Requirements for Exterior Underground Wiring

Code Variations

• Different states and towns have different electrical codes. Although there are many common elements to these codes, you should always check with your local authorities before beginning any wiring project.

Wire Type

• Underground wiring projects require underground feeder, or UF, wire. This type of wire has insulation on top of the copper and a layer of sheathing on top of the insulation for extra protection. It also has a fuse or circuit breaker at the end above ground, so that the power can easily be cut off as needed, or in the event of a power surge.

Depth

• In general, underground wiring should be buried a minimum of 24 inches below the surface. If it connects to a residential circuit that is rated for no more than 120 volts and 20 amps of current, the wiring can be buried just 12 inches below the surface. The deeper the wiring is buried, the less likely it is to be damaged accidentally by shovels or other digging equipment.

Protective Conduits

• Some locations require that all underground wiring be enclosed in protective conduits, which do help protect the wires from digging accidents. At a minimum, the wires should be encased in conduit wherever they bend and where they come out above ground. Wherever the wires might be moved, they must be placed in such a way that the movement cannot damage the wires or their connections.

Placement

• All wires that are connected to the same circuit should be carried in the same trench. Ideally, they should even all be part of the same cable. This will make any future repair work less complicated and less expensive.

Safety Equipment

• Underground wire must have a grounding conductor for safety. All equipment connected to underground wiring should be weatherproof, to reduce the chance of it shorting out.