Choosing the Right Wire for Outdoor Lighting
The correct wire for outdoor lighting depends on whether you are installing line-voltage (120V) fixtures or low-voltage (12V) landscape lighting. Each type has different wire requirements, burial depths, and code considerations. Using the wrong wire outdoors creates safety hazards including shock risk, fire risk, and premature wire failure from moisture damage.
Line-Voltage Outdoor Lighting (120V)
Wire Type
For 120V outdoor lighting circuits, you need wire rated for wet locations and, if buried, rated for direct burial. The two standard options are UF-B (Underground Feeder) cable, which is a solid-jacketed cable rated for direct burial without conduit, and individual THWN-2 or THHN/THWN-2 conductors pulled through weatherproof conduit (PVC Schedule 40 or Schedule 80). UF-B is the most convenient option for simple outdoor lighting circuits because it can be buried directly in a trench without conduit. THWN in conduit is preferred for longer runs, larger installations, or locations where future wire replacement might be needed (pulling new wire through existing conduit is much easier than digging up direct-buried cable).
Wire Gauge
Most outdoor lighting circuits use 14 AWG on a 15-amp circuit or 12 AWG on a 20-amp circuit. The gauge depends on the total connected load and the circuit length. For a few exterior wall sconces or porch lights, 14/2 UF-B on a 15-amp breaker is adequate. For circuits powering multiple flood lights, post lights, and outdoor outlets, 12/2 UF-B on a 20-amp breaker provides more capacity and better voltage performance on longer runs.
Burial Depth
NEC requirements for burial depth depend on the wiring method. UF-B cable without conduit requires a minimum burial depth of 24 inches. UF-B cable under a concrete slab (like a driveway crossing) can be as shallow as the concrete thickness (typically 4 inches minimum). THWN conductors in PVC conduit require 18 inches of burial depth. THWN in rigid metal conduit requires only 6 inches of cover. GFCI-protected circuits in PVC conduit can be buried at 12 inches in residential installations.
Low-Voltage Landscape Lighting (12V)
Wire Type
Low-voltage landscape lighting systems operate at 12 volts through a step-down transformer and use special landscape lighting cable. This cable is typically a two-conductor stranded copper wire with a sunlight-resistant, direct-burial-rated jacket. It does not require conduit and can be buried just a few inches below the surface or laid on grade under mulch. Low-voltage landscape wire is available in gauges from 16 AWG to 8 AWG.
Wire Gauge Selection
Because low-voltage systems operate at 12V, they are very sensitive to voltage drop over distance. Using too thin a wire over a long run results in dim fixtures at the end of the line. For runs up to 50 feet with a total load under 100 watts, 16 AWG landscape wire is acceptable. For runs of 50 to 100 feet or loads of 100 to 200 watts, use 14 AWG. For runs of 100 to 150 feet or loads over 200 watts, use 12 AWG. For runs exceeding 150 feet or heavy loads, use 10 AWG or consider a hub wiring method (running a home-run cable from the transformer to a central point, then branching to fixtures in shorter runs).
GFCI Protection
All outdoor 120V outlets and lighting circuits must be GFCI protected per NEC 210.8. This can be accomplished with a GFCI breaker at the panel or a GFCI receptacle at the first outlet in the circuit. GFCI protection is not required for low-voltage landscape lighting circuits, though the transformer itself should be plugged into a GFCI-protected outdoor outlet.
IB Lighting carries UF-B cable, THWN conductors, and outdoor electrical supplies for both line-voltage and landscape lighting installations. Call (800) 674-9019 for pricing and project guidance, or browse our wire selection online.