The SPT-1 vs SPT-2 wire decision comes up constantly in the Christmas light installation world, and there is more bad information about these wire types online than almost any other topic. After running ChristmasLightsHQ and working alongside thousands of professional installers in our 43,000-plus member community, I want to set the record straight on what SPT-1 and SPT-2 actually are, how they perform, and which one you should be using.
SPT stands for Service Parallel Thermoplastic. The number after it — 1 or 2 — refers to the insulation thickness. That is the only difference. As someone with safety certifications including Hazmat Tech and EMT, I take electrical safety seriously, and understanding your wire is part of doing the job safely and professionally.
How to Run Power for Christmas Lights
Watch these videos from our YouTube channel to see how we run electrical and route extension cords on real job sites. Understanding your wire choice matters most when you are planning and running your power.
What Is the Difference Between SPT-1 and SPT-2?
Here is the key fact that most online guides get wrong: both SPT-1 and SPT-2 use 18-gauge (18 AWG) copper wire, and both carry the same amperage. The wire inside is identical. The only difference is the thickness of the outer jacket — the plastic insulation covering the copper conductor.
SPT-1 has a thinner jacket (0.030 inches). SPT-2 has a thicker jacket (0.045 inches). That is it. Same wire gauge, same copper conductor, same electrical performance. Both can carry up to 10 amps on runs under 50 feet, and 7 amps on longer runs. The thicker jacket on SPT-2 simply provides more physical protection for the wire — better abrasion resistance, better UV protection, and better durability in harsh conditions.
| Specification | SPT-1 | SPT-2 |
|---|---|---|
| Wire gauge | 18 AWG | 18 AWG |
| Jacket thickness | 0.030 inches | 0.045 inches |
| Amperage (under 50 ft) | 10 amps | 10 amps |
| Amperage (over 50 ft) | 7 amps | 7 amps |
| Temperature rating | 105°C | 105°C |
| Flexibility | More flexible | Slightly stiffer |
| Cost per foot | Lower | 15-25% more |
The bottom line: there is no electrical advantage to SPT-2 over SPT-1. The advantage is purely physical durability of the jacket.
Why We Use SPT-1 for Most Installations
For seasonal temporary Christmas light installations with LED bulbs, SPT-1 is our standard wire. It is more flexible, easier to work with, costs less, and carries the same current as SPT-2. Since we are using LED C9 bulbs that only draw about 7 watts each (not amps — watts), the total current draw on even a very long run is minimal.
To put it in perspective, I recently completed a house with over 1,000 feet of C9 LED lights on 12-inch spacing, and we were pulling only about 5 amps total. That is well within the 7-amp rating for both SPT-1 and SPT-2 on long runs. With LED bulbs drawing so little power, the wire gauge and jacket type are almost never the limiting factor.
SPT-1 is the right choice for roofline installations, window and door framing, tree wraps, bush lighting, and any seasonal work where you are taking the lights down at the end of the season. It is more flexible, which makes it easier to wrap around trees and run along trim details. And since you are installing and removing it each year, the slightly thinner jacket is not a durability concern.
When to Use SPT-2 Instead
There are a few specific situations where SPT-2 makes sense over SPT-1:
Permanent installations: If you are leaving lights up year-round, SPT-2 is the better choice. The thicker jacket holds up better to continuous UV exposure, temperature cycling, and weather over multiple years without removal. Permanent lighting installations need that extra jacket protection.
Extremely cold climates: If you are installing in Canada or northern states where temperatures regularly drop well below zero, SPT-2's thicker jacket provides better cold-weather performance. The thicker insulation resists cracking and brittleness in extreme cold better than SPT-1.
Outside of those situations, SPT-1 is the standard for professional seasonal work. Don't let anyone tell you that you need SPT-2 for every outdoor installation — with LED bulbs and seasonal use, SPT-1 does the job perfectly.
How Far Can You Run LED Lights on SPT-1 Wire?
Much further than most online guides tell you. Those bulbs drew massive current. LED C9 bulbs draw about 7 watts each. At 120 volts, that is a tiny fraction of an amp per bulb.
We regularly run 500 to 1,000 feet of LED lights on 18-gauge SPT-1 wire without any voltage drop issues. As I mentioned, 1,000 feet of C9 LEDs at 12-inch spacing was pulling only 5 amps. That is well under the 7-amp limit for long runs on either wire type.
Your limiting factor with LED bulbs is almost always the circuit breaker capacity (typically 15 or 20 amps on a residential circuit), not the wire. Calculate your total wattage, convert to amps, and make sure you stay within the circuit rating. Voltage drop takes care of itself at these low current levels.
If you do see dimming on an extremely long run, split it into two shorter runs fed from separate power sources. We do not do power injection for seasonal christmas light installations — just split the run. For more on this, see our voltage drop guide.
How Do You Identify SPT-1 vs SPT-2?
The wire type is printed on the insulation. Look for "SPT-1" or "SPT-2" stamped along the length of the wire. If it is not printed, you can tell by feel and thickness.
SPT-1 has a total thickness of approximately 0.160 by 0.310 inches. SPT-2 has a total thickness of approximately 0.190 by 0.370 inches. SPT-2 feels noticeably thicker and stiffer in your hands. After handling both types a few times, you can identify them by touch alone.
When taking over a customer from another installer, check the wire type on the existing installation. Know what you are working with before you plug anything in.
What Wire Should You Stock?
Keep your inventory simple. For most seasonal installation businesses, SPT-1 is your primary wire.
| Wire Type | Stock Level | Primary Use |
|---|---|---|
| 18 AWG SPT-1 green | High | Roofline, trees, bushes, windows |
| 18 AWG SPT-1 white | Medium | White trim, eaves, fences |
| 18 AWG SPT-1 brown | Low | Tree trunks, wood surfaces |
| 18 AWG SPT-2 green | Low | Permanent installs, extreme cold climates |
Green wire accounts for over 70 percent of professional use. Stock it in bulk. White wire runs about 20 percent of jobs. Brown is specialty for specific wood-toned applications. For professional light kits, you will find the right wire type already matched to the job.
Common Wire Mistakes Contractors Make
Thinking SPT-2 is a different gauge wire. This is the most common misconception. Both SPT-1 and SPT-2 are 18-gauge wire. The difference is only the jacket thickness. Do not let anyone tell you SPT-2 is 18 gauge with a thicker jacket — it is not.
Believing you need SPT-2 for every outdoor job. For seasonal LED installations, SPT-1 is perfectly adequate and easier to work with. Save SPT-2 for permanent installs and extreme cold climates.
Thinking you can only run 150 or 200 feet. Those numbers were for older bulb technology. With LED C9s drawing only a few watts each, you can run many times that distance without issues.
Not checking wire type on pre-made strands. Budget pre-made light strands might use thinner wire than you expect. Know what you are buying and make sure it meets your standards.
Reusing damaged wire. Nicks in the insulation create short circuit risks. If the jacket is damaged, replace the wire. Safety is not negotiable.
Related Guides
- Voltage Drop in Christmas Lights: What Every Installer Must Know
- C9 Stringer Wire: How to Build Custom Runs
- GFCI Requirements for Christmas Light Installations
- C9 LED Christmas Lights: The Complete Guide
- How to Hang Christmas Lights on a Roof Like a Pro
Frequently Asked Questions
Are SPT-1 and SPT-2 the same gauge wire?
Yes. Both SPT-1 and SPT-2 use 18-gauge (18 AWG) copper conductors. The only difference is the jacket thickness — SPT-2 has a thicker outer insulation (0.045 inches vs 0.030 inches). Some guides incorrectly claim SPT-2 is 18 gauge with a thicker jacket wire, but that is not accurate. Both carry the same current: up to 10 amps under 50 feet and 7 amps on longer runs.
Do I need SPT-2 for outdoor Christmas light installations?
Not for seasonal work with LED bulbs. SPT-1 is the standard for temporary Christmas light installations. SPT-2 makes sense for permanent installations that stay up year-round, or for installations in extremely cold climates like Canada where the thicker jacket provides better cold-weather durability.
How far can I run LED C9 lights on SPT-1 wire?
Much further than most guides suggest. We have run over 1,000 feet of C9 LEDs on 12-inch spacing at only 5 amps total on SPT-1 wire. With LEDs drawing only about 7 watts per bulb, your circuit breaker capacity is the limiting factor, not the wire length. If you see dimming on a very long run, split it into two shorter runs.
Does wire color affect performance?
No. Green, white, and brown wire perform identically regardless of whether it is SPT-1 or SPT-2. Color is purely aesthetic. Match the wire color to the mounting surface. Green blends with trees and bushes. White blends with white fascia and eaves. Brown blends with wood surfaces.
Is SPT-2 wire required by code for outdoor Christmas lights?
The NEC does not specifically mandate SPT-2 for temporary holiday lighting. SPT-1 is perfectly acceptable for seasonal installations. SPT-2 is a better choice for permanent installations where the wire will be exposed to the elements year-round, but for seasonal work that goes up and comes down each year, SPT-1 meets all requirements.