to prevent damaging any conduits or direct bury wires, backfill must not contain rocks, sharp angular substances, or corrosive materials as stated in 300.5(F).
The NEC code for underground conduits permits the following conduits for direct bury use in wet locations: Intermediate Metal Conduit, Rigid Metal Conduit, Liquidtight Flexible Metal Conduit (when listed and marked for the purpose), Rigid Polyvinyl Chloride Conduit, High Density Polyethylene Conduit, Nonmetallic Underground Conduit with Conductors, Reinforced Thermosetting Resin Conduit, Liquidtight Flexible Nonmetallic Conduit (when listed and marked for the purpose), and Electrical Metallic Tubing.
In accordance with NEC 300.5(A), all Type UF wires or other identified cables for landscape lights less than 30 volts must be buried at least 6 inches underground unless otherwise specified in the installation manual. Pool, spa, and fountain lighting wires under 30 volts and a part of a low-voltage system must also be buried at least 6 inches in the ground.
How deep should you bury an electrical conduit?: Outdoor conduit burial depth depends on the conduit type. PVC conduit must be buried at least 18 inches deep, while galvanized metal electrical conduits must be buried at least 6 inches deep.
How deep does an electrical PVC conduit need to be buried? : PVC conduit must be buried at least 18 inches deep.
Does outdoor wiring need to be in conduit?: Outdoor wiring needs to be in a conduit unless it is labeled as a direct bury or UF (underground feeder).
How deep does a direct burial wire need to be buried?: Low-voltage landscape direct burial wires must be buried at least 6 inches deep. All other direct burial wires need to be buried at least 24 inches below ground.
Does low-voltage wiring need to be in a conduit? : Whether or not you need a conduit for your low-voltage wiring depends on what types of wires and lights you are using. Direct burial low-voltage landscape wires in 12V and 24V that are connected to a transformer do not need to be in a conduit as long as you bury them 6 inches deep.
All outdoor low-voltage transformers and fixtures must be placed at least 5 feet from any pool or area of water, as stated in 680.22(A)(6). 680.23(A)(2) states that any transformer used to power underwater lights must be listed for pool or spa use. All transformers and power supplies must be Class 2 compliant.
Before digging, it is strongly recommended to call the national Call Before You Dig number at 811. Consult a certified electrician before making any changes to your outdoor electrical wiring.
Depending on the voltage, gauge, and distance away from your power source, your outdoor lights may experience an excessive voltage drop or dimming at the ends of your wiring system. The farther you place your lights away from the power source, the higher the internal resistance in the conductor which causes a decrease in voltage and therefore dimmer lights. In order to avoid excessive dimming, calculate the maximum run your system can handle and consider adding additional power sources, changing the wire gauge, switching to higher voltage landscape lights, or choosing low voltage transformers that offer multiple output voltages to compensate for voltage drop.
We recommend making a map or diagram of your outdoor wiring system to be used for future digging jobs and electrical changes. This will make sure you do not dig up existing wiring and will help you if you need to make changes to your outdoor wiring. Keep these documents with other house records.
