When installing patio string lights, choosing the right gauge (thickness) of wire is an important decision. The wire size impacts safety, electricity costs, and the maximum length of your lighting run. In this comprehensive guide, we’ll walk through the key factors to consider when selecting patio lighting cable.
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Wire Gauge for Patio Lights
Wire gauge refers to the thickness of the copper conductor inside the cable. The gauge is represented by a number – the lower the number, the thicker the wire. Typical options for patio lighting wire are:
- 18 gauge
- 16 gauge
- 14 gauge
- 12 gauge
18 gauge is the thinnest option, while 12 gauge is the thickest. Heavier gauges (thicker wires) allow more electricity to flow through with less resistance and less voltage drop. But they also cost more and are less flexible. So what’s the best gauge for patio lights?
12 Gauge Wire
12 gauge patio lighting cable consists of a solid 12 AWG copper wire inside a protective PVC jacket. Key features:
- Allows up to 20 amps of electricity
- Low 3.5% voltage drop per 100 ft run
- Can make very long runs up to 200 ft from the transformer
- Thickest, most expensive, and least flexible option
Because of its extra capacity, 12 gauge wire is best for very long runs or when powering high wattage bulbs. It’s overkill for most small patio lighting projects.
14 Gauge Wire
14 gauge contains a solid 14 AWG copper conductor. Features include:
- Handles up to 15 amps
- Voltage drop of 5.5% per 100 ft run
- Suitable for runs up to 150 ft from transformer
- Good balance of capacity and flexibility
14 gauge patio wire works well for most medium-sized patios. It allows reasonably long runs with minimal voltage drop. It’s a nice middle-ground option.
16 Gauge Wire
16 gauge cable has a 16 AWG copper wire inside. Key attributes are:
- Good for up to 13 amp circuits
- Voltage drop of 8.5% per 100 ft
- Don’t run more than 100 ft from transformer
- Most flexible, easy to work with
16 gauge is a great choice for smaller patio lighting projects, like accenting a patio table or lighting a short run around a gazebo. It’s easy to install around corners but lacks capacity for long runs.
18 Gauge Wire
18 gauge contains very thin 18 AWG copper wiring. Characteristics are:
- Handles under 10 amps
- 13.5% voltage drop per 100 feet
- Only for runs under 50 feet
- Most flexible option
We don’t recommend 18 gauge wire for most outdoor installations, as its lacks capacity for all but the shortest runs. However, it can occasionally be useful for accent lighting small decor items.
Voltage Drop
Voltage drop refers to the loss of electrical power that occurs as electricity travels through the wire. Some amount of drop is inevitable. But if the drop is too large, your patio lights will be dimmer at the end of the run than at the beginning.
Voltage drop increases as the wire gauge gets thinner and the run gets longer from the transformer. You can use the voltage drop specs above to calculate whether drop will be an issue for your installation.
Max Run Length by Wire Gauge
The wire gauge sets a maximum recommended run length from the transformer, based on limiting voltage drop. Refer to this handy table for guidelines:
| Wire Gauge | Max Run Length |
|---|---|
| 12 gauge | 200 ft |
| 14 gauge | 150 ft |
| 16 gauge | 100 ft |
| 18 gauge | 50 ft |
Measure the linear distance from your transformer to the farthest outlet to see if it falls within the limits for your chosen wire thickness.
Outdoor Wire Considerations
When running patio lighting wire, you need cable designed for outdoor use. Look for the following features:
- Weatherproof jacket – The outer PVC insulation should repel moisture.
- UL listing – Wire should be safety tested for outdoor installation.
- UV resistant – The jacket should resist sun damage and cracking over time.
- Flexible – Wire needs to bend easily around corners and posts.
- Direct burial rating – If burying wire, ensure it’s rated for underground use.
These protections allow patio lighting cable to withstand sun, rain, snow and soil without breaking down prematurely.
Low Voltage vs. 120V Wire
Patio string lights normally use low voltage wire, which transforms 120V household power into 12V used by the lights. Benefits include:
- Safer to work with than 120V
- Lower voltage drop over distance
- Less expensive copper wiring
However, low voltage wire runs require a plug-in transformer. Occasionally 120V cable is used for short hardwired runs that don’t need a transformer. But low voltage is the typical choice.
Number of Conductors
Outdoor lighting wire contains multiple copper conductors inside the outer jacket:
- 2 conductor – 2 parallel wires to form a 12V circuit
- 3 conductor – Hot, neutral and ground wires for 120V
2 conductor cable is most commonly used with 12V patio lighting systems. 3 conductor can be used for some hardwired 120V installations.
Cost Comparison
The heavier the wire gauge, the more copper is used, which raises the cost. Expect to pay around:
- 12 gauge – $0.50+ per ft
- 14 gauge – $0.30 – $0.40 per ft
- 16 gauge – $0.20 – $0.30 per ft
- 18 gauge – $0.10 – $0.20 per ft
Carefully measure the total length you need and multiply by the per/foot cost to budget for your wire purchase.
Installation Tips
Here are some handy tips for safely installing patio lighting cable:
- Use cable staples to neatly attach the wire every 1-2 ft along its run.
- Avoid running wire close to the ground where it may puddle or get damaged.
- Seal all connections with silicone caulk to prevent moisture ingress.
- Connect the transformer to a GFCI outlet for safety near water.
- Keep wire runs as short as possible to limit voltage drop.
- Group multiple lights on one long run, instead of individual runs for each light.
Taking the time to properly install the patio lighting cable will pay off in lighting that lasts for many years outdoors.
Choosing a Transformer
The transformer converts high voltage electricity into 12V power for the patio lights. When selecting a transformer, you need to match its capacity to your lighting needs. Check the following:
- Wattage – Add up total bulb wattage and choose a transformer rated for at least 25% more capacity.
- Volts – Match the 12V or other low voltage output to your lights.
- Connector size – The wire connectors must be large enough for the cable gauge you’re using.
- Indoor/outdoor – Ensure the transformer is water resistant for outdoor use.
A properly sized transformer will provide safe, reliable power to your patio lighting.
Conclusion
Choosing the right gauge patio lighting wire involves balancing cost, run length, bulb wattage, and ease of installation. For most small- to medium-sized patios, a middle-ground option like 14 gauge is a good choice. Use the voltage drop estimates to size your wire run lengths. And be sure to use high quality, outdoor rated cable and a matching capacity transformer. With the right wiring in place, you’ll be able to enjoy the ambiance of your patio lights for many years.