How do SPT-1 and SPT-2 wires differ? We receive this inquiry regularly, and whenever we publish an article or create a video on this subject, it garners significant attention. Notably, this knowledge appeals not only to professional Christmas installers and enthusiasts but also to those who have no interest in holiday decorating. The question of SPT-1 versus SPT-2 extends beyond festive lighting, often puzzling people who frequently work with 16 gauge and 18 gauge electrical wires regarding the distinctions in SPT ratings.
Before delving deeper, I need to clarify that although I have over two decades of experience in the professional Christmas industry, I am not an electrician. The guidelines provided here are those we use for our installation teams and should be viewed as general advice, not expert electrical guidance. Always consult a licensed electrician familiar with the National Electrical Code for the most current information on electrical specifications and maximum amperage ratings.
Separating Facts from Myths
The debate over SPT-1 versus SPT-2 is more complex than it should be, and the question, “What's the Difference,” has sparked numerous discussions over the years. Unfortunately, much of the information circulating is inaccurate, adding to the confusion. A recent online search I conducted revealed that roughly 30% of the information is somewhat incorrect and another 40% is completely wrong.
Simply put, the difference between SPT-1 and SPT-2 lies in the insulation thickness. SPT-1 is .03”, whereas SPT-2 is .045”. This is the sole physical difference between the two ratings. Most resources agree on this point. The confusion arises when discussing maximum amperage ratings. Many specifications claim that SPT-1 has a max rating of 7 amps and SPT-2 of 10 amps, which is inaccurate. The actual maximum amperage load depends on the copper content and the length of the cord, not the insulation thickness. In summary, the only difference between the two SPT numbers is the insulation thickness, with SPT-2 having 50% thicker insulation than SPT-1. This does not alter the maximum power capacity of the wire.
The table below is what we reference when training our installation teams and advising other professional Christmas installers:
As highlighted in the table, the cord's length determines its maximum amperage capacity, independent of the SPT rating.
Which Is Superior, SPT-1, or SPT-2?
This brings us to the next query: which type of cord is superior? Unfortunately, the answer is complicated and has been a subject of debate in the professional Christmas industry for years. Some installers and enthusiasts favor SPT-1, while others prefer SPT-2, with reasons varying significantly but typically falling into one of these four categories.
- • Assuming SPT-2 has a higher maximum amperage load.
- • Believing SPT-1 is less durable in adverse weather.
- • Price differences between SPT-1 and SPT-2
- • Choosing SPT-1 for environmental reasons
Let's briefly examine these reasons to differentiate facts from misconceptions.
Incorrectly Believing SPT-2 Has a Higher Maximum Amperage Load
The top reason many opt for SPT-2 is the misconception that it has a higher maximum amperage load, which, as mentioned earlier, is not true. Both cords contain the same amount of copper and therefore share the same maximum amp rating. For 18 gauge cord (a standard in the Pro Christmas industry), the maximum usable amperage ranges from 5 to 10 amps depending on cord length: 10 amps for 0 to 50 feet, 7 amps for 51 to 150 feet, and 5 amps for over 150 feet. Longer runs, particularly those exceeding 200 feet, experience voltage drops, especially with C7 and C9 sockets. Additionally, never use more than 250 feet of 18 gauge wire, including an 18 gauge empty socket light line (C7 and C9 light line). For light lines, the maximum should not surpass 250 bulbs or 250 feet, whichever is less. Exceeding these limits leads to significant voltage drops and potential overheating, posing fire hazards.
Believing SPT-1 Is Less Durable in Adverse Weather
Generally, this is not true. We sell 18 gauge wire worldwide, used from tropical to frigid northern climates. SPT-1 performs well under most conditions for seasonal Christmas lighting and decoration setups. Note that Christmas string light sets have 22 gauge wire with relatively thin insulation, which also holds up well. Therefore, the considerably more robust 18 gauge, SPT-1, thrives even better in harsh environments.
There are scenarios where SPT-2 may be preferable. For installations extending beyond the standard 90-day holiday season, SPT-2's thicker insulation better withstands prolonged UV exposure, especially during summer months.
I must mention, to avoid a flood of negative feedback, that according to the National Electric Code, 18 gauge wire should only be used for seasonal lighting, defined as 90 days or less. Although this code is often disregarded, it's crucial to state explicitly that using an 18 gauge cord beyond 90 days does not comply with NEC standards.
SPT-2 is also recommended in extremely cold climates. While SPT-1 generally performs well, using SPT-2 in very cold regions such as Alaska, Canada, and other northern areas can be beneficial. Extreme cold and ice can push the limits of even the toughest electrical cords.
Price Differences Between SPT-1 and SPT-2
SPT-1 is more affordable than SPT-2, making it attractive, particularly for professional installers. Large Christmas installation companies can use hundreds of thousands of feet of C7 and C9 light lines annually, resulting in considerable savings by choosing SPT-1. For homeowners installing a few hundred feet of light line or creating a few extension cords with 18/2 electrical wire, the cost difference between SPT-1 and SPT-2 is negligible.
Environmental Considerations
Environmental concerns about SPT-1 or SPT-2 have only recently emerged. Since SPT-2 has 50% more insulation than SPT-1, it has a greater environmental impact. Increasingly, the public and large companies aim to reduce their environmental footprint where possible. Choosing a cord with significant insulation, leading to a higher carbon footprint, can motivate some to opt for SPT-1. While many professional Christmas installers and enthusiasts may not prioritize this concern, it can be influential in environmentally conscious regions like California, Colorado, and Oregon.
So, What's the Conclusion?
Which wire should be your preferred choice for stock electrical wire and C7 and C9 lighting? Ultimately, it's not an issue that should cause stress. Make a choice and proceed. If you are among the majority installing under normal seasonal conditions and prefer the most readily available cord, go with SPT-1. 75% of our sales are SPT-1, and it's what we use for our installations. However, if you favor thicker insulation, choose SPT-2. Regardless of your choice, ensure that the male and female connectors match the SPT rating of the cord to avoid complications during the installation season, especially for professional installers managing thousands of feet of cord and numerous plugs annually.
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