Burial depths, conduit requirements, GFCI protection, wet-rated fixtures, and low-voltage systems
Outdoor electrical installations include both line-voltage (120V) systems for outlets, outdoor lights, and appliances, and low-voltage (12V/24V) systems primarily for landscape lighting. Each has distinct requirements for safety and code compliance.
Outdoor wiring must withstand moisture, temperature extremes, UV exposure, and physical damage. Proper burial depths, conduit protection, GFCI protection, and weatherproof enclosures are essential for safe, long-lasting installations.
| Wiring Method | Residential (Under 120V) | Under Driveway/High Traffic | Notes |
|---|---|---|---|
| Rigid Metal Conduit (RMC) | 6 inches | 6 inches | Most durable, best for shallow burial |
| PVC Conduit (Schedule 40) | 18 inches | 18 inches | Most common, economical, easy to work with |
| Direct Burial Cable (UF-B) | 24 inches | Not allowed | No conduit, but requires deeper burial |
| UF Cable in PVC (2" or more cover) | 18 inches | 18 inches | Combines protection with code-minimum depth |
| GFCI Protected Circuit | 12 inches | 18 inches | Reduced depth when GFCI protected, PVC conduit |
Low-voltage (12V or 24V) landscape lighting wire has different requirements:
| Conduit Type | Material | Common Sizes | Best Use |
|---|---|---|---|
| PVC Schedule 40 | Rigid PVC plastic | 1/2", 3/4", 1" | Underground burial, most outdoor applications |
| PVC Schedule 80 | Thicker PVC (gray) | 1/2", 3/4", 1" | Above-ground outdoor, exposed locations |
| Rigid Metal Conduit (RMC) | Galvanized steel | 1/2", 3/4", 1" | Above-ground, physical protection needed |
| IMC (Intermediate Metal) | Lighter-wall steel | 1/2", 3/4", 1" | Above-ground where RMC is too heavy |
| EMT (Electrical Metallic Tubing) | Thin-wall steel | 1/2", 3/4" | NOT for direct burial, dry locations only |
| Liquid-Tight Flexible | Flexible plastic-coated | 1/2", 3/4" | Short runs to outdoor fixtures, AC units |
When bringing underground conduit above grade:
Ground Fault Circuit Interrupter (GFCI) protection is required for virtually all outdoor receptacles and many outdoor lighting circuits to prevent fatal electric shocks in wet conditions.
| Application | GFCI Required? | Notes |
|---|---|---|
| Outdoor Receptacles (All) | YES | All outdoor outlets, regardless of use or height |
| Outdoor Lighting (attached to house) | No | Wall-mounted lights controlled by indoor switch |
| Outdoor Lighting (detached, 120V) | YES | Post lights, landscape 120V lights require GFCI |
| Low-voltage lighting (12V/24V) | No | Transformer primary should be GFCI protected |
| Pool/Hot Tub Equipment | YES | Special requirements, separate article in NEC |
| Outdoor Kitchen Appliances | YES | Refrigerators, grills, all receptacles |
Install GFCI receptacle as first outlet in circuit. Protects all downstream outlets when wired correctly (load terminals). Most common for outdoor circuits.
Replaces standard breaker at panel. Protects entire circuit. More expensive but convenient. Good for multiple outdoor circuits.
Plug-in GFCI for temporary protection. Not code-compliant for permanent installations. Use for power tools when working outdoors.
Outdoor fixtures must be rated for their exposure level. Using indoor or damp-rated fixtures in wet locations creates shock hazards and premature failure.
| Rating | Water Exposure | Typical Locations | Features |
|---|---|---|---|
| Dry Location | No moisture exposure | Indoor areas, protected from weather | Standard fixtures, no weatherproofing |
| Damp Location | Protected from direct water, moisture present | Covered porches, eaves, enclosed soffits | Moisture-resistant gaskets, limited sealing |
| Wet Location | Direct exposure to rain, snow, sprinklers | Exposed yard lights, open patios, landscape | Fully sealed, weatherproof gaskets, rated IP65+ |
Low-voltage landscape lighting uses a transformer to step down 120V AC to safe 12V or 24V. This safer voltage allows DIY installation without permits in most areas and eliminates shock hazards.
| Transformer Size | Total Wattage Capacity | Typical Number of Lights | Best Use |
|---|---|---|---|
| 150W | Up to 120W (80% rule) | 8-12 LED fixtures (10W each) | Small yards, pathway lighting |
| 300W | Up to 240W | 16-24 LED fixtures | Medium yards, standard residential |
| 600W | Up to 480W | 32-48 LED fixtures | Large yards, extensive lighting |
| 900W+ | Up to 720W+ | 48+ LED fixtures | Commercial, very large properties |
Sizing Rule: Add up wattage of all lights, then multiply by 1.25 (80% rule). Choose transformer with capacity equal to or greater than this total.
| Wire Gauge | Maximum Run Length | Total Wattage Capacity | Notes |
|---|---|---|---|
| 18 AWG | 15 feet | Up to 25W | Very short runs only, not recommended |
| 16 AWG | 30 feet | Up to 50W | Short runs, minimal voltage drop |
| 14 AWG | 50 feet | Up to 100W | Most common, good balance |
| 12 AWG | 100 feet | Up to 200W | Long runs, large yards |
| 10 AWG | 150+ feet | Up to 300W | Very long runs, commercial |
For most residential landscape lighting:
Map out light locations. Count fixtures and total wattage. Add 25% for transformer sizing. Determine wire gauge needed based on run lengths.
Mount transformer near outdoor GFCI outlet, 12-18 inches above grade. Plug into GFCI outlet. Ensure easy access for timer adjustments.
Lay wire along planned route before burying. Use landscape flags to mark light locations. Test route for proper coverage before trenching.
Dig 6-inch deep trenches along wire routes using flat spade or trenching tool. Keep trenches narrow to minimize landscape disruption.
Use waterproof connectors (quick-connects or wire nuts with silicone). Strip wire carefully without nicking strands. Test connections before burying.
Install stakes or mount fixtures at marked locations. Aim spotlights at features. Position path lights 6-10 feet apart for even coverage.
Connect wire runs to transformer terminals. Most transformers have multiple taps (12V, 13V, 14V, 15V) - start with 12V tap. Tighten terminal screws securely.
Turn on transformer and verify all lights illuminate. Check voltage at furthest fixture (should be 10.8V minimum). Adjust transformer tap if needed.
Place wires in trenches and backfill with soil. Leave small service loop at each fixture for future adjustments. Tamp soil gently to avoid damaging wires.
Set timer for desired on/off times or configure photocell. Adjust light positions and aim after dark. Test system for several nights before finalizing.
Note: Line-voltage outdoor electrical work requires permits in most jurisdictions and must comply with NEC and local codes. Low-voltage landscape lighting generally doesn't require permits but should follow manufacturer guidelines. Consider hiring a licensed electrician for 120V outdoor installations.
Disclaimer: This guide provides general information about outdoor and landscape electrical installations. Local codes, soil conditions, and climate may require different approaches. Line-voltage outdoor electrical work can be dangerous and typically requires permits and inspections. Always call 811 before digging, follow NEC and local codes, and consider hiring a licensed electrician for 120V outdoor installations.