Choosing the right kind of wire for outdoor lighting is an important decision that requires careful consideration of several factors. The type of wire you use needs to be rated for exterior use and able to withstand exposure to the elements. It also needs to be the proper gauge to handle the voltage and wattage requirements of your lighting fixtures. In this article, we will discuss the key factors to consider when selecting wire for outdoor lighting and provide recommendations on the best types of wire to use for different scenarios.
Page Contents
Key Factors When Choosing Outdoor Lighting Wire
There are several important factors to take into account when selecting the right wire for your outdoor lighting:
Outdoor Rating
Any wire used for exterior lighting must be specifically rated for outdoor use. Look for wire that is UL (Underwriters Laboratories) listed for outdoor wet locations. The insulation and jacket materials will be resistant to UV rays, moisture, and temperature extremes.
Wire Gauge
The gauge, or thickness, of the wire must be suited to the voltage and wattage of the lighting fixtures. Thicker wires (lower gauge numbers) are used for higher wattage loads over longer distances. Thinner wires (higher gauge numbers) can be used for lower wattage loads over shorter distances.
In-Ground vs. Exposed Wiring
Wiring that will be buried underground requires insulation rated for direct burial. Exposed wiring used above ground should have weather-resistant insulation. Consider also if the wiring will be subject to physical damage and select wire with tough reinforced insulation.
Single Stranded vs. Solid Core
Stranded wire is more flexible and is the better choice for applications where the wiring will experience movement or vibration. Solid core wire is stiffer and more prone to breaking when flexed, but is easier to work when making connections.
Length of Run
The total length of the wire run from the power source to the lights and between each light must be taken into account based on the wire gauge and fixture wattage. Longer runs may require thicker gauge wire than short runs for the same lights.
Types of Outdoor Lighting Wire
Now that we’ve reviewed the key factors, here are some of the most common types of wire used for outdoor lighting and the best applications for each:
THWN Wire
THWN wire has a thermoplastic insulation rated for wet locations, a nylon jacket, and can resist temperatures up to 194°F. It is very durable and moisture resistant, making it a great general-purpose outdoor lighting wire for both exposed and underground uses. THWN works well for landscape lighting, pathway lighting, and string lights.
UF Cable
UF (underground feeder) cable is designed specifically for direct burial in the ground. It consists of insulated wire cores wrapped in a moisture-resistant thermoplastic jacket, making it ideal for in-ground wires running to post lights, deck lights, or other permanent fixtures. It comes in 2-4 wire configurations.
TW Wire
TW (thermoplastic heat and water resistant) wire is rated for wet locations, resists high temperatures up to 176°F, and has a moisture-resistant thermoplastic insulation jacket. It is more rugged than standard THHN wire and is a good choice for outdoor fixtures subject to physical abuse.
High-Temperature Wire
Fixtures like spotlights or floodlights may require wire rated for even higher temperatures. Look for TEW or MTW wire rated for temperatures up to 221-257°F for those applications.
SPT-3 Cable
For temporary or removable lamps like holiday lights, SPT-3 cable works well. It contains two insulated 16 or 18 AWG conductors and an uninsulated bare copper ground wire. Just make sure not to run it underground.
SOW Cable
SOW (service-entrance outdoor weather resistant) cable has an insulated ground wire and heavy-duty moisture resistant jacket – ideal for wiring outdoor receptacles, lights, or hardwired fixtures. Make sure to use the 3-wire version for power requiring a neutral.
Matching Wire Size to Lighting Fixture Wattage and Voltage
When running wire for outdoor lighting, follow basic electrical code requirements and guidelines on matching wire gauge to the voltage and wattage ratings of the connected lighting fixtures. Here are some examples:
12V Low Voltage Lighting
For 12V lighting systems, use 16 or 18 gauge wire for runs up to 50 feet from the transformer to light fixtures. Go up to 14 gauge for 50-100 ft runs, and 12 gauge for 100-150 feet. Keep voltage drop under 3% for optimal efficiency.
120V Lighting Circuits
For standard 120V household voltage, lighting circuits are often wired with 14 or 12 gauge. Here are some guidelines on selecting the proper gauge:
– 14 gauge up to 15A (1800W)
– 12 gauge up to 20A (2400W)
– 10 gauge up to 30A (3600W)
Increase wire gauge for longer wire runs over 100 feet. Use volt drop calculators to determine proper wire size.
240V High Power Lighting
For very high wattage fixtures running on 240V circuits, thicker wire gauges are required:
– 10 gauge up to 20A (4800W)
– 8 gauge up to 25A (6000W)
– 6 gauge up to 30A (7200W)
When in doubt, go up a size rather than down – oversized wire is safer than undersized.
Wiring Techniques and Installation Tips
Follow these techniques and tips for safe and effective installation of your outdoor lighting wires:
Make Waterproof Connections
Use connectors and junction boxes listed for wet locations. Avoid wire nut connections for outdoor wires. Seal all connections and ends with waterproof tape, silicone caulk, or heat shrink tubing.
Run Wiring Neatly
Use staples or clips rated for outdoor use to fasten the wire neatly along walls, posts, or beams. Do not allow wires to make contact with sharp edges or screws.
Install GFCI Protection
Outdoor lighting and receptacle circuits must have GFCI (ground fault circuit interrupter) protection. Install a GFCI breaker or outlet to protect against shocks.
Check Burial Depth
For underground wires, maintain a burial depth of 6-12 inches depending on wire type. Avoid shallow depths under 2 inches.
Separate Wires
Keep low voltage landscape lighting wires separate from 120V household wiring. If they intersect, cross them at 90 degree angles.
Test Before Energizing
Check for continuity, proper connections, and correct polarity before turning on electrical power to the wire.
Conclusion
Choosing suitable outdoor lighting wire involves matching the insulation type, temperature rating, and gauge to the specific lighting application. THWN, UF, TW, and high-temp wire are common choices for permanent fixtures. SPT-3 works for removable lamps. Follow electrical code for proper voltage drop, amp ratings, and wire sizing. Making robust moisture-proof connections, neat routing, and safe underground installation will give you reliable outdoor lighting wired to last.
| Wire Type | Description | Best Use |
|---|---|---|
| THWN | Thermoplastic heat and water resistant. Withstands wet locations and 194°F. | General purpose for landscape lighting, pathway lights. |
| UF Cable | Underground feeder cable. Direct burial rated moisture resistant insulation. | In-ground wiring to post lights or deck lights. |
| TW Wire | Thermoplastic heat and water resistant. Withstands 176°F wet conditions. | Outdoor fixtures subject to abuse. |
| High-Temp Wire | Withstands 221-257°F. TEW, MTW insulation. | High wattage spotlights and floodlights. |
| SPT-3 Cable | 2 insulated 16-18 AWG conductors and bare copper ground. | Temporary/removable lamps like holiday lights. |
| SOW Cable | Insulated ground, heavy moisture resistant jacket. | Outdoor receptacles, lights, hardwired fixtures. |
Wire Gauge Selection Guidelines
| Voltage | Wire Gauge | Breaker Rating | Max Wattage |
|---|---|---|---|
| 12V | 16-18AWG | 50W (50 ft run) | |
| 14AWG | 100W (100 ft run) | ||
| 12AWG | 150W (150 ft run) | ||
| 120V | 14AWG | 15A | 1800W |
| 12AWG | 20A | 2400W | |
| 10AWG | 30A | 3600W | |
| 240V | 10AWG | 20A | 4800W |
| 8AWG | 25A | 6000W | |
| 6AWG | 30A | 7200W |